Tugas Struktur data

Pointer is a data type whose value refers to another value stored elsewhere in computer memory using its address. A data structure is an arrangement of data, either in the computer’s memory or on the diskstorage.Abstract Data Type (ADT) is a data type that is organized in such a way that the specification of the objects and the specification of the operations on the objects is separated from the representation of the objects and the implementation of the operations

The variables within a structure are of different data types and each has a name that is used to select it from the structure. Linked list is a data structure that consists of a sequence of data records such that each record there is a field that contains a reference to the next record in the sequence

Linked list is a data structure that consists of a sequence of data records such that each record there is a field that contains a reference to the next record in the sequence.Linked list which node contain only a single link to other node is called single linked list.Doubly linked list or two-way linked list is a linked list data structure with two link, one that contain reference to the next data and one that contain reference to the previous data.Double linkedlist is more simple than single linkedlist cause of it make easier when we use connected between 2 connector.

Tree is a collection of one or more nodes.Binary tree is a rooted tree data structure in which each node has at most two children.

There are 4 types of Binary Tree:PERFECT binary tree ,COMPLETE binary tree ,SKEWED binary tree ,BALANCED binary tree .

We can create an expression tree from a prefix or postfix by recursive.In prefix, you have to print/process before its child are processed.In postfix, you have to print/process after its child have been processed.






Assignment chapter 11

Student Assignment Chapter 11 Review (Mr. Tri Djoko Wahjono, Ir., M.Sc.) Discovering Computers Student Assignment – Chapter 11 Review Page 594-595

1. What are Computer Security Risks, and what are the types of Cybercrime Perpetrators? Computer security risk is any event or action that could cause a loss of or damage to computer hardware, software, data, information, or processing capability. While some breaches to computer security are accidental, many are intentional. Some intruders do no damage; they merely access data, information, or programs on the computer before logging off. Other intruders indicate some evidence of their presence either by leaving a message or by deliberately altering or damaging data. Any illegal act involving a computer generally is referred to as a computer crime. The term cybercrime refers to online or Internet-based illegal acts. Perpetrators of cybercrime and other intrusions fall into seven basic categories: hacker, cracker, script kiddies, corporate spy, unethical employee, cyber extortionist, and cyber terrorist.

2. What are various Internet and Networking Attacks, and how can Users Safeguard against these attacks? Various internet and networking attacks are: computer virus, worm, Trojan horse, and rootkit. A computer virus is a potentially damaging computer program that affects, or infects, a computer negatively by altering the way the computer works without the user’s knowledge or permission. A worm is a program that copies itself repeatedly, for example in memory or on a network, using up resources and possibly shutting down the computer or network. A Trojan horse (named after the Greek myth) is a program that hides within or looks like a legitimate program. A certain condition or action usually triggers the Trojan horse. Unlike a virus or worm, a Trojan horse does not replicate itself to other computers. A rootkit is a program that hides in a computer and allows someone from a remote location to take full control of the computer. Once the rootkit is installed, the rootkit author can execute programs, change settings, monitor activity, and access files on the remote computer. To take precautions against those malware, do not start a computer with removable media in the drives or ports. Never open an e-mail attachment unless you are expecting the attachment and it is from a trusted source. Disable macros in documents that are not from a trusted source. Install an antivirus program and a personal firewall. Stay informed about any new virus alert or virus hoax. To defend against a botnet, a denial of service attack, improper use of a back door, and spoofing, users can install a firewall, install intrusion detection software, and set up a honeypot.

3. What are techniques to prevent Unauthorized Computer Access and Use? Unauthorized access is the use of a computer or network without permission. Unauthorized use is the use of a computer or its data for unapproved or illegal activities. Organizations can take measures such as implementing a written acceptable use policy (AUP), a firewall, intrusion detection software, an access control, and an audit trail. Access controls include a user name and password or passphrase, a CAPTCHA, a possessed object, and a biometric device. Organizations take several measures to help prevent unauthorized access and use. At a mini mum, they should have a written acceptable use policy (AUP) that outlines the computer activities for which the computer and network may and may not be used. An organization’s AUP should specify the acceptable use of computers by employees for personal reasons. Some organizations prohibit such use entirely. Others allow personal use on the employee’s own time such as a lunch hour. To protect your personal computer from unauthorized intrusions, you should disable file and printer sharing on your Internet connection. Other measures that safeguard against unauthorized access and use include firewalls and intrusion detection software, which were discussed in the previous section, and identifying and authenticating users.

4. What are safeguard against Hardware Theft and Vandalism? Hardware theft and vandalism are other types of computer security risks. Hardware theft is the act of stealing computer equipment. Hardware vandalism is the act of defacing or destroying computer equipment. To help reduce the chances of theft, companies and schools use a variety of security measures. Physical access controls, such as locked doors and windows, usually are adequate to protect the equipment. Many businesses, schools, and some homeowners install alarm systems for additional security. School computer labs and other areas with a large number of semi frequent users often attach additional physical security devices such as cables that lock the equipment to a desk, cabinet, or floor. Small locking devices also exist that require a key to access a hard disk or optical disc drive. Some businesses use a real time location system (RTLS) to track and identify the location of high-risk or high-value items.

5. How do software manufacturers protect against software piracy? To protect themselves from software piracy, software manufacturers issue users license agreements. A license agreement is the right to use the software. That is, you do not own the software. The license agreement provides specific conditions for use of the software, which a user must accept before using the software. These terms usually are displayed when you install the software. In an attempt to prevent software piracy, Microsoft and other manufacturers have incorporated an activation process into many of their consumer products. During the product activation, which is conducted either online or by telephone, users provide the software product’s 25-character identification number to receive an installation identification number unique to the computer on which the software is installed. Usually, the software does not function or has limited functionality until you activate it via the Internet or telephone.

6. How does encryption work, and why it is necessary? Encryption is a process of converting readable data into unreadable characters to prevent unauthorized access. You treat encrypted data just like any other data. That is, you can store it or send it in an e-mail message. In the encryption process, the unencrypted, readable data is called plaintext. The encrypted (scrambled) data is called ciphertext. An encryption algorithm, or cypher, is a set of steps that can convert readable plaintext into unreadable ciphertext. Encryption programs typically use more than one encryption algorithm, along with an encryption key. Encryption is used to protect information on the Internet and networks.

7. What types of devices are available to protect computers from system failure? A system failure is the prolonged malfunction of a computer. System failure also can cause loss of hardware, software, data, or information. A variety of causes can lead to system failure. A common cause of system failure is an electrical power variation such as noise, an undervoltage, or an overvoltage. To protect against electrical power variations, use a surge protector. A surge protector, also called a surge suppressor, uses special electrical components to smooth out minor noise, provide a stable current flow, and keep an overvoltage from reaching the computer and other electronic equipment. For additional electrical protection, some users connect an uninterruptible power supply to the computer. An uninterruptible power supply (UPS) is a device that contains surge protection circuits and one or more batteries that can provide power during a temporary or permanent loss of power. A UPS connects between your computer and a power source.

8. What are options for backing up computer resources? To protect against data loss caused by system failure or hardware/software/information theft, computer users should back up files regularly. A backup is a duplicate of a file, program, or disk that can be used if the original is lost, damaged, or destroyed. Thus, to back up a file means to make a copy of it. In the case of system failure or the discovery of corrupted files, you restore the files by copying the backed up files to their original location on the computer. You can use just about any media to store backups. Be sure to use high-quality media. A good choice for a home user might be optical discs or external hard disks. Home and business users keep backup copies offsite so that a single disaster, such as a fire, does not destroy both the original and the backup copy of the data. An offsite location can be a safe deposit box at a bank or a briefcase. A growing trend is to use cloud storage as an offsite location. Most backup programs for the home user provide for a full backup and a selective backup. Some users implement a three-generation backup policy to preserve three copies of important files.

9.What risks and safeguards are associated with wireless communications? Although wireless access provides many conveniences to users, it also poses additional security risks. One study showed that about 80 percent of wireless networks have no security protection. Some perpetrators connect to other’s wireless networks to gain free Internet access; others may try to access an organization’s confidential data. In one technique, called war driving or access point mapping, individuals attempt to detect wireless networks via their notebook computer or mobile device while driving a vehicle through areas they suspect have a wireless network. Some individuals instead use war flying, where they use airplanes instead of vehicles to detect unsecured wireless networks. Once located, some individuals use a GPS device to add the WAP to a war driving access point map on the Internet, making the wireless network vulnerable. In addition to using firewalls, some safeguards that improve the security of wireless networks include reconfiguring the wireless access point and ensuring equipment uses one or more wireless security standards such as Wi-Fi Protected Access and 802.11i. • A wireless access point (WAP) should be configured so that it does not broadcast a network name, known as an SSID (service set identifier). Users should change the default SSID to prevent unauthorized users from accessing their wireless network. The WAP also can be programmed so that only certain devices can access it. • Wi-Fi Protected Access (WPA) is a security standard that improves on older security standards by authenticating network users and providing more advanced encryption techniques. • An 802.11i network, sometimes called WPA2, the most recent network security standard, conforms to the government’s security standards and uses more sophisticated encryption techniques than WPA.

10. How can health-related disorders and injuries due to computer use be prevented? A repetitive strain injury (RSI) is an injury or disorder of the muscles, nerves, tendons, ligaments, and joints. Computer-related RSIs include tendonitis and carpal tunnel syndrome. For prevented this, OSHA (Occupational Safety and Health Administration) has developed industry-specific and task-specific guidelines designed to prevent workplace injuries with respect to computer usage. Tendonitis is inflammation of a tendon due to repeated motion or stress on that tendon. Carpal tunnel syndrome (CTS) is inflammation of the nerve that connects the forearm to the palm of the wrist. Repeated or forceful bending of the wrist can cause CTS or tendonitis of the wrist. Symptoms of tendonitis of the wrist include extreme pain that extends from the forearm to the hand, along with tingling in the fingers. Symptoms of CTS include burning pain when the nerve is compressed, along with numbness and tingling in the thumb and first two fingers. You can take many precautions to prevent these types of injuries. Take frequent breaks during the computer session to exercise your hands and arms. To prevent injury due to typing, place a wrist rest between the keyboard and the edge of your desk. To prevent injury while using a mouse, place the mouse at least six inches from the edge of the desk. In this position, your wrist is flat on the desk. Finally, minimize the number of times you switch between the mouse and the keyboard, and avoid using the heel of your hand as a pivot point while typing or using the mouse. Another type of health-related condition due to computer usage is computer vision syndrome (CVS). You may have CVS if you have sore, tired, burning, itching, or dry eyes; blurred or double vision; distance blurred vision after prolonged staring at a display device; headache or sore neck; difficulty shifting focus between a display device and documents; difficulty focusing on the screen image; color fringes or after-images when you look away from the display device; and increased sensitivity to light. To ease eyestrain, take these techniques: • Every 10 to 15 minutes, take an eye break. – Look into the distance and focus on an object for 20 to 30 seconds. – Roll your eyes in a complete circle. – Close your eyes and rest them for at least one minute. • Blink your eyes every five seconds. • Place your display device about an arm’s length away from your eyes with the top of the screen at eye level or below. • Use large fonts. • If you wear glasses, ask your doctor about computer glasses. • Adjust the lighting.

11.What are issues related to information accuracy, intellectual property rights, codes of conduct, and green computing? Computer ethics are the moral guidelines that govern the use of computers and information systems. Seven frequently discussed areas of computer ethics are unauthorized use of computers and networks, software theft (piracy), information accuracy, intellectual property rights, codes of conduct, information privacy, and green computing. Information accuracy today is a concern because many users access information maintained by other people or companies, such as on the Internet. Be aware that the organization providing access to the information may not be the creator of the information. In addition to concerns about the accuracy of computer input, some individuals and organizations raise questions about the ethics of using computers to alter output, primarily graphical output such as a retouched photo. Using graphics equipment and software, users easily can digitize photos and then add, change, or remove images. Intellectual property rights are the rights to which creators are entitled for their work. A copyright gives authors and artists exclusive rights to duplicate, publish, and sell their materials. A copyright protects any tangible form of expression. A common infringement of copyright is piracy. People pirate (illegally copy) software, movies, and music. Many areas are not clear cut with respect to the law, because copyright law gives the public fair use to copyrighted material. The issues surround the phrase, fair use, which allows use for educational and critical purposes. IT code of conduct is a written guideline that helps determine whether a specific computer action is ethical or unethical. Green computing involves reducing the electricity and environmental waste while using a computer. People use, and often waste, resources such as electricity and paper while using a computer.

12.What are issues surrounding information privacy? Information privacy is the right of individuals and companies to deny or restrict the collection and use of information about them. Issues surrounding information privacy include the following. An electronic profile combines data about an individual’s Web use with data from public sources, which then is sold. A cookie is a file that a Web server stores on a computer to collect data about the user. Spyware is a program placed on a computer that secretly collects information about the user. Adware is a program that displays an online advertisement in a banner or pop-up window. Spam is an unsolicited e-mail message or newsgroup posting sent to many recipients or newsgroups at once. Phishing is a scam in which a perpetrator attempts to obtain personal or financial information. The concern about privacy has led to the enactment of many federal and state laws regarding the disclosure of data. As related to the use of computers, social engineering is defined as gaining unauthorized access or obtaining confidential information by taking advantage of the trusting human nature of some victims and the naivety of others. Employee monitoring uses computers to observe, record, and review an employee’s computer use. Content filtering restricts access to certain materials on the Web.

assignment chapter 10

lecturer : Mr. Tri Djoko Wahjono, Ir.M.Sc

  1. What is a Database, and How does a Database interact with data and information?

A database is an organized collection of data. The data are typically organized to model relevant aspects of reality in a way that supports processes requiring this information. For example, modeling the availability of rooms in hotels in a way that supports finding a hotel with vacancies.

Database management systems (DBMSs) are specially designed applications that interact with the user, other applications, and the database itself to capture and analyze data. A general-purpose database management system (DBMS) is a software system designed to allow the definition, creation, querying, update, and administration of databases. Well-known DBMSs include MySQL, PostgreSQL, SQLite, Microsoft SQL Server, Oracle, SAP, dBASE, FoxPro, IBM DB2, LibreOffice Base and FileMaker Pro. A database is not generally portable across different DBMS, but different DBMSs can interoperate by using standards such as SQL and ODBC or JDBC to allow a single application to work with more than one database.


Formally, the term “database” refers to the data itself and supporting data structures. Databases are created to operate large quantities of information by inputting, storing, retrieving, and managing that information. Databases are set up so that one set of software programs provides all users with access to all the data.

A “database management system” (DBMS) is a suite of computer software providing the interface between users and a database or databases. Because they are so closely related, the term “database” when used casually often refers to both a DBMS and the data it manipulates.

Outside the world of professional information technology, the term database is sometimes used casually to refer to any collection of data (perhaps a spreadsheet, maybe even a card index). This article is concerned only with databases where the size and usage requirements necessitate use of a database management system.

The interactions catered for by most existing DBMS fall into four main groups:

  • Data definition. Defining new data structures for a database, removing data structures from the database, modifying the structure of existing data.
  • Update. Inserting, modifying, and deleting data.
  • Retrieval. Obtaining information either for end-user queries and reports or for processing by applications.
  • Administration. Registering and monitoring users, enforcing data security, monitoring performance, maintaining data integrity, dealing with concurrency control, and recovering information if the system fails.

A DBMS is responsible for maintaining the integrity and security of stored data, and for recovering information if the system fails.

Both a database and its DBMS conform to the principles of a particular database model. “Database system” refers collectively to the database model, database management system, and database.

Physically, database servers are dedicated computers that hold the actual databases and run only the DBMS and related software. Database servers are usually multiprocessor computers, with generous memory and RAID disk arrays used for stable storage. RAID is used for recovery of data if any of the disks fails. Hardware database accelerators, connected to one or more servers via a high-speed channel, are also used in large volume transaction processing environments. DBMSs are found at the heart of most database applications. DBMSs may be built around a custom multitasking kernel with built-in networking support, but modern DBMSs typically rely on a standard operating system to provide these functions. Since DBMSs comprise a significant economical market, computer and storage vendors often take into account DBMS requirements in their own development plans.

Databases and DBMSs can be categorized according to the database model(s) that they support (such as relational or XML), the type(s) of computer they run on (from a server cluster to a mobile phone), the query language(s) used to access the database (such as SQL or XQuery), and their internal engineering, which affects performance, scalability, resilience, and security.

2.What is Data Integrity, and what are the qualities of valuable information?

Data integrity refers to maintaining and assuring the accuracy and consistency of data over its entire life-cycle, and is a critical aspect to the design, implementation and usage of any system which stores, processes or retrieves data. The term data integrity is broad in scope and may have widely different meanings depending on the specific context – even under the same general umbrella of computing. This article provides only a broad overview of some of the different types and concerns of data integrity.

Data integrity is the opposite of data corruption, which is a form of data loss. The overall intent of any data integrity technique is the same: ensure data is recorded exactly as intended (such as a database correctly rejecting mutually exclusive possibilities,) and upon later retrieval, ensure the data is the same as it was when it was originally recorded. In short, data integrity aims to prevent unintentional changes to information. Data integrity is not to be confused with data security, the discipline of protecting data from unauthorized parties.

Any unintended changes to data as the result of a storage, retrieval or processing operation, including malicious intent, unexpected hardware failure, and human error, is failure of data integrity. If the changes are the result of unauthorized access, it may also be a failure of data security. Depending on the data involved this could manifest itself as benign as a single pixel in an image appearing a different color than was originally recorded, to the loss of vacation pictures or a business-critical database, to even catastrophic loss of human life in a Life-critical system.

3.What is meant by Character, Field, Record, and File?

Data is classified in a hierarchy, with each level of data consisting of one or more items from the lower level. A bit is the smallest unit of data a computer can process. Eight bits grouped together in an unit form a byte, and each byte represents a single character, which can be a number, letter, space, punctuation mark, or other symbol.

A Field is a combination of one or more related characters or bytes and is the smallest unit of data a user accesses.

A Record is a group of related fields.

A Data File is a collection of related records stored on a storage medium such as a hard disk or optical disc.

4.What are file maintenance techniques and validation techniques?

File maintenance refers to the procedures that keep data current. File maintenance procedures include adding records to correct inaccurate data or to update old data with new data, and deleting records when they no longer are needed.

Validation is the process of comparing data with a set of rules or values to find out if the data is correct. Many programs perform a validity check that analyzes data, either as you enter it or after you enter it, to help ensure that it is correct.

Types of validity checks include an alphabetic check, a numeric check, a range check, a consistency check, a completeness check, and a check digit.

5.How is a file processing approach different from database approach?

Each department or area within an organization has its own set of data files. The records in one file may not relate to the records in any other file. Two major weaknesses of file processing systems are redundant data (duplicated data) and isolated data. With a database approach, many programs and users share the data in database. The database approach reduces data redundancy, improves data integrity, shares data, permits easier access, and reduces development time. A database, however, can be more complex than a file processing system, requiring special training and more computer memory, storage, and processing power than file processing systems. Data in a database also can be more vulnerable than data in file processing systems.

6.What functions are common to most database management systems?

Database management system – (DBMS) A suite of programs which typically manage large structured sets of persistent data, offering ad hoc query facilities to many users. They are widely used in business applications.

A database management system (DBMS) can be an extremely complex set of software programs that controls the organization, storage and retrieval of data (fields, records and files) in a database. It also controls the security and integrity of the database. The DBMS accepts requests for data from the application program and instructs the operating system to transfer the appropriate data.

When a DBMS is used, information systems can be changed much more easily as the organization’s information requirements change. New categories of data can be added to the database without disruption to the existing system.

Data security prevents unauthorized users from viewing or updating the database. Using passwords, users are allowed access to the entire database or subsets of the database, called subschemas (pronounced “sub-skeema”). For example, an employee database can contain all the data about an individual employee, but one group of users may be authorized to view only payroll data, while others are allowed access to only work history and medical data.

The DBMS can maintain the integrity of the database by not allowing more than one user to update the same record at the same time. The DBMS can keep duplicate records out of the database; for example, no two customers with the same customer numbers (key fields) can be entered into the database.

Query languages and report writers allow users to interactively interrogate the database and analyze its data.

If the DBMS provides a way to interactively enter and update the database, as well as interrogate it, this capability allows for managing personal databases. However, it may not leave an audit trail of actions or provide the kinds of controls necessary in a multi-user organization. These controls are only available when a set of application programs are customized for each data entry and updating function.

A business information system is made up of subjects (customers, employees, vendors, etc.) and activities (orders, payments, purchases, etc.). Database design is the process of deciding how to organize this data into record types and how the record types will relate to each other. The DBMS should mirror the organization’s data structure and process transactions efficiently.

Organizations may use one kind of DBMS for daily transaction processing and then move the detail onto another computer that uses another DBMS better suited for random inquiries and analysis. Overall systems design decisions are performed by data administrators and systems analysts. Detailed database design is performed by database administrators.

The three most common organizations are the hierarchical database, network database and relational database. A database management system may provide one, two or all three methods. Inverted lists and other methods are also used. The most suitable structure depends on the application and on the transaction rate and the number of inquiries that will be made.

Database machines are specially designed computers that hold the actual databases and run only the DBMS and related software. Connected to one or more mainframes via a high-speed channel, database machines are used in large volume transaction processing environments. Database machines have a large number of DBMS functions built into the hardware and also provide special techniques for accessing the disks containing the databases, such as using multiple processors concurrently for high-speed searches.

The world of information is made up of data, text, pictures and voice. Many DBMSs manage text as well as data, but very few manage both with equal proficiency. Throughout the 1990s, as storage capacities continue to increase, DBMSs will begin to integrate all forms of information. Eventually, it will be common for a database to handle data, text, graphics, voice and video with the same ease as today’s systems handle data.

7.What are Characteristics of relational, object-oriented, and multidimensional databases?

This isn’t the first time in recent history that new types of database products have emerged and overcome RDBMS inefficiencies. Back in the 1980s, a class of applications was identified in which RDBMS products ill-handled the data-management needs (especially the generation of RDBMSs available at that time).

These applications all needed user-specified data types that varied among different implementations. For example, computer-aided design/computer-aided manufacturing (CAD/CAM) applications had to be capable of specifying data types that related to product drawings, blueprints, and other related factors.

Computer-aided software engineering (CASE) needed data types to represent applications and systems, databases, graphical representations of entities and attributes, process and data flows, and other parts of the application-development process.

What resulted was object-oriented database management systems (ODBMSs), which eliminated the table-row-column structures of relational databases and instead introduced the concepts of classes and subclasses (or types and subtypes), objects, properties, methods, and the other parts of object-oriented technology directly into the database engine.

Because RDBMS technology wasn’t well-suited to multidimensional analysis, particularly in terms of performance, vendors set out to develop their own structures tuned and optimized for improved performance.

If you track happenings in the database management world, you’re probably familiar with the convergence of relational and object-oriented database technology. RDBMS products are being equipped with object-oriented extensions.

Arguably, this approach to handling complex data types (objects) has won out over non-relational products (“pure” ODBMSs), primarily because of the large installed base of relational products and applications running on top of them. Will the same thing happen in the data warehousing world — relational technology overtaking and then overwhelming specialized multidimensional products? Only time will tell.

8.How are Web Databases Accessed?

You can use Access 2010 and Access Services, a new component of SharePoint, to build web database applications. This helps you:

  • Secure and manage access to your data
  • Share data throughout an organization, or over the Internet
    Note    A user account is required to use a web database. Anonymous access is not supported.
  • Create database applications that don’t require Access to use

9.What are the responsibilities of Database Analysts and Administrators?

A database administrator’s responsibilities can include the following tasks:

  • Installing and upgrading the database server and application tools
  • Allocating system storage and planning future storage requirements for the database system
  • Modifying the database structure, as necessary, from information given by application developers verbally
  • Enrolling users and maintaining system security
  • Ensuring compliance with database vendor license agreement
  • Controlling and monitoring user access to the database
  • Monitoring and optimizing the performance of the database
  • Planning for backup and recovery of database information
  • Maintaining archived data
  • Backing up and restoring databases
  • Contacting database vendor for technical support
  • Generating various reports by querying from database as per need.


assignment chapter 9

lecturer : Mr. Tri Djoko Wahjono, Ir.M.Sc


  1. What Is the Purpose of the Components Required for Successful Communications, and What Are Various Sending and Receiving Devices?

Computer communications describes a process in which two or more computers or devices transfer data, instructions, and information. Today, even the smallest computers and devices can communicate directly with one another, with hundreds of computers on a company network, or with millions of other computers.

For successful communications, you need the following:

  • • A sending device that initiates an instruction to transmit data, instructions, or information.
  • • A communications device that connects the sending device to a communications channel.
  • • A communications channel, or transmission media on which the data, instructions, or information travel.
  • • A communications device that connects the communications channel to a receiving device.
  • • A receiving device that accepts the transmission of data, instructions, or information.

Some devices that serve as sending devices and receiving devices are

(a) mainframe computers,

(b) servers,

(c) desktop computers,

(d) notebook computers,

(e) smart phones,

(f) Internet-enabled portable media players,

(g) handheld game consoles, and

(h) GPS receivers.

The communications channel consists of telephone and power lines, cable television and other underground lines, microwave stations, and satellites.

2.How Are Computer Communications Used?

Computer communications are everywhere. Many require that users subscribe to an Internet access provider. With other computer communications, an organization such as a business or school provides communications services to employees, students, or customers.

The following pages discuss a variety of computer communications. Communications technologies include blogs, chat rooms, e-mail, fax, FTP, instant messaging, newsgroups, RSS, video conferencing, VoIP, Web, Web folders, and wikis. Users can send and receive wireless messages to and from smart phones, cell phones, handheld game consoles, and other mobile devices using text messaging, picture messaging and video messaging, and wireless instant messaging. People connect wirelessly to the Internet through a wireless Internet access point. A hot spot is a wireless network that provides Internet connections to mobile computers and devices. A cybercafé is a coffeehouse, restaurant, or other location that provides computers with Internet access. A global positioning system (GPS) analyzes signals sent by satellites to determine an earth-based receiver’s geographic location. Many software products provide a means to collaborate, or work online with other users connected to a server. Groupware is software that helps groups of people work on projects or share information over a network.

Voice mail allows someone to leave a voice message for one or more people. Web services describe standardized software that enables programmers to create applications that communicate with other remote computers.

3.What Are the Advantages of Using a Network, and How Are LANs, MANs, and WANs Different?

a network is a collection of computers and devices  connected together via communications devices and transmission media. Many businesses network their computers together to facilitate communications, share hardware, share data and information, share software, and transfer funds.

  • • Facilitating communications — Using a network, people communicate efficiently and easily via e-mail, instant messaging, chat rooms, blogs, wikis, online social networks, video telephone calls, online meetings, video conferencing, VoIP, wireless messaging services, and groupware.
  • • Sharing hardware — In a networked environment, each computer on the network can have access to hardware on the network. Business and home users network their hardware to save money.
  • • Sharing data and information — In a networked environment, any authorized computer user can access data and information stored on other computers on the network.
  • • Sharing software — Users connected to a network have access to software on the network.

To support multiple users’ access of software, most vendors sell network versions or site licenses of their software, which usually cost less than buying individual copies of the software for each computer.

  • • Transferring funds — Called electronic funds transfer (EFT ), it allows users connected to a network to transfer money from one bank account to another via transmission media.

LANs, MANs, and WANs

Networks usually are classified as a local area network, metropolitan area network, or wide area network. The main differentiation among these classifications is their area of coverage.

  • LAN (local area network) is a network that connects computers and devices in a limited geographical area such as a home, school computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network, called a node, often shares resources such as printers, large hard disks, and programs.Often, the nodes are connected via cables.
  • MAN (metropolitan area network) is a high-speed network that connects local area networks in a metropolitan area such as a city or town and handles the bulk of communications activity across that region. A MAN typically includes one or more LANs, but covers a smaller geographic area than a WAN. A MAN usually is managed by a consortium of users or by a single network provider that sells the service to the users. Local and state governments, for example, regulate some MANs. Telephone companies, cable television operators, and other organizations provide users with connections to the MAN.
  • WAN (wide area network) is a network that covers a large geographic area (such as a city, country, or the world) using a communications channel that combines many types of media such as telephone lines, cables, and radio waves (Figure 9-12). A WAN can be one large network or can consist of two or more LANs connected together. The Internet is the world’s largest WAN.

4.How Are a Client/Server and Peer-to-Peer Network Different, and How Does a P2P Network Work?

  • Client/Server

On a client/server network, one or more computers act as a server, and the other computers on the network request services from the server. A server, sometimes called a host computer, controls access to the hardware, software, and other resources on the network and provides a centralized storage area for programs, data, and information. The clients are other computers and mobile devices on the network that rely on the server for its resources. For example, a server might store a database of customers. Clients on the network (company employees) access the customer database on the server.

  • Peer-to-Peer

One type of peer-to-peer network is a simple, inexpensive network that typically connects fewer than 10 computers. Each computer, called a peer, has equal responsibilities and capabilities, sharing hardware (such as a printer), data, or information with other computers on the peer-to-peer network. Each computer stores files on its own storage devices. Thus, each computer on the network contains both the server operating system and application software. All computers on the network share any peripheral device(s).attached to any computer. For example, one computer may have a laser printer and a scanner, while another has an ink-jet printer and an external hard disk. Peer-to-peer networks are ideal for very small businesses and home users.

  • Another type of peer-to-peer, called P2P, describes an Internet network on which users access each other’s hard disks and exchange files directly over the Internet. This type of peer-to peer network sometimes is called a file sharing network because users with compatible software and an Internet connection copy files from someone else’s hard disk to their hard disks. As more users connect to the network, each user has access to shared files on other users’ hard disks. When users log off the network, others no longer have access to their hard disks.

5.How Are a Star Network, Bus Network, and Ring Network Different?

  • Star Network

On a star network, all of the computers and devices (nodes) on the network connect to a central device, thus forming a star. Two types of devices that provide a common central connection point for nodes on the network are a hub and a switch. All data that transfers from one node to another passes through the hub or switch. Star networks are fairly easy to install and maintain. Nodes can be added to and removed from the network with little or no disruption to the network. On a star network, if one node fails, only that node is affected. The other nodes continue to operate normally. If the hub or switch fails, however, the entire network is inoperable until the device is repaired. Most large star networks, therefore, keep backup hubs or switches available in case the primary one fails.

  • Bus Network

A bus network consists of a single central cable, to which all computers and other devices connect. The bus is the physical cable that connects the computers and other devices. The bus in a bus network transmits data, instructions, and information in both directions. When a sending device transmits data, the address of the receiving device is included with the transmission so that the data is routed to the appropriate receiving device. Bus networks are popular on LANs because they are inexpensive and easy to install. One advantage of the bus network is that computers and other devices can be attached and detached at any point on the bus without disturbing the rest of the network.

  • Ring Network

On a ring network, a cable forms a closed loop (ring) with all computers and devices arranged along the ring. Data transmitted on a ring network travels from device to device around the entire ring, in one direction. When a computer or device sends data, the data travels to each computer on the ring until it reaches its destination. If a computer or device on a ring network fails, the entire network potentially could stop functioning. A ring network can span a larger distance than a bus network, but it is more difficult to install. The ring topology primarily is used for LANs, but also is used in WANs.

6.What Are Various Network Communications Standards?

A network standard defines guidelines that specify the way computers access a medium, the type(s) of medium, the speeds on different types of networks, and the type of physical cable or wireless technology used. Network communications standards include the following. Ethernet specifies that no central computer or device on the network should control when data can be transmitted. Token ring requires devices to share or pass a special signal, called a token. TCP/IP divides data into packets. Wi-Fi identifies any network based on the 802.11 standards for wireless communications.  Bluetooth uses short-range radio waves to transmit data. UWB specifies how two UWB devices use short-range radio waves to communicate at high speeds. IrDA transmits data wirelessly via infrared light waves. RFID uses radio signals for communications. WiMAX is a network standard developed by IEEE that specifies how wireless devices communicate over the air in a wide area. The Wireless Application Protocol (WAP) specifies how some mobile devices can display Internet content.

7.What Is the Purpose of Communications Software?

Communications software consists of programs that (1) help users establish a connection to another computer or network; (2) manage the transmission of data, instructions, and information; and (3) provide an interface for users to communicate with one another. The first two are system software and the third is application software. Chapter 3 presented a variety of examples of application software for communications: e-mail, FTP, Web browser, newsgroup/message boards, chat rooms, instant messaging, video conferencing, and VoIP. Sometimes, communications devices are preprogrammed to accomplish communications tasks. Other communications devices require separate communications software to ensure proper transmission of data. Communications software works with the network standards and protocols just discussed to ensure data moves through the network or the Internet correctly. Communications software usually is bundled with the operating system or purchased network devices. Communications software helps users establish a connection to another computer or network; manages the transmission of data, instructions, and information; and  provides an interface for users to communicate with one another.


8.What Are Various Types of Lines for Communications over the Telephone Network?

  • Dial-Up Lines

A dial-up line is a temporary connection that uses one or more analog telephone lines for communications. A dial-up connection is not permanent. a dial-up line to connect computers costs no more than making a regular telephone call.

  • Dedicated Lines

Satellite local access area local telephone company A dedicated line is a type of always on connection that is established between two communications devices (unlike a dial-up line where the connection is reestablished each time it is used). The quality and consistency of the  connection on a dedicated line are better than a dial-up line because dedicated lines provide a constant connection. Businesses often use dedicated lines to connect geographically distant offices. Dedicated lines can be either analog or digital. Digital lines increasingly are connecting home and business users to networks around the globe because they transmit data and information at faster rates than analog lines. Five types of digital dedicated lines are ISDN lines, DSL, FTTP, T-carrier lines, and ATM.

  • ISDN Lines

For the small business and home user, an ISDN line provides faster transfer rates than dial-up telephone lines. Not as widely used today as in the past, ISDN (Integrated Services Digital Network) is a set of standards for digital transmission of data over standard copper telephone lines. With ISDN, the same telephone line that could carry only one computer signal now can carry three or more signals at once through the same line, using a technique called multiplexing.

  • DSL

DSL is a popular digital line alternative for the small business or home user. DSL (Digital Subscriber Line) transmits at fast speeds on existing standard copper telephone wiring.

Some DSL installations include a dial tone, providing users with both voice and data communications. These DSL installations often require that filters be installed to reduce noise interference when voice communications share the same line. ADSL is one of the more popular types of DSLs. As shown in Figure 9-25, ADSL (asymmetric digital subscriber line) is a type of DSL that supports faster transfer rates when receiving data (the downstream rate) than when sending data (the upstream rate). ADSL is ideal for Internet access because most users download more information from the Internet than they upload.

  • FTTP

FTTP, which stands for Fiber to the Premises, uses fiber-optic cable to provide extremely high-speed Internet access to a user’s physical permanent location. Two specific types of FTTP are FTTH and FTTB. FTTH (Fiber to the Home) provides home users with Internet access via fiber-optic cable. Similarly, FTTB (Fiber to the Building) refers to small businesses that use fiber-optic cables to access the Internet. With FTTP service, an optical terminal at your location receives the signals and transfers them to a router connected to your computer. As the cost of installing fiber decreases, more homes and businesses will opt for this high-speed Internet access.

  • T-Carrier Lines

A T-carrier line is any of several types of long-distance digital telephone lines that carry multiple signals over a single communications line. Where as a standard dial-up telephone line carries only one signal, digital T-carrier lines use multiplexing so that multiple signals share the line. T-carrier lines provide very fast data transfer rates. Only medium to large companies usually can afford the investment in T-carrier lines because these lines are so expensive.

  • ATM

ATM (Asynchronous Transfer Mode) is a service that carries voice, data, video, and multimedia at very high speeds. Telephone networks, the Internet, and other networks with large amounts of traffic use ATM. Some experts predict that ATM eventually will become the Internet standard for data transmission, replacing T3 lines.

9.What Are Commonly Used Communications Devices?

A communications device is hardware capable of transmitting data between a sending device and a receiving device. A dial-up modem converts digital signals to analog signals and analog signals to digital signals. So that data can travel along analog telephone lines. A digital modem sends and receives data and information to and from a digital line. An ISDN modem transmits digital data to and from an ISDN line, while a DSL modem transmits digital data to and from a DSL line. A cable modem, sometimes called a broadband modem, is a digital modem that sends and receives digital data over the cable television network. A wireless modem uses the cell phone network to connect to the Internet wirelessly from mobile computers and devices. A network card enables a computer or device that does not have built-in networking capability to access a network. A wireless access point allows computers and devices to transfer data wirelessly. A router connects multiple computers or other routers together and transmits data to its correct destination on the network. A hub or switch is a device that provides a central point for cables in a network.

10.How Can a Home Network Be Set Up?

A home network connects multiple computers and devices in a home. An Ethernet network connects each computer to a hub with a physical cable. A home power line cable network uses the same lines that bring electricity into the house. A phone line network uses existing telephone lines in a home. Most home networks use a Wi-Fi network.


11.What Are Various Physical and Wireless Transmission Media?


  • Twisted-Pair Cable

One of the more widely used transmission media for network cabling and telephone systems is twisted-pair cable. Twisted-pair cable consists of one or more twisted-pair wires bundled together. Each twisted-pair wire consists of two separate insulated copper wires that are twisted together. The wires are twisted together to reduce noise. Noise is an electrical disturbance that can degrade communications.

  • Coaxial Cable

Coaxial cable, often referred to as coax (pronounced KO-ax), consists of a single  copper wire surrounded by at least three layers: (1) an insulating material, (2) a woven or braided metal, and (3) a plastic outer coating (Figure 9-37). Cable television (CATV) network wiring often uses coaxial cable because it can be cabled over longer distances than twisted-pair cable. Most of today’s computer networks, however, do not use coaxial cable because other transmission media such as fiber-optic cable transmit signals at faster rates.

  • Fiber-Optic Cable

The core of a fiber-optic cable consists of dozens or hundreds of thin strands of glass or plastic that use light to transmit signals. Each strand, called an optical fiber, is as thin as a human hair. Inside the fiber-optic cable, an insulating glass cladding and a protective coating surround each optical fiber. Fiber-optic cables have the following advantages over cables that use wire, such as twisted-pair and coaxial cables:

  • • Capability of carrying significantly more signals than wire cables
  • • Faster data transmission
  • • Less susceptible to noise (interference) from other devices such as a copy machine
  • • Better security for signals during transmission because they are less susceptible to noise
  • • Smaller size (much thinner and lighter weight)
  • Broadcast radio distributes radio signals through the air over long and short distances.
  • Cellular radio is a form of broadcast radio that is used widely for mobile communications.
  • Microwaves are radio waves that provide a high speed signal transmission.
  • A communications satellite is a space station that receives microwave signals from an earth-based station, amplifies the signals, and broadcasts the signals back over a wide area.



assignment chapter 8

lecturer : Mr. Tri Djoko Wahjono, Ir.M.Sc

  1. What is system software, and what are the two types of system software?

System software (or systems software) is computer software designed to operate and control the computer hardware and to provide a platform for running application software.

The two types of system software :

  1. The operating system (prominent examples being z/OS, Microsoft Windows, Mac OS X and Linux), allows the parts of a computer to work together by performing tasks like transferring data between memory and disks or rendering output onto a display device. It also provides a platform to run high-level system software and application software
  2. Utility software helps to analyze, configure, optimize and maintain the computer

2.What are the functions of an operating system?

    1. Booting the computer
    2. Performs basic computer tasks eg managing the various peripheral devices eg mouse, keyboard
    3. Provides a user interface, e.g. command line, graphical user interface (GUI)
    4. Handles system resources such as computer’s memory and sharing of the central processing unit (CPU) time by various applications or peripheral devices
    5. Provides file management which refers to the way that the operating system manipulates, stores, retrieves and saves data
  1. What is the startup process on a personal computer?

In computing, booting (also known as booting up) is the initial set of operations that a computer system performs after electrical power to the CPU is switched on or when the computer is reset. The process begins when a computer is turned on for the first time, is re-energized after being turned off, when it is reset or when the operator invokes a LOAD function from the console, and ends when the computer is ready to perform its normal operations. On modern general purpose computers, this can take tens of seconds and typically involves performing a power-on self-test, locating and initializing peripheral devices, and then finding, loading and starting an operating system. Many computer systems also allow these operations to be initiated by a software command without cycling power, in what is known as a soft reboot, though some of the initial operations might be skipped on a soft reboot. A boot loader is a computer program that loads the main operating system or runtime environment for the computer after completion of the self-tests.

The computer term boot is short for bootstrap or bootstrap load and derives from the phrase to pull oneself up by one’s bootstraps.The usage calls attention to the requirement that, if most software is loaded onto a computer by other software already running on the computer, some mechanism must exist to load initial software onto the computer. Early computers used a variety of ad-hoc methods to get a small program into memory to solve this problem. The invention of read-only memory (ROM) of various types solved this paradox by allowing computers to be shipped with a start up program that could not be erased. Growth in the capacity of ROM has allowed ever more elaborate start up procedures to be implemented.

On general purpose computers, the boot process begins with the execution of an initial program stored in boot ROMs or read in another fashion. In some older computers, the initial program might have been the application to run, if no operating system was used, or the operating system. In other computers, the initial program is a boot loader that may then load into random-access memory (RAM), from nonvolatile secondary storage (such as a hard disk drive) or, in some older computers, from a medium such as punched cards, punched tape, or magnetic tape, the binary code of an operating system or runtime environment and then execute it. If the boot loader is limited in its size and capabilities, it may, instead, load a larger and more capable secondary boot loader, which would then load the operating system or runtime environment. Some embedded systems do not require a noticeable boot sequence to begin functioning and when turned on may simply run operational programs that are stored in ROM.

3.What are features of windows 7, Mac OS X, UNIX, and Linux Operating Systems?

    1. Windows 7

Windows 7 is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops, netbooks, tablet PCs, and media center PCs. It was released to manufacturing on July 22, 2009, and became generally available for retail worldwide on October 22, 2009, less than three years after the release of its predecessor, Windows Vista. Windows 7’s server counterpart, Windows Server 2008 R2, was released at the same time. Windows 7 is succeeded by Windows 8.

Unlike Windows Vista’s many new features, Windows 7 was an incremental upgrade designed to work with Vista-compatible applications and hardware. Presentations given by Microsoft in 2008 focused on multi-touch support, an updated Windows shell with a new taskbar, referred to internally as the Superbar, a home networking system called HomeGroup,  and performance improvements. Some standard applications that have been included with prior releases of Microsoft Windows, including Windows Calendar, Windows Mail, Windows Movie Maker, and Windows Photo Gallery, are not included in Windows 7; most are instead offered separately at no charge as part of the Windows Essentials suite.

  1. Mac OS X

Mac OS X is a multitasking operating system available only for Apple computers.

  1. UNIX

–          multi-user
more than one user can use the machine at a time
supported via terminals (serial or network connection)

–          multi-tasking
more than one program can be run at a time

–          hierarchical directory structure
to support the organisation and maintenance of files

–          portability
only the kernel ( <10%) written in assembler
tools for program development
a wide range of support tools (debuggers, compilers)

  1. Linux

Linux is an operating system, a software program that controls your computer. Most vendors load an operating system onto the hard drive of a PC before delivering the PC, so, unless the hard drive of your PC has failed, you may not understand the function of an operating system.

An operating system solves several problems arising from hardware variation. As you’re aware, no two PC models (or models of other computers, for that matter) have identical hardware. For example, some PCs have an IDE hard drive, whereas others have a SCSI hard drive. Some PCs have one hard drive, others have two or more. Most PCs have a CD-ROM drive, but some do not. Some PCs have an Intel Pentium CPU, whereas others have an AMD K-6, and so on. Suppose that, in a world without operating systems, you’re programming a new PC application, perhaps a new multimedia word processor. Your application must cope with all the possible variations of PC hardware. As a result, it becomes bulky and complex. Users don’t like it because it consumes too much hard drive space, takes a long time to load, and – because of its size and complexity – has more bugs than it should.

Operating systems solve this problem by providing a single standard way for applications to access hardware devices. When an operating system exists, applications can be more compact, because they share the commonly used code for accessing the hardware. Applications can also be more reliable because this code is written only once, and by expert programmers, rather than by every application programmers.

As you’ll soon learn, operating systems do many other things as well; for example, they generally provide a file system so that you can store and retrieve data, and a user interface so that you can control the operation of your computer. However, if you think of a computer’s operating system as its subconscious mind, you won’t be far off the mark. It’s the computer’s conscious mind – applications such as word processors and spreadsheets – that do useful work. But, without the subconscious – the operating system – the computer would cease breathing and applications would not function.

4.What are various server operating systems?

Server operating systems include Windows Server 2008, UNIX, Linux, Solaris, and Netware. Windows Server 2008 is an upgrade to Windows Server 2003 and includes features of previous Windows Server versions. UNIX, like Linux, is a multipurpose operating system because it is both a stand-alone and server operating system. Solaris, a version of UNIX developed by Sun Microsystems, is a server operating system designed specifically for e-commeree applications. Novell’s NetWare is a server operating system designed for client/server networks.

5.What are the features of several embedded operating systems?

An embedded system is a computer system with a dedicated function within a larger mechanical or electrical system, often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal computer (PC), is designed to be flexible and to meet a wide range of end-user needs. Embedded systems control many devices in common use today.

Modern embedded systems are often based on microcontrollers (i.e CPUs with integrated memory and/or peripheral interfaces)  but ordinary microprocessors (using external chips for memory and peripheral interface circuits) are also still common, especially in more complex systems. In either case, the processor(s) used may be types ranging from rather general purpose to very specialised in certain class of computations, or even custom designed for the application at hand. A common standard class of dedicated processors is the digital signal processor (DSP).

The key characteristic, however, is being dedicated to handle a particular task. Since the embedded system is dedicated to specific tasks, design engineers can optimize it to reduce the size and cost of the product and increase the reliability and performance. Some embedded systems are mass-produced, benefiting from economies of scale.

Physically, embedded systems range from portable devices such as digital watches and MP3 players, to large stationary installations like traffic lights, factory controllers, and largely complex systems like hybrid vehicles, MRI, and avionics. Complexity varies from low, with a single microcontroller chip, to very high with multiple units, peripherals and networks mounted inside a large chassis or enclosure

6.What is the purpose of several utility programs?

Utility Software is essentially what takes care of your computer system. Utility Software consists of but is not limited to the following: Disk cleaner – Finds files that are not in use anymore, or may have never been in use that take up a lot of space on the hard drive. Defragmenter – Locating the files that may be broken and therefore not completely functionary to the system and grouping them together, placing them in a different area of your computer’s hard drive. Checker – Similar to cleaners, disk checkers scan your computer to see if you have any files that are corrupt or unusable due to incorrect saving, to create a more capable computer system. Anti-virus system – A utility that scans your computer for threats or viruses that have made their way on to your computer, whether it’s from visiting un-trusted websites or downloads. It quarantines any viruses and allows you to delete them how you wish. Space analyzer – This option shows you how much of your hard drive is being used and by what. It gives you the size of each document, folder, and systems and groups it all together to also show you how much space is not being used. Backups ” Backing up a system is handy to do and very recommended for important files. It saves or copies on your computer system and can restore all or portions of a document or system in the case of a system error, or improper saving of a document. Networks – This utility will check your computer’s connectivity to one or more networks. It offers ways of repairing lost connections as well as keeps a record of networks you may have used. All of these put together are used to optimize your computer and make it work in the most efficient way possible.

assignment chapter 7

lecturer : Mr. Tri Djoko Wahjono, Ir.M.Sc

1.       How Are Storage Devices Different from Storage Media?

  • Storage device refers to the apparatus for recording computer data. Examples are the RAM, floppy drives, ZIP drives, and other disks drives. While, storage media are the materials on which data are written and stored or a devices that store application and user information. Examples are the floppy disks, optical discs, hard disks, etc.
  • A storage device is the computer hardware that records and/or retrieves items to and from storage media.

 2.       What Are the Characteristics of an Internal Hard Disk?

hard disk drive (HDD)is a data storage device used for storing and retrieving digital information using rapidly rotating disks (platters) coated with magnetic material. An HDD retains its data even when powered off. Data is read in a random-access manner, meaning individual blocks of data can be stored or retrieved in any order rather than sequentially. An HDD consists of one or more rigid (“hard”) rapidly rotating disks (platters) with magnetic heads arranged on a moving actuator arm to read and write data to the surfaces.

The primary characteristics of an HDD are its capacity and performance

  • The capacity of a hard disk

Is determined from whether it uses longitudinal or perpendicular recording, the number of platters it contains, and the composition of the magnetic coating on the platters.

  • Performance
  • A.      Time to access data

The factors that limit the time to access the data on an HDD are mostly related to the mechanical nature of the rotating disks and moving heads. Seek time is a measure of how long it takes the head assembly to travel to the track of the disk that contains data. Rotational latency is incurred because the desired disk sector may not be directly under the head when data transfer is requested. These two delays are on the order of milliseconds each. The bit rate or data transfer rate (once the head is in the right position) creates delay which is a function of the number of blocks transferred; typically relatively small, but can be quite long with the transfer of large contiguous files. Delay may also occur if the drive disks are stopped to save energy.

Time to access data can be improved by increasing rotational speed (thus reducing latency) and/or by reducing the time spent seeking. Increasing areal density increases throughput by increasing data rate and by increasing the amount of data under a set of heads, thereby potentially reducing seek activity for a given amount of data.

B.      Seek time

Seek time has continued to improve slowly over time. Some desktop and laptop computer systems allow the user to make a tradeoff between seek performance and drive noise. Faster seek rates typically require more energy usage to quickly move the heads across the platter, causing louder noises from the pivot bearing and greater device vibrations as the heads are rapidly accelerated during the start of the seek motion and decelerated at the end of the seek motion. Quiet operation reduces movement speed and acceleration rates, but at a cost of reduced seek performance.

C.      Latency

Latency is the delay for the rotation of the disk to bring the required disk sector under the read-write mechanism. It depends on rotational speed of a disk, measured in revolutions per minute (rpm). Average rotational latency is shown in the table below, based on the statistical relation that the average latency in milliseconds for such a drive is one-half the rotational period.

D.      Data Transfer rate

HDD data transfer rate depends upon the rotational speed of the platters and the data recording density. Because heat and vibration limit rotational speed, advancing density becomes the main method to improve sequential transfer rates. Higher speeds require more power absorbed by the electric engine, which hence warms up more. While areal density advances by increasing both the number of tracks across the disk and the number of sectors per track, only the latter increases the data transfer rate for a given rpm. Since data transfer rate performance only tracks one of the two components of areal density, its performance improves at a lower rate.

3.       What Is the Purpose of Network Attached Storage Devices, External and Removable Hard Disks, and Hard Disk Controllers?

  • Network Attached Storage Device

NAS is useful for more than just general centralized storage provided to client computers in environments with large amounts of data. NAS can enable simpler and lower cost systems such as load-balancing and fault-tolerant email and web server systems by providing storage services.

File-level computer data storage connected to a computer network providing data access to a heterogeneous group of clients. NAS not only operates as a file server, but is specialized for this task either by its hardware, software, or configuration of those elements.

  • External and Removable Hard Disks

An external hard disk is a separate freestanding hard disk that connects with a cable to a USB or FireWire port on the system unit or communicates wirelessly. External hard disks have storage capacities up to 4 TB and more.

A removable hard disk can be inserted or removed from a built-in or external drive. Removable hard disks have storage capacities up to 1 TB

  • Hard Disk Controller

Controller consists of a special-purpose chip and electronic circuits that control the transfer of data, instructions, and information from a disk to and from the system bus and other components in a computer. A hard disk controller may be part of the hard disk on the motherboard, or it may be a separate

4.       What Are the Various Types of Flash Memory Storage? 

  • A solid state drive (SSD)

Typically uses flash memory to store data, instructions, and information. Data storage device using integrated circuit assemblies as memory to store data persistently. SSD technology uses electronic interfaces compatible with traditional block input/output (I/O) hard disk drives, thus permitting simple replacement in common applications.

  • A memory card

Is a removable flash memory device that you insert and remove from a slot in a computer, mobile device, or card reader or writer. Common memory cards include CompactFlash, Secure Digital (SD), Secure Digital High Capacity (SDHC), micro SD, microSDHC, xD Picture Card, Memory Stick, and Memory Stick Micro (M2).

  • A USB flash drive

Sometimes called a thumb drive, is a flash memory storage device that plugs in a port on a computer or mobile device.

  • An Express Card module

Is a removable device that it’s in an Express Card slots. Express Card modules can add memory, storage, communications, or other capabilities to a computer.

5.       What Is Cloud Storage, and What Are Its Advantages?

Cloud storage is a model of networked enterprise storage where data is stored in virtualized pools of storage which are generally hosted by third parties. Hosting companies operate large data centers, and people who require their data to be hosted buy or lease storage capacity from them or Internet service that provides storage for computer users.

Advantage of Cloud storages:

  • Companies need only pay for the storage they actually use, typically an average of consumption during a month. This does not mean that cloud storage is less expensive, only that it incurs operating expenses rather than capital expenses.
  • Organizations can choose between off-premise and on-premise cloud storage options, or a mixture of the two options, depending on relevant decision criteria that is complementary to initial direct cost savings potential; for instance, continuity of operations (COOP), disaster recovery (DR), security (PII, HIPPA, SARBOX, IA/CND), and records retention laws, regulations, and policies.
  • Storage availability and data protection is intrinsic to object storage architecture, so depending on the application, the additional technology, need effort and cost to add availability and protection can be eliminated.
  • Storage maintenance tasks, such as purchasing additional storage capacity, are offloaded to the responsibility of a service provider.
  • Cloud storage provides users with immediate access to a broad range of resources and applications hosted in the infrastructure of another organization via a web service interface.
  • Cloud storage can be used for copying virtual machine images from the cloud to on-premise locations or to import a virtual machine image from an on-premise location to the cloud image library. In addition, cloud storage can be used to move virtual machine images between user accounts or between data centers.
  • Many Cloud Storage providers offer free accounts which can be expanded through various techniques, which many people have started to take advantage of to get hundreds of gigabytes of free online storage.

6.       What Are the Characteristics of Optical Discs?

Is a flat, usually circular disc which encodes binary data (bits) in the form of pits (binary value of 0 or off, due to lack of reflection when read) and lands (binary value of 1 or on, due to a reflection when read) on a special material (often aluminum) on one of its flat surfaces. The encoding material sits atop a thicker substrate (usually polycarbonate) which makes up the bulk of the disc and forms a dust defocusing layer. The encoding pattern follows a continuous, spiral path covering the entire disc surface and extending from the innermost track to the outermost track. The data is stored on the disc with a laser or stamping machine, and can be accessed when the data path is illuminated with a laser diode in an optical disc drive which spins the disc at speeds of about 200 to 4,000 RPM or more, depending on the drive type, disc format, and the distance of the read head from the center of the disc (inner tracks are read at a higher disc speed). The pits or bumps distort the reflected laser light, hence most optical discs (except the black discs of the original PlayStation video game console) characteristically have an iridescent appearance created by the grooves of the reflective layer. The reverse side of an optical disc usually has a printed label, sometimes made of paper but often printed or stamped onto the disc itself. This side of the disc contains the actual data and is typically coated with a transparent material, usually lacquer. Unlike the 3½-inch floppy disk, most optical discs do not have an integrated protective casing and are therefore susceptible to data transfer problems due to scratches, fingerprints, and other environmental problems. Optical discs, which primarily store software, data, digital photos, movies, and music, contain microscopic pits (indentations) and lands (flat areas) in their middle layer. Optical discs commonly store items in a single track that spirals from the center of the disc to its edge. Like a hard disk, the ingle track is divided into evenly sized sectors.

  1. 7.       How Are the Various Types of Optical Discs Different?

There are numerous formats of optical direct to disk recording devices on the market, all of which are based on using a laser to change the reflectivity of the digital recording medium in order to duplicate the effects of the pits and lands created when a commercial optical disc is pressed. A CD-ROM, or compact disc read-only memory, is a type of optical disc that uses laser technology to store items Users can read the contents of standard CD-ROMs but cannot erase or modify their contents. Formats such as CD-R and DVD-R are “Write once read many” is a multisession disc on which users can record their own items, such as text, graphics, and audio, while CD-RW and DVD-RW are rewritable, more like a magnetic recording hard disk drive (HDD).

7.How Are Tape, Magnetic Stripe Cards, Smart Cards, Microfilm and Microfiche, and Enterprise Storage Used?

  • Tape

tape drive is a data storage device that reads and writes data on a magnetic tape. Magnetic tape data storage is typically used for offline, archival data storage. Tape media generally has a favorable unit cost and long archival stability.

  • A Magnetic Stripe Card

Is a type of card capable of storing data by modifying the magnetism of tiny iron-based magnetic particles on a band of magnetic material on the card. The magnetic stripe, sometimes called swipe card or magstripe, is read by swiping past a magnetic reading head. Such as credit card, entertainment card, bank card, or other similar card with a stripe that contains information identifying you and the card. A magnetic stripe card reader reads the information stored on the stripe.

  • A Smart Card

Any pocket-sized card with embedded integrated circuits.

Smart cards are made of plastic, generally polyvinyl chloride, but sometimes polyethylene terephthalate based polyesters, acrylonitrile butadiene styrene or polycarbonate. Since April 2009, a Japanese company has manufactured reusable financial smart cards made from paper. Smart cards can provide identification, authentication, data storage and application processing. Smart cards may provide strong security authentication for single sign-on (SSO) within large organizations.

  • Microfilm and microfiche

Microfilm is essentially 35mm photographic film that was used to take images of the pages of a book, a periodical volume or a newspaper.  The reel of film is then duplicated and sold to libraries.  Microfiche are flat sheets of photographic film about 4×6 inches in size. Reduce the amount of paper must handle, are inexpensive, and have the longest life of any storage media. Enterprises use computers, servers, and networks to manage and store huge volumes of data and information.

  • Enterprise Storage

Is the computer data storage designed for large-scale, high-technology environments of the modern enterprises. When comparing to the consumer storage, it has higher scalability, higher reliability, better fault tolerance, and much higher initial price. Some storage systems can provide more than 185 TB of storage, and optical disc servers hold hundreds of optical discs.

From the salesperson’s point of view, the four main enterprise storage markets are:

  • Online storage – large disk array solutions, minimizing access time to the data, and maximizing reliability;
  • Backup – off-line storage for data protection, with a smaller price per byte than online storage, but at a cost of higher average access time; often uses sequential access storage, such as tape libraries;
  • Archiving – technically similar to backup, but its purpose is long-term retention, management, and discovery of fixed-content data to meet regulatory compliance, litigation protection, and storage cost optimization objectives;
  • Disaster recovery solutions, used to protect the data from localized disasters, usually being a vital part of broader business continuity plan.

assignment chapter 6

lecturer : Mr. Tri Djoko Wahjono, Ir.M.Sc

1. What are the four types of output?

Output is data that has been processed into a useful form That is, computers process data (input) into information (output). The form of output varies, depending on the hardware and software being used and the requirements of the user. Monitors, traditional notebook computers, netbooks, Tablet PCs, portable media players, smart phones, digital cameras, and other mobile devices have screens that allow users to view documents, Web sites, e-mail messages, photos, videos, and movies. Many printers enable users to print color documents and photos. Through the computer’s speakers, headphones, or earbuds, users listen to sounds, music, and voice messages.

While working with a computer, a user encounters four basic types of output: text, graphics, audio, and video. Very often, a single form of output, such as a Web page, includes more than one of these types of output.

-Text: examples of output that primarily contain text are memos, letters, press releases, reports, classified advertisements, envelopes, mailing labels, and text messages. On the Web, users view and print many other types of text-based output. These include blogs, news and magazine articles, books, television show transcripts, stock quotes, speeches, and lectures.

-Graphics: many forms of output include graphics to enhance visual appeal and convey information. Business letters have logos. Reports include charts. Newsletters use drawings, clip art, and photos. Users print high-quality photos taken with a digital camera. Many Web sites use animated graphics, such as blinking icons, scrolling messages, or simulations.

-Audio: Users download their favorite songs from iTunes and listen to the music while working on the computer. Software such as games, encyclopedias, and simulations often have musical accompaniments for entertainment and audio clips, such as narrations and speeches, to enhance understanding. On the Web, users tune into radio and television stations and listen to audio clips, podcasts, or live broadcasts of interviews, talk shows, sporting events, news, music, and concerts. They also use the Internet to conduct real-time conversations with friends, coworkers, or family members, just as if they were speaking on the telephone.

-Video: as with audio, software and web sites often include video clips to enhance understanding. Vodcasts and video blogs, for example, add a video component to the traditional podcast and blog. Users watch a live or prerecorded news report, view a reply while attending a live sporting event, observe weather conditions, or enjoy a live performance of their favorite musician or musical group on a computer or mobile device. Instead of renting a movie, users can download movie content from a Web site for a fee and then watch the entire movie on a computer or mobile device. Attaching a video camera to the computer allows users to watch home movies on the computer. They also can attach a television’s antenna or cable to the computer and watch a television program on the computer screen.

2. What are the characteristics of various display devices?

A display device, or simply display, is an output device that visually conveys text, graphics, and video information. Information on a display device, sometimes called soft copy, exists electronically and appears for a temporary period.

Display devices consist of a screen and the components that produce the information on the screen. Desktop computers typically use a monitor as their display device. A monitor is a display device that is packaged as a separate peripheral. Some monitors have a tile-and-swivel base that allows users to adjust the angle of the screen to minimize neck strain and reduce glare from overhead lightning. With some, you can rotate the screen. Adjustable monitor stands allow you to adjust the height of the monitor. Monitor controls permit users to adjust the brightness, contrast, positioning, height, and width of images. Some have integrated speakers and/or a build-in Web cam.

Most mobile computers and devices integrate the display and other components into the same physical case. Some have touch screens. Traditional notebook computers and netbooks have a display that attaches with a hinge to the system unit. Tablet PCs are available with two types of displays: one that attaches with a hinge and one built into the top of the case. Some smart phone and digital camera displays also attach with a hinge to the device. On other smart phones and most PDAs, portable media players, digital cameras, and handheld game consoles, the display is built into the case. Newer vehicles integrate a display in the dashboard, enabling drivers to control audio, video, navigation, temperature, and other settings. Most display devices show text, graphics, and video information in color. Some, however are monochrome. Monochrome means the information appears in one color (such as white, amber, green, black, blue, or gray) on a different color background (such as black or grayish-white). Some mobile devices use monochrome displays because they require less battery power.

Two types of display devices are flat-panel displays and CRT monitors. A flat-panel display is a lightweight display device with a shallow depth and flat screen that typically uses LCD (liquid crystal display) or gas plasma technology. Types of flat-panel displays include LCD monitors, LCD screens, and plasma monitors. All flat-panel displays and some CRT monitors have a flat screen. The term, flat screen, means the screen is not curved.

3. What factors affect the quality of an LCD monitor or LCD screen?

An LCD monitor is a desktop monitor that uses liquid crystal display to produce images. These monitors produce sharp, flicker-free images. The quality of an LCD monitor or LCD screen depends primarily on its resolution, response time, brightness, dot pitch, and contrast ratio.

-Resolution is the number of horizontal and vertical pixels in a display device. For example, a monitor that has 1440 x 900 resolution displays up to 1440 pixels per horizontal row and 900 pixels per vertical row, for a total of 1,296,000 pixels to create a screen image. Recall that a pixel (short for picture element) is a single point in an electronic image. A higher resolution uses a great number of pixels and thus provides a smoother, sharper, and clearer image. As you increase the resolution, however, some items on the screen appear smaller. With LCD monitors and screens, resolution generally is proportional to the size of the device. For example, a widescreen 19-inch LCD monitor typically has a resolution of 1440 x 900, while a widescreen 22-inch LCD monitor has a resolution of 1680 x 1050. LCDs are geared for a specific resolution, called the native resolution. Although you can change the resolution to any setting, for optimal results, use the monitor’s native resolution setting.

-Response time of an LCD monitor or screen is the time in milliseconds (ms) that it takes to turn a pixel on or off. LCD monitors’ and screens’ response times range from 3 to 16 ms. The lower the number, the faster the response time.

-Brightness of an LCD monitor or LCD screen is measured in nits. A nit is a unit of visible light intensity equal to one candela (formerly called candlepower) per square meter. The candela is the standard unit of luminous intensity. LCD monitors and screens today range from 250 to 550 nits. The higher the nits, the brighter the images.

-Dot pitch, sometimes called pixel pitch, is the distance in millimeters between pixels on a display device. Text created with a smaller dot pitch is easier to read. Advertisements normally specify a monitor’s dot pitch or pixel pitch. Average dot pitch on LCD monitors and screens should .30 mm or lower. The lower the number, the sharper the image.

-Contrast ratio describes the difference in light intensity between the brightest white and darkest black that can be displayed on an LCD monitor. Contrast ratios today range from 500:1 to 2000:1. Higher contrast ratios represent color better.

4. What are various ways to print?

Until a few years ago, printing a document required connecting a computer to a printer with a cable. Although many users today continue to print using this method, a variety of printing options are available.

Today, wireless printing technology makes the task of printing from a notebook computer, smart phone, or digital camera much easier. Two wireless technologies for printing are Bluetooth and infrared. With Bluetooth printing, a computer or other device transmits output to a printer via radio waves. The computer or other device and the printer do not have to be aligned with each other; rather, they need to be within an approximate 30-foot range. With infrared printing, a printer communicates with a computer or other device using infrared light waves. To print from a smart phone, for example, a user lines up the IrDA port on the smart phone with the IrDA port on the printer.

Instead of downloading photos from a digital camera to a computer, users can print these digital photos using a variety of techniques. Some cameras connect directly to a printer via a cable. Others store photos on memory cards that can be removed and inserted in the printer. Some printers have a docking station, into which the user inserts the camera to print photos stored in the camera.

Finally, many home and business users print to a central printer on a network. Their computer may communicate with the network printer via cables or wirelessly.

5. How is a nonimpact printer different from an impact printer?

A printer is an output device that produces text and graphics on a physical medium such as paper. Printed information, called hard copy exists physically and is a more permanent form of output than that presented on a display device (soft copy).

A nonimpact printer forms characters and graphics on a piece of paper without actually striking the paper. Some spray ink, while others use heat or pressure to create images. Commonly used nonimpact printers are ink-jet printers, photo printers, laser printers, thermal printers, mobile printers, label and postage printers, plotters, and large-format printers.

-An ink-jet printer is a type of nonimpact printer that forms characters and graphics by spraying tiny drops of liquid ink onto a piece of paper. Ink-jet printers have become a popular type of color printer for use in the home. A reasonable quality ink-jet printer costs less than $100. Ink-jet printers produce text and graphics in both black-and-white and color on a variety of paper types. These printers normally use individual sheets of paper stored in one or two removable or stationary trays. Ink-jet printers accept papers in many sizes, ranging from 3 x 5 inches to 8 ½ x 14 inches. Available paper types include plain paper, ink-jet paper, photo paper, glossy paper, and banner paper. Most ink-jet printers can print photographic-quality images on any of these types of paper.

-A photo printer is a color printer that produces photo-lab-quality pictures. Some photo printers print just one or two sizes of photos, for example, 3 x 5 inches and 4 x 6 inches. Others print up to letter size, legal size, or even larger. Some even print panoramic photos. Generally, the more sizes the printer prints, the more expensive the printer. Many photo printers use ink-jet technology. With models that can print letter-sized documents, users connect the photo printer to their computer and use it for all their printing needs. For a few hundred dollars, this type of photo printer is ideal for the home or small business user. Other photo printer technologies are discussed later in the chapter.

-A laser printer is a high-speed, high-quality nonimpact printer. Laser printers are available in both black-and-white and color models. A laser printer for personal computers ordinarily uses individual 8 ½ x 11-inch sheets of paper stored in one or more removable trays that slide in the printer case. Some laser printers have built-in trays that accommodate different sizes of paper, while others require separate trays for letter- and legal-sized paper. Most laser printers have a manual feed slot where you can insert individual sheets and envelopes. Laser printers print text and graphics in high-quality resolutions, usually 1200 dpi for black-and-white printers and up to 2400 dpi for color printers. Laser printers usually print at faster speeds than ink-jet printers.

-A multifunction peripheral (MFP), also called an all-in-one device, is a single device that looks like a printer, scanner, copy machine, and perhaps a fax machine. A fax machine is a device that codes and encodes documents so that they can be transmitted over telephone lines. The documents can contain text, drawings or photos, or can be handwritten.

-A thermal printer generates images by pushing electrically heated pins against heat-sensitive paper. Basic thermal printers are inexpensive, but the print quality is low and the images tend to fade over time. Self-service gas pumps often print gas receipts using a built-in lower-quality thermal printer. Many point-of-sale terminals in retail and grocery stores also print purchase receipts on thermal paper.

-A mobile printer is a small, lightweight, battery-powered printer that allows a mobile user to print from a notebook computer, smart phone, or other mobile device while traveling. Barely wider than the paper on which they print, mobile printers fit easily in a briefcase alongside a notebook computer.

-A label printer is small printer that prints on an adhesive-type material that can be placed on a variety of items such as envelopes, packages, optical discs, photos, file folders and toys. Most label printers also print bar codes. Label printers typically use thermal technology.

-A postage printer is a special type of label printer that prints postage stamps. Some have built-in digital scales for weighing letters and packages. Postage printers allow users to buy and print digital postage, often called Internet postage, which means you purchase an amount of postage from an authorized postal service Web site. Each time a postage stamp prints, your postage account is updated. Although you can print Internet postage on an ink-jet or photo printer, postage printers can be more economical because they use thermal technology instead of ink catridges.

-Plotters are sophisticated printer used to produce high-quality drawing such as blueprints, maps, and circuit diagrams. These printers are used in specialized fields such as engineering and drafting usually are very costly. Current plotters use a row of charged wires (called styli) to draw an electrostatic pattern on specially coated paper and then fuse toner to the pattern. The printed image consists of a series of very small dots, which provides high-quality output.

An impact printer forms characters and graphics on a piece of paper by striking a mechanism against an inked ribbon that physically contacts the paper. Impact printers characteristically are noisy because of this striking activity. These printers commonly produce near letter quality (NLQ) output, which is print quality slightly less clear than what is acceptable for business letters. Companies may use impact printers for routine jobs such as printing labels. Impact printers are ideal for printing multipart forms because they easily print through many layers of paper. Factories, warehouses, and retail counters may use impact printers because these printers withstand dusty environments, vibrations, and extreme temperatures. Two commonly used types of impact printers are dot-matrix printers and line printers.

-A dot matrix printer produces printed images when tiny wire pins on a print head mechanism strike an inked ribbon. When the ribbon presses against the paper, it creates dots that form characters and graphics. Most dot-matrix printers use continuous form paper, in which thousands of sheets of paper are connected together end to end. The pages have holes along the sides to help feed the paper through the printer.

-A line printer is a high-speed impact printer that prints an entire line at a time. The speed of a line printer is measured by the number of lines per minute (lpm) it can print. Some line printers print as many as 3000 lpm. Mainframes, servers, or networked applications, such as manufacturing, distribution or shipping, often use line printers. These printers typically use 11 x 17- inch continuous-form paper.

6. What are ink-jet printers, photo printers, laser printers, multifunction peripherals, thermal printers, mobile printers, label and postage printers, and plotters and large-format printers?

– Ink-jet printers: An ink-jet printer is a type of nonimpact printer that forms characters and graphics by spraying tiny drops of liquid ink onto a piece of paper. Ink-jet printers have become a popular type of color printer for use in the home. A reasonable quality ink-jet printer costs less than $100. Ink-jet printers produce text and graphics in both black-and-white and color on a variety of paper types. These printers normally use individual sheets of paper stored in one or two removable or stationary trays. Ink-jet printers accept papers in many sizes, ranging from 3 x 5 inches to 8 ½ x 14 inches. Available paper types include plain paper, ink-jet paper, photo paper, glossy paper, and banner paper. Most ink-jet printers can print photographic-quality images on any of these types of paper.

-Photo printers: A photo printer is a color printer that produces photo-lab-quality pictures. Some photo printers print just one or two sizes of photos, for example, 3 x 5 inches and 4 x 6 inches. Others print up to letter size, legal size, or even larger. Some even print panoramic photos. Generally, the more sizes the printer prints, the more expensive the printer. Many photo printers use ink-jet technology. With models that can print letter-sized documents, users connect the photo printer to their computer and use it for all their printing needs. For a few hundred dollars, this type of photo printer is ideal for the home or small business user. Other photo printer technologies are discussed later in the chapter. Most photo printers are PictBridge enabled, so that you can print photos directly from a digital camera by connecting a cable from the digital camera by connecting a cable from the digital camera to a USB port on the printer.

-Laser printers: A laser printer is a high-speed, high-quality nonimpact printer. Laser printers are available in both black-and-white and color models. A laser printer for personal computers ordinarily uses individual 8 ½ x 11-inch sheets of paper stored in one or more removable trays that slide in the printer case. Some laser printers have built-in trays that accommodate different sizes of paper, while others require separate trays for letter-and legal-sized paper. Most laser printers have a manual feed slot where you can insert individual sheets and envelopes. Laser printers print text and graphics in high-quality resolutions, usually 1200 dpi for black-and-white printers and up to 2400 dpi for color printers. While laser printers usually cost more than ink-jet printers, many models are available at affordable prices for the home user. Laser printers usually print at faster speeds than ink-jet printers.

-Multifunction peripherals: A multifunction peripheral (MFP), also called an all-in-one device, is a single device that looks like a printer or a copy machine but provides the functionality of a printer, scanner, copy machine, and perhaps a fax machine. A fax machine is a device that codes and encodes documents so that they can be transmitted over telephone lines. The documents can contain text, drawings or photos, or can be handwritten. The features of these devices vary. Another advantage of these devices is they are significantly less expensive than if you purchase each device separately. If the device breaks down, however, you lose all four functions, which is the primary disadvantage.

-Thermal printers: A thermal printer generates images by pushing electrically heated pins agains heat-sensitive paper. Basic thermal printers are inexpensive, but the print quality is low and the images tend to fade over time. Self-service gas pumps often print gas receipts using a built-in lower-quality thermal printer. Many point-of-sale terminals in retail and grocery stores also print purchase receipts on thermal paper. Two special types of thermal printers have high print quality and can print at much faster rates than ink-jet and laser printers. A thermal wax-transfer printer generates rich, nonsmearing images by using heat to melt colored wax onto heat-sensitive paper. Thermal wax-transfer printers are more expensive than ink-jet printers, but less expensive than many color laser printers.

-Mobile printers: a mobile printer is a small, lightweight, battery-powered printer that allows a mobile user to print from a notebook computer, smart phone, or other mobile device while traveling. Barely wider than the paper on which they print, mobile printers fit easily in a briefcase alongside a notebook computer. Mobile printers mainly use ink-jet, thermal, thermal wax-transfer, or dye-sublimation technology. Many of these printers connect to a USB port. Others have a built-in wireless port through which they communicate with the computer wirelessly.

-Label printer: a label printer is a small printer that prints on an adhesive-type material that can be placed on a variety of items such as envelopes, packages, optical discs, photos, file folders, and toys. Most label printers also print bar codes. Label printers typically use thermal technology.

-Postage printer: A postage printer is a special type of label printer that prints postage stamps. Some have built-in digital scales for weighing letters and packages. Postage printers allow users to buy and print digital postage, often called Internet postage, which means you purchase an amount of postage from an authorized postal service Web site. Each time a postage stamp prints, your postage stamp prints, your postage account is updated. Although you can print Internet postage on an ink-jet or photo printer, postage printers can be more economical because they use thermal technology instead of ink catridges.

-Plotters and large-format printers: Plotters are sophisticated printers used to produce high-quality drawings such as blueprints, maps, and circuit diagrams. These printers are used in specialized fields such as engineering and drafting and usually are very costly. Current plotters use a row of charged wires to draw an electrostatic pattern on specially coated paper and then fuse toner to the pattern. The printed image consists of a series of very small dots, which provides high-quality output. Using ink-jet printer technology, but on a much larger scale, a large-format printer creates photo-realistic-quality color prints. Graphic artists use these high-cost, high-performance printers for signs, posters, and other professional quality displays. Plotters and large-format printers can accommodate paper with widths up to 98 inches because blueprints, maps, signs, posters and other such blueprints, maps, signs, posters and other such drawings and displays can be quite large. Some plotters and large-format printers use individual sheets of paper, while others take large rolls.

7. What are the uses and characteristics of speakers, headphones, and earbuds?

An audio output device is a component of a computer that produces music, speech, or other sounds, such as beeps. Three commonly used audio output devices are speakers, headphones, and earbuds. Most personal computers and mobile devices have a small internal speaker that usually emits only low-quality sound. Thus, many users attach surround sound speakers or speaker systems to their computers, including game consoles and mobile devices, to generate higher-quality sounds for playing games, interacting with multimedia presentations, listening to music, and viewing movies. Most surround sound computer speaker systems include one or two center speakers and two or more satellite speakers that are positioned so that sound emits from all directions.

When using speakers, anyone in listening distance can hear the output. In a computer laboratory or other crowded environment, speakers might not be practical. Instead, users can listen through wireless headphones or earbuds or plug the device in a port on the sound card, in a speaker, or on the front of the system unit. With headphones or earbuds, only the individual wearing the headphones or earbuds hears the sound from the computer. The difference is that headphones cover or are placed outside the ear, whereas earbuds or earphones rest inside the ear canal. Both headphones and earbuds usually include noise-cancelling technology to reduce the interference of sounds from the surrounding environment.

8. What are the purposes and features of data projectors, interactive whiteboards, and force-feedback game controllers and mobile devices?

A data projector is a device that takes the text and images displaying on a computer screen and projects them on a larger screen so that an audience can see the image clearly. For example, many classrooms use data projectors so that all students easily can see an instructor’s presentation on the screen. Some data projectors are large devices that attach to a ceiling or wall in an auditorium. Some operating systems allow projectors to be part of the network, which enables a presenter to operate remotely via a network connection. Others, designed for the mobile user, are small portable devices that can be transported easily. Two types of smaller, lower-cost units are LCD projectors and DLP projectors. An LCD projector, which uses liquid crystal display technology, attaches directly to a computer, and uses its own light source to display the information shown on the computer screen.

An interactive whiteboard is a touch-sensitive device, resembling a dry-erase board, that displays the image on a connected computer screen. A presenter controls the computer program by clicking a remote control, touching the whiteboard with special digital pen and eraser, or writing on a special tablet. Notes written on the interactive whiteboard can be saved directly on the computer. Interactive whiteboards are used frequently in classrooms as a teaching tool, during meetings as a collaboration tool, and to enhance delivery of presentations.

Force-Feedback Game Controllers and Tactile Output: Today’s joysticks, wheels, gamepads, and motion-sensing game controllers also include force feedback, which is a technology that sends resistance to the device in response to actions of the user. For example, as you use the simulation software to drive from a smooth road onto a gravel alley, the steering wheel trembles or vibrates, making the driving experience as realistic as possible. These devices also are used in practical training applications such as in the military and aviation. Some input devices, such as smart phone, include tactile output that provides the user with a physical response from the device. For examples, users may sense a bumping feeling on their hand while scrolling through a smart phone’s contact list.

9. What output options are available for physically challenged users?

For users with mobility, hearing, or vision disabilities, many different types of output devices are available. Hearing-impaired users, for example can instruct programs to display words instead of sounds. With the latest Windows operating systems, users also can set options to make programs easier to use. The Magnifier, for example, enlarges text and other items in a window on the screen.

Visually impaired users can change Windows settings, such as increasing the size or changing the color of the text to make the words easier to read. Instead of using a monitor, blind users can work with voice output via Windows Narrator. That is, the computer reads the information that is displayed on the screen. Another alternative for visually impaired users, is a Braille printer, which prints out information on paper in Braille letters.