The intranet should be implemented in phased. If a network is already in place, the steps essentially revolve around selecting services and software, the operating system and special tools for content creation. The existing databases and software applications may be integrated into the intranet. This calls for a proper plan to be prepared. The important step to implementation follows.

Planning: This step includes scope of services and facilities; mail, Web sites, home pages department-wise, personnel, administration of the site, layout of pages, connecting with the internet.

Subnets: If the number of services and clients is large, there may be many subnets. IP addressing plan should be worked out in detail.

Services and software: Server hardware platforms and the software that will be used on them for hosting mail and Web services need to be finalized. For intranet users, browsers and mail clients have to be standardized. A server platform, may host both mail and Web services. As the intranet load grows, this could be split into multiple-servers. Web server, mail server, print server, Domain Name Server (DNS), workflow applications etc could be implemented on different hardware systems.

Operating system: An operating system may be chosen from the following popular server operating systems: UNIX, Linux, Windows NT, NetWare, Mac OS, OS/2, and AS/400. The choice of operating system will determine the software requirements of the Web server, mail server etc. While UNIX was the operating system on RISC systems, non-Unix platforms are equally aggressive solutions now. The OS should be installed on the server, complete with the TCP/IP suite of protocols. Web services should preferably be implemented from the very beginning. IP addresses and subnet masks should be allocated. It is better to use TCP/IP addresses duly registered with InterNIC so that connection to the Internet at a future date avoids address conflicts.

Proxy Servers: If the intranet requirements include the users connected on it to share a single Internet dial-up connection on the network, a proxy server is essential. It is the proxy server that dials into the Internet connection and all the nodes access the Internet through it.

Content Creation Software: HTML editors, Web-enabled office productivity tools are essential on client machines which are equipped with browsers and email software.

Training: The users on mail and Web applications may require training for discussion group, mailing list server, converting existing documents and reports for the intranet, and making them available to all. Skills to create new contents using the office-suites, productivity tools, HTML editors etc are also required.

Existing Databases: Set up a group of programmers to study the existing databases, and to Web-enable them for intranet.

Web Publishing: The Web is like a magazine, and content creation is like Web publishing. The magazine is on the Web server, and is used by the employees of an organization who are on the intranet. The contents should be catchy, easy to access, and up-to-date. Web design and maintenance are the major issues on an intranet.

Electronic funds transfer (EFT) systems constitute a major form of electronic commerce system in banking and retailing industries. EFT systems use a variety of information technologies to capture and process money and credit transfers between banks and businesses and their customers. For example, banking networks support letter terminals at bank offices and automated teller machines (ATM). Banks may also support pay-by-phone services allowing bank customers to use their telephones as terminals to electronically pay bills. Major forms of EFT systems are outlined below.

Banking and financial payments:

• Large-scale or wholesale payments (e.g., bank-to-bank transfer)
• Small-scale or retail payments (e.g., automated teller machines and cash dispensers)
• Home banking (e.g., bill payment)

Retailing payments:

• Credit cards (e.g., VISA, MasterCard etc.)
• Private credit/debit cards (e.g., JC Penny Card)
• Charge cards (e.g., American Express)

Online electronic commerce payments:

• Token-based payment systems
• Electronic cash (e.g., CyberCoin)
• Electronic Checks (e.g., NetCheque)
• Smart cards or debit cards (e.g., Mondex Electronic Currency Card)
• Credit card-based systems
• Encryped credit cards (e.g., SSL, CyberCash, or SET encryption)
• Third-party authorization numbers (e.g., First Virtual)

Secure Electronic Payments on the Internet:

One of the most noticeable and controversial topics in the Internet commerce today is the security of Internet transactions. While the technological difficulties may be soluble, a less obvious problem is how to define standards to let all consumers and merchants do business with each other while satisfying security requirements of the financial institutions involved. 

When a user makes an online purchase on the Internet, his credit card information is vulnerable to interception by network sniffers-software that easily recognizes credit card number formats. Several basic security measures are used to solve security problems:

• Encrypting (code and scrambling) the data passing between the customer and merchant.
• Encrypting the data passing between the customer and the company authorizing the credit card transaction
• Taking sensitive information offline.

Many companies use the Secure Socket Layer (SSL) security method developed by Netscape Communicator that automatically encrypts data passing between user Web browser and a merchant’s server. However, sensitive information is still vulnerable to misuse once it is decrypted (decoded and unscrambled) and stored on a merchant’s server. So a digital wallet approach, such as the Cyber Cash payment system, was developed. In this method one can add security software add-on modules to the Web browser. This enables user’s browser to encrypt credit card data in such a way that only the bank that authorizes credit card transactions for the merchant gets to see it.

Another security mechanism is Secure HyperText Transfer Protocol (SHTTP). To ensure a secure conversation between a Web client and a server, SHTTP works by negotiating the type to encryption scheme used between client and server. SHTTP and SSL can both be used for improved security.

To Secure Electronic Transaction, or SET, is another ordinary for electronic payment safety. In this technique, e-commerce software encrypts a digital envelope of digital certificates specifying the payment details for each operation. SET has been agreed to by VISA, Master Card, IBM, Microsoft, Netscape, and most other commerce players. Therefore, SET is expected to become the dominant standard for secure electronic payments on the Internet.

Other electronic payment systems for example, micro-payment systems like CyberCoin and DigilatCash. These technologies create currency or digital cash, sometimes called e-cash, for making payments that are very small for credit card transactions. Authentication and the encryption techniques are used to create strings of data that can be handled like currency for making cash payments. For example, Web sites like ESPNET Sports Zone, and Rocket Science Games let users chat with superstars, Discovery Online, play various kinds of video games or download the desired video segments by using digital cash micro-payment methods.

A wide area network connects computers located across a wide geographical area. For example an organization may have its offices scattered over different cities and each office needs to share data with other offices. In this case computers and LANs of different sites may be connected by public communication facility (like telephone network) or private communication network to realize a WAN. A WAN for a particular organization is called enterprise-wide network. The Internet is a popular example of WAN as it connects thousands of computers and LANs around the world.

Intermediate devices like gateways and routers and transmission facilities like telephone and data networks, fiber optic links, satellites are generally used for realizing WANs. The major features of WANs are listed below.

• Multiple computers are connected together
• Computers are spread over a wide geographic area
• A WAN usually interconnects multiple LANs
• Communication links between computers are provided by telephone networks, public data networks, satellites etc.
• Links are of low capacity (that is low data rate)
• Bit error rate is higher (1 in 100,000) compared to that for a LAN.

Bandwidth: Speed and capacity of computers and communication networks can be classified by bandwidth. The speed and capacity of data networks are generally measured in bits per second (bps). Low speed local communication channels are typically used for transmission rates from 300 to 56000 bps, but can now handle up to several Mbps for ADSL connections. They are usually TUP lines commonly used for voice communications, but are also for data communications by PCs, video terminals and fax machines. SPT lines can be used for speed up to 100 Mbps for short distances. High speed broadband digital channels allow transmission rates from 256,000 bps to several billion bps; typically they are microwave, satellite transmission and fiber optic cables.

Switching: Switching techniques used for WAN are circuit switching, message switching and packet switching. Normal telephone service relies on circuit switching. In circuit switching a switch establishes and maintains a link between a sender and receiver until the communication session is completed. In message switching, a complete message is transmitted in a block from one switching node to another.

In packet switching a message is subdivided into groups called packets. In X.25 packet switching, packets are 128 characters long, while they are of variable length in frame relay packet switching. Frame Relay is considerably faster than X.25 and is used by many large companies for their wide area networks. ATM (Asynchronous transfer mode) is a fast emerging high speed cell switching network technology. An ATM system, using BISDN (Broadband Integrated Service Digital Network), organizes voice, video, and other data into fixed cells of 53 bytes and send them to their next destination. ATM networks are becoming popular for the faster high-capacity multimedia services for voice, video and other high speed applications. Currently available network technology with data rates for WAN are listed below.

Network Technologies	Typical Data Rate
DDN: Digital Data Network	2.4 kbps - 2 Mbps
PSN: Packet Switching Network	2.4 kbps - 64 kbps
Frame Relay Network	56/64 kbps - 2 Mbps
ISDN: Integrated Services Digital Network	64/128 kbps - 2Mbps
ATM: Asychronous Transfer Mode	25/155 Mbps - 2.4 Gbps

The computer organizing a transaction must identify its intended destination with a unique address. Every computer on the Internet has a 4-part numeric address, called the IP (Internet Protocol) address. The IP address contains routing information that identifies destination location. Each of the four parts is a number between 0 and 255, so an IP address looks like this: 108.64.125.116.

Computers have no trouble working with such numbers, but humans are not so skilled. Therefore, computers connected to the Internet use an address system called a Domain Name System (DNS), where and address uses words instead of numbers.

DNS address have two parts: an user name, followed by a domain that identifies the type of institution that uses the address, such as .com for commercial or .edu for schools, colleges, and universities. Microsoft’s DNS address is Microsoft.com and Google’s DNS address is google.com. Within the United States, the last three letters of the domain usually tell the types of institution. The following table lists the most common types.

Domains	Types of organization
.com	(Business) Commercial
.edu	Educatonal
.gov	US Government
.mil	US Military
.net	Gateway or host
.org	Other organization

Large institutions and big corporations may divide their domain address into smaller sub-domains. A business with many branches might have a sub-domain for each office. Sub-domains may be broken into even smaller sub-domains, like: du.bangla.net. Outside the United States, domains usually identify the county in which the system is located, such as .in for India, .jp for Japan, .ca for Canada or .fr for France. A geographic domain address may include a sub-domain. An example could be: www.telemagazine.ac.uk.

DNS and IP address identify individual computers. A single computer might have many users, each of whom must have an account. Some of the largest domains may have huge number of different user names. When a message is sent to a person that person’s user name is the address identifies the recipient. The standard format is: the user name first, “at” symbol @, and finally the DNS address. Therefore, Imran’s e-mail address might be: Imran@titas.com.

Electronic-mail:

The most common use of the Internet is for the e-mail. Anyone with an e-mail account can send messages to other users of the Internet. Most e-mail programs also permit users to attach data files and program files to messages. E-mail is not a live connection between the sender of a message and its recipient. There is always a delay between the sending time of a message and its arrival time at the distention. Sometimes that delay is just a few seconds, but it is always there.

When a message is sent the computer presses it to a post office server, which identifies the destination address and passes it through the Internet to a mail server, where the message is stored in a mailbox until the recipient looks for it. The sender computer creates the message and sends it to a local post office server. The post office server passes the message through the Internet to the recipient’s mail server which passes it to the recipient’s computer. E-mail programs generally combine the following features.

• A text editor for writing and editing messages.
• Arrangements for storing names and e-mail addresses.
• Ability to send messages to a post office server.
• Ability to get messages from a mail server.
• A manager that organizes and stores the sent and received messages.

There is an e-mail program included in Windows 98 and many others are available separately. One of the most popular e-mail programs is Eudora, which exists in versions for both Windows and Macintosh operating systems. Besides one-to-one, Internet e-mail is also used for one-to-many, in which the same message goes to a list of names.

The World Wide Web (the Web or WWW) was created in 1989 at the European Particle Physics Laboratory in Geneva, Switzerland. Originally it was created as a method for incorporating footnotes, figures, and cross-references into online hypertext documents in which a reader can click on a word or phrase in a document, and immediately jump to another file. The second file may be located on the same computer or anywhere else on the internet. The WWW organizes widely scattered resources into a seamless whole.

The Web browsers have changed the way people use the Internet. Web pages are now used to distribute news, interactive educational services, product information and catalogs, highways traffic reports, live audio and video, among many other things. Interactive Web pages permit users to consult databases, order products and information, and submit payment with a credit card or other account number.

The latest Web browsers, including Google Chrome, Mozilla Firefox, Netscape Navigator and Microsoft’s Internet Explorer, can open file viewers and other application programs automatically when they receive graphic images, audio, video, and other files. Users also can import live, interactive data (such as financial information that changes frequently) and executable programs from the World Wide Web.

The organization of the World Wide Web is built on a set of rules called HyperText Transfer Protocol (HTTP) and a page description language called HyperText Markup Language (HTML). HTTP uses Internet addresses in a special format called a Uniform Resource Locator, or URL. The format or URLs is: type: //address/path

Here type specifies the type of server in which the file is located. The address part is the address of the server, and finally the path is the location within the file structure of the server. As an example the URL for the IEEE membership renewal is: http://www.ieee.org/renewal

A document that uses HTTP is known as a Web page. A Web page contains information about a particular subject with links to related Web pages. Many Web sites contain a top-level home page that has pointers to additional pages with more information. For example, a university might have a home page with links to a campus guide, Telnet access to the library, and separate pages for individual departments and offices.

Thousand of new Web pages appear every day, but they are not always easy to find. The World Wide Web does not provide a basic structure for locating resources. To fill this gap, search tools are available online. One of them is Google, Whose URL is https://www.google.com. Google is an extensively directory with menu that lists millions of web sites, organized by topic and a search engine that looks for specified words in titles and addresses of the Web sites in the directories. Other popular search tools include InfoSeek, Lycos, Magellan, and Excite, to name a few.

A computer network is a system of interconnected computers. The computers of a network communicate with one another and share applications, data, voice and videos, and hardware components. There are three main types of computer networks, they are:

LAN: It provides high speed communication between computers situated in a limited area, normally within a building or a small area like a college/university campus. LANs are typically owned and managed by a single organization.

WAN: This network spreads over a large geographical region and may attach computers within a country or cover many countries. WANs may be provided by telegraph and telephone organizations, they may be private to a single association or they may be controlled by a group of organizations. Usually, WANs have been implemented using packet switching and circuit switching technologies. A WAN can link a number of LANs. The internet is a popular example of WAN.

MAN: These networks cover an area of a typical city or town. They offer a trouble-free and fast way to connection different sites of a society for exchange of information. Mans use technologies similar to LAN technologies.

Uses of Computer Networks:Computer networks provide many benefits. Major uses of computer networks are:

• Simultaneous access to programs and data.
• Sharing peripheral devices like printers, scanners etc.
• Personal communications using e-mail
• Aiding communication by teleconferencing and video-conferencing.
• Protecting information by account name and password.

Some Network Terminologies: Network Topology: Topology of a network describes the way the computers and the nodes of the network are interconnected. There are a number of possible topologies:

• Bus topology
• Star topology
• Tree topology
• Ring topology
• Mesh topology.

Links: The physical connections that connect the nodes are known as links. A link may be through a pair of wires, a coaxial cable, and an optical fiber or through a satellite. The data transmission rates of the links are expressed by kbps (kilo bits per second), Mbps (Mega bits per second), Gbps (Giga bits per second) or Tbps (Tera bits per second). Examples are 64 kbps, 2 Mbps and 2.4 Gbps etc.

Media: The most commonly used media for computer networks are twisted pair, co-axial cable and optical fibre. Wireless techniques include broad-cast radio waves, microwaves and infrared.

Network Protocols: Computers of a network must obey some rules when communicating with each other. This set of rules forms the protocol for a computer network. The structural set of modules that implements the communication functions is called protocol architecture. An example of common protocol architecture is the TCP/IP protocol suite.

Software controls the operations of computer networks. The software that manages the resources of the network is often called the network operating system. Services in LANS rely on network operating systems, such as Novell Netware, IBM OS/2 Warp Server, or Microsoft Windows NT Server. A server network operating system must meet stringent set of requirements than a client operating system such as Windows 98 or Mac Operating system. A variety of communication software packages are available for microcomputers, especially for Internet Web browsing, like Microsoft Explorer, Netscape Navigator, Microsoft Outlook etc. Several functions are commonly provided by communication software packages, examples are: access control, transmission control, network management, error control, security management etc.

Access control: it is responsible for establishing the connection between terminals and computers in a network. Access control activities include connecting links through modems, establishing communication parameters such as speed, mode and direction, automatic telephone dialing and redialing, logging on and off with appropriate account numbers.

Transmission control: This function allows computer and terminals to send and receive commands, messages, data and programs. Data and programs are usually transmitted in the form of files and thus this activity is also called file transfer.

Error control: Error control function involves detection and correction of errors. Communication software and processors detect errors in transmission by different methods, including parity checking and cyclic redundancy checks (CRC). Most error correction methods involve retransmission, in which a signal is sent back to the computer to retransmit the previous message which has been received with error.

Network management function: This function manages communication in a computer network. It also monitors network activity and the use of network resources by end users. Security management is required to protect a computer network from unauthorized access. Network operating systems, or other security programs, restrict access to the data files and other computing resources in networks. Data transmissions can also be protected encryption and authentication technique.

In addition to a file manager, operating systems also include utility programs that one can use to manage disks and files. The list of such programs is almost endless.

Disk Formatting: Disk formatting utility makes the disk ready to store data. Formatting creates a directory of the locations of each file called a file allocation table (FAT). When a user saves a file, the operating system stores it in a group of sectors, called cluster, the smallest storage unit the computer can address. To do so, it looks in the file allocation table for empty clusters and then stores the file in one of those locations. The address of the clusters where the file begins and the one where it ends are then listed in the file allocation table. When a user opens the file, the operating system uses those addresses to locate he clusters and open the file stored in them.

Fragmenting: When a user first uses a disk, data are laid down in a linear fashion. Each part of a file is stored in adjacent clusters. However, as a user begins to delete old files and add new ones, things begin to become less orderly, because fragments of files are scattered in clusters located in different areas on the disk. This file fragmentation shows the computer down because it takes longer for the drive to locate, save, and retrieve the fragmented files. To fix this problem, a user needs to regularly defragment or defrag the disk. This procedure is often overlooked by computer users, who then wonder why their system gets slower and slower as time goes by. In many eased, the system will even begin to misbehave; programs crash or files do not open. Often these problems can be fixed just by defragging the disk.

Disk scanning: A newly manufactured disk is not always perfect. Some areas of the disk may not be usable. The manufacturer scans the disk and electronically marks bad areas as unusable so that no data are stored there. As the user uses the disk, other areas may become bad. For this reason, a utility program is used to scan the disk at regular intervals to locate and mark any bad sectors. If this is not done, the operating system may store parts of a file in them and then the user will not be able to retrieve that part of the file. In addition, scanning finds and fixes problems with files. For example, when systems crash, parts of files may be left scattered on the disk and become lost. The disk scanning program locates these lost clusters and stores them together in a separate file. In some cases, a user can open these files and recover lost work.

File deletion and recycle bin: Many of the files created by users on a computer eventually become outdated and no longer needed. To remove these files from the disk, users delete them. On many newer operating systems, the procedure does not actually delete them from the disk. Instead, it moves them to a separate area of the disk called a recycle bin or trash can. If user decides later that she/he wants to recover the file, can open the recycle bin and restore it to the disk. When absolutely certain that the user will never need the files in the recycle bin; the user can make it empty. However, if a user ever deletes files, provided any subsequent commands did not place new files in the place on the disk where they are stored.

When files are saved, they are assigned file names so that users can identity them later. Filenames have two parts: A name, and an extension. One may think of them as first and last name. The name is chosen to identity the file later. For DOS, a user has to use limited number of characters for the file name. However, a user can use long, descriptive filename in newer operating systems.

The extension is separated from the name by a period. Its purpose is to identify the file format or the application that created it. For example, a .DBR extension means the file is a database and .doc often means a word processing document.

Folders: A folder contains related document together. A well planned file cabinet uses hanging folders to group associated documents. It a further breakdown is needed, manila folders are place in the hanging folders. It is simple then to locate and pull out the documents needed. The same is true of hard drives. To master computing, one needs to know the concept of folders and their use for grouping together related files. A folder is also known as directory.

Drives: Most of the computer systems have more than one drive. Drives are assigned letters for identification. For example, a drive into which user can insert a floppy disk may be drive A or B. A computer looks to hard drive called C when user turns it on. Additional drives might be D and E. As the member and type of drives vary from system to system, so does the letter or name of each.

Floppy drive	A & B
Hard drive	C
CD-ROM drive	D
Zip drive	E

Trees: A tree is one of the ways to illustrate the organization of folders on a drive. In this view, all folders branch off from the drive. If a folder contains other folders, those folders are shown as a second branch from the first.

When using a tree, one can expand and collapse the entire tree or any branch. This allows a user to alternate between a summary or the drive’s contents, and details of each file. On windows, the plus sign indicates that a branch has been collapsed and it contains hidden folders. The minus sign indicates that the branch has been expanded.

Paths: A user has to follow a "path" to get files stored in folders on a disk. For example, if a file named varsity.doc name Letters or drive C, the path to that folder is C:\Letters\ varsity.doc. If varsity.doc is in a folder named Imran, the path is C:\Imran\ varsity.doc. The drive specification in a path is C: and the folder’s name is separated from it by a backlash.

Path to a file in a folder: The backlash is also used when a user has folders within folders. If the Letters folder contained a folder names Delowar, the path to it would then be C:\Letters\Delowar\ varsity.doc.

Path to a file in a subfolder: In most cases, a user does not need to type paths. Most new programs and operating systems let users to use a mouse to open folders to find a file.

File managers: Operating systems include a separate program that a user can use to explore drives, folders, and files. There are a variety of these but they all allow users to display the folders on a drive arranged like a tree. Clicking any of the folders displays a list of its contents.

When browsers and search engines were first developed for the Web, people soon discovered they could locate and get to a document anywhere in the world more easily than they could locate and get to one on their own system. As a result, browser technology is now being put to use in file management. Microsoft’s Active Internet Platform technology allows users to browse documents as well as the Web. In fact, a document on a local hard drive looks the same as a page anywhere on the Web.

Search engines on the Web keep track of millions of documents by searching them out and listing words they contain in an index. When a user searches a word, the search engine looks it up in the index and lists the name and address of every document in which it can be found. A user can go to the document just by clicking its name. The search engines make looking for documents so easy that personal versions are available for users own system.

Operating Systems that run on desktop computers are the least powerful and least secure operating system. They are also the most familiar. Most of the people like to use Windows in their computer. They are very popular and easy to use. Three common types of operating systems are:

• Windows
• Apple’s System 8, or
• Rapidly fading DOS.

Operating System for Servers: Currently, computers in networks are connected to one another not directly but through powerful computers called services that provide security to the networks and route traffic from one network to another. These complicated tasks require special operating systems. These powerful operating systems are also used for tasks (such as engineering design, order processing, and payroll) critical to a company’s continued existence, called mission critical applications. Such tasks were previously run only on target mainframe computers. These powerful 32- or 64-bit operating systems are secure, multitasking, multithreading, and open. All now processes graphical user interfaces developed for then. All but OS/2 are portable in that they run on more than one type of microprocessor.

• Windows NT (NT stands for New Technology) is the fasted-growing server operating system. The upgraded version of NT is called Windows 2000.

• OS/2 (Operating System/2) competes with windows and is a powerful operating system but has had trouble catching on.

• UNIX a powerful operating system for server was originally developed at AT&T’s Bell Labs in 1973.

Operating Systems for Mainfarame: In the early days of computer, mainframe and minicomputers dominated the computing world, and each computer company developed its own operating system. For example, some IBM mainframe computers use an operating system called open VMS and Digital Equipment Corporation minicomputers use one called VMS. These companies developed not just their own operating systems but also the applications that ran on top of them. These are called proprietary system because they are all owned by a single proprietor. Because there were so many competing operating systems, it was hard to make computers talk to one another. Although costly, these operating systems are both powerful and secure and capable of handling a variety of tasks.

Handheld operating systems: Windows CE, visually similar to Windows 95, uses a small keyboard and a touch-sensitive screen.

Embedded operating systems: Generally, a microprocessor is used inside a small device such as a watch, and it needs an operating system. Such an operating system is stored in a memory chip instead of a hard drive and turns on instantly when the device is turned on.

The most important task of an operating system is to process commands and to provide coordination between different processing tasks. Here are details about multitasking, processing commands, multithreading, multiprocessor and miscellaneous tasks of an Operating System (OS).

Processing Commands: The operating system interprets instructions entered through the keyboard. When one uses an application program, the program’s commands are interpreted by the operating system. For example, one might open a document by clicking a button on the program’s toolbar. At another time the user might do so by dragging the file onto the application’s icon and dropping it. The operating system interprets these commands and copies the document on the disk of the computer.

Multitasking: Modern operating systems allow multitasking, that is to perform multitasks, at the same time with different programs. For example, one could download a large file from the Internet with one program, while editing a document with another. Older operating systems could run only one program at a time. Since most systems have only one microprocessor, they allow multiple programs to run by quickly switching back and forth between them. Although only one program is actually active at a time; the processor switches so fast that they all appear to be active. This process is called time-slicing or task-switching because it slices up the CPU’s time as it switches between the running applications. Today’s system use a form of multitasking called preemptive multitasking. In this type of multitasking access to the microprocessor is controlled so that one application cannot seize it and hold it for long a period. One application can “preempt” another application to get a fair share of the processor’s time.

Multithreading: Most applications process data and commands sequentially, i.e. when one task is finished they begin another. The application therefore follows a single thread from the beginning of a session to the end and individual operations are strung like beads on a necklace. A multithreaded operating system on the other hand lets application programs start and run two or more threads simultaneously. It is similar to multitasking within a single program. For example, one thread in a word processing program can be reading the pressed keys while a second thread displays data on the screen and a thread prints the document.

Multi-user Support: Some operating systems are designed so that many users can be connected to the system at the same time. Multi-user operating systems are also multitasking because the multiple users run their programs at the same time.

Multiprocessor Support: Some applications need huge processing power. For example, anyone doing forecasting, modeling, simulating, or computer aided design needs enormous computing power. Some operating systems support multiple processors – in some cases hundreds or even more.

Miscellaneous Tasks: In addition to the processing tasks discussed, an operating system also performs the following tasks:

• The operating system continually monitors the system and if it detects something wrong, it outputs an error message.
• The operating system ménages the use of memory and runs each program in its own protected space to that a problem with one program will not affect others.
• The operating system allocates peripheral devices for different tasks.
• To conserve power, power management cuts power at those times when it is not needed.
• Manages file stored on disks.

In system software we need to test, debug and diagnose various programs. Programs created by us are prone to error. It is not realistic to expect a newly created program to run correctly the first time. Before a program can be put into productive use it must be debugged. A bug is a defect or imperfection in a program. In the context of programming it is an error in a program that is responsible for undesirable results. Testing or a program involves validation of program design. Thus testing involves data that are intentionally used to reflect the worst-case situations.

In order to assist the programmer in locating and rectifying errors or bugs in programs, several tools are available. These tools could be hardware aids such as logic analyzers or software aids such as debug programs. A debug program is loaded into the memory with the object program that is to be debugged. If errors occur during run, the debug program is activated to identify, locate, and correct the error. A debug program generally includes several features that aid the programmer in debugging tasks. Some of the common features are described below.

Display Register Contents: This feature allows the programmer to check contents of certain registers of the CPU during the execution of a program. The contents of the registers can be printed or displayed on appropriate devices. It is also possible to modify the contents of some registers if necessary.

Display/Replace memory Contents: The programmer can access the contents of a memory location and display it. The contents can then be modified if necessary.

Memory Dump: This feature makes it possible to print the contents of a group of memory locations. Thus a programmer can view the contents of desired memory location and determine accuracy of data.

Output Memory Content: The contents of a memory are transferred and stored in some other mass storage devices such as disks or magnetic tapes.

Breakpoints: Breakpoints are interrupts in the object program. They are used to examine the current status of certain critical CPU registers, memory locations, or I/O ports. When the execution of the object program reaches a breakpoint; its execution is temporarily halted. The debug program then allows the programmer to examine and alter the contents of the selected register, memory locations, or I/O ports to correct errors.

Disassembly: This is the servers of the assembly process. The operation consists of reading out the contents of the program memory into assembly language.

It is actually good news for all windows 8 users. You can enable the Dot net for all version of Windows 8 X86 and X64 OS. We made a file to perform this task easily. We have tested this file on 16 windows 8 operating system. We uploaded this file on "amonshare". Download it from there. Click on the free link to get it without any cost.

• Go to the Strat menu and type cmd
• Click Right button on cmd
• Then click on the run as administrator
• Copy the below command and paste it in cmd 

You have done successfully. Just enjoy…

If you are using windows 8 operating system and want to turn off the programs which are automatically opening on starting the windows 8, you can follow this procedure. Windows 8 is actually a popular operation system (OS). But to run this operating system you need to have a quality PC. Or it takes more time to open or shut down your computer. You can disable or turn off the unnecessary programs from the Startup option of your machine. It helps to run or open your PC quickly. Generally avast antivirus page, MSDN home page, IDM (Internet Download Manager) are the automatic opening programs in the Startup option of windows 8. You may try many ways to find a setting related option to perform this task but couldn't find it till easily. You can use several methods to do this task.

Method one:

• This method can be applied for win XP also.
• Open run command of your computer (keyboard shortcut Windows Key + R)
• Type >> msconfig
• A dialogue box will be opened with tabs services>>Startup etc.
• Now you should select the Startup tab
• Under that tab place your programs like MSDN home page, IDM, avast antivirus homepage etc.
• After that unchecked the check box.
• Click apply>> than OK
• Just restart your system and enjoy.

Method two:

Open the task manger using a right click in the left side of your computer. Look at the picture

Systems software refers to programs that assist the users to generate, debug, test, modify application programs, and then to executive them. These programs are generally written y computer manufacturers or software developers. The system programs can be used by different users and different application programs. The programs of system software can be grouped into:

• Operating system
• Language translators
• Utiltiy programs

The most important component of system program is the operating system. It is a collection of program modules. Collectively they manage all the hardware, provides user - interface and some other user facilities. Other system programs include language translators (i.e. assembler, compiler, and interpreter), text editors and some utility programs

An operating system is a software system. It acts as an interface between a user of a computer and the computer hardware. The operating system provides an environment in which a user may execute programs. The goals of an operating system are to:

• Make the computer system convenient for user
• Make efficient use of the computer hardware.

The operating system controls and coordinates the use of the hardware for different application programs. The basic resourced of a computer system are provided by its hardware, software and data. The operating system provides the means for the proper use of these resources in the operation of the computer system.

An operating system is an important part of a computer system. A computer system can be viewed to have four components:

• Hardware (CPU, memory, I/O devices etc.)
• Operating system
• Applications programs (compilers, database systems, video games, business programs etc.)
• Users (People, machines or other computers)

The role of BIOS: 

When starts, the computer system has no idea what drives it has and cannot even load its operating system. To solve this problem, a computer users the Basic Input/Output System (BIOS) to turn it on. This small program is permanently stored in a read-only memory (ROM) chip. Science it is a small program embedded in a chip, it occupies a place between the software and hardware. For this reason it is often called firmware. BIOS performs a number of important functions. It interprets key strokes, displays characters on the screen, handles communication through the computer’s ports, and tests the system while turning it on.

When a computer is turned on, the CPU hands over control to the BIOS, and the BIOS runs the power on self test or POST makes sure that all chips on the system board works well. Results of such tests are shown on the monitor at the time of turning on. Finally when the BIOS finds the operating system, in hard disk or floppy disk, it hands over control to the operating system.

Language Translators:

Machine language: The machine language is written in words comprising of 1s and 0s. Computers execute commands on instructions in machine language; programming in machine language has the following disadvantages:

• The program must be written in machine language
• Entering machine language program is a tedious process
• Error detection and correction is tedious and consumes much time
• Programs written in machine language for a specific machine cannot be used for another type of machine.

Assembler: Programming in assembly language is easier than programming in machine language. The programmer is required to write a source code for each instruction in the program and the assembler translates it to machine language. The programmer maintains total control of the computer operation. Assembly language offers the greatest degree of efficiently in operation and execution of programs.

Many shortcomings of machine language programming are overcome by programming in assembly language. Assembly instructions of a computer have mnemonics associated with them. The assembly program is written using these mnemonics. Assemblers are programs that translate assembly level codes into equivalent machine codes. For programming in assembly language, it is not necessary to write programs in absolute binary, octal or hexadecimal notations.

Compiler and Interpreter: High level languages are widely used. They have been developed to enable the users to program the machines in a language similar to the language of the users. For example BASIC, Pascal, C and Java use scientific notations and subroutines in programming formats that are similar to mathematical formulas and equations. On the other hand, COBAL contains business jargons widely used in business.

A Compiler is a program that translates programs written in high level language into machine language. A programs written by a programmer in a high level language, is called a source program. The source program when converted into machine language by a compiler is referred to as an object program. Unlike the assembler, the compiler generates several machine language instructions for each source statement. A compiler can be made to interface with several different computers. It is not written for any specific computer. A user can write programs that can be adapted to several computing systems. Thus, the user can formulate problems efficiently without precise knowledge of computer architecture. Compilers are complex programs compared to assemblers and they require more storage space than assemblers. An assemblers or a compiler produces the object program, which is loaded into the computer memory before execution.

An interpreter is a translator program that differs from the assembler or the compiler on several significant points. The interpreter does not prepare an object program. It translates and immediately executes each instruction of the source program. Thus an interpretive language is also an interactive language; it enables the user to load one instruction into the computer at a time and have it translated and executed. This process allows the programmer to check the results immediately. The interpreter is also a debugging tool and is useful during the program development stage. In the interpretive mode the execution time of the program is extended, but the program developmental effort and the program development time are decreased.

Comparison of Compiler and Interpreter:

Compiler	Interpreter
Compiler prepares an object program from source program	Interpreter translates and immediately executes each instruction of the source program
Debugging is complex and time consuming	It is a debugging tool and is useful during program developing stage
Lower execution time	Higher execution time
Requires higher program development effort and time	Requires less program development effort and time

Text Editor: While developing a program, it is often necessary to edit it. Editing involves making corrections or modifications to instructions, deletions and additions of instructions, re-sequencing instructions etc. A special program called editor greatly simplifies the editing tasks. An editor enables the user to retain the program in the memory and modify it as required. A portion of the memory, called buffer, is reserved for editing. Lines of instruction are entered from an external I/O device and stored in the buffer for editing by the editor. The edited text can be printed by a printer or recorded on suitable I/O devices.

You may change the screen resolution of your computer for any requirement. Did you change the screen resolution of your Android/Tabled? There is a difference between two of them. If anybody increases the resolution of his computer then the text, icon, app etc become smaller. But after increasing the density of Android/Tabled the icon, text, app etc become larger.

For the Screen Resolution of Android/Tabled the density setting is needed to change. Simply we can say that the DPI (dots per inch) is changed. It is known to all that the default DPI of Android/Tabled varies according to the different devices. For example: 120, 240, 320, 480…

When you decrease the DPI then the text, icon, app, widget etc. become smaller and after increase the DPI these look larger than before. Most of the user wants to change the screen resolution of their Android/Tabled. Because it increases the screen performance of the device. To make enough space in the home screen during the time of playing video games it is needed to increase the resolution. At that time high resolution is needed.

The accurate value of DPI (dots per inch) could not be measured. It depends on your device. The display setting which perfectly fit for your Android/Tabled is the accurate DPI of your device. You may try 2-3 setting. Somebody change the DPI from 120 to 90/100, 240 to 120/180/190, 320 to 240/180. But remember that if you do not set it accurately some app may be crashed. 

How to change density: You can use two processes to change the density of the device.

With app: It is a simply process. We use here the LCD Density Changer app. At first you need to download it. Then install this app in your device. Now change the density value and click the change button. After restarting the device you will see the changed screen. This process is very helpful for the new user. Just remove the battery to get default setting if any problems occurred.

With build.prop edit: It is also a easy process. Just download it from here. Install in your device. Then alter the density value of qemu.sf.lcd_density. Save and restart your device.

Today I am going to write how to delete all Junk files and make faster your Windows 7 operating system without using any software. Generally we use various software to make faster and speedy of our computer. Low speed of computer is really boring to operate it. The user of Windows-7 operating system can increase the speed of his PC without using any software. You may know that junk files reduce the speed of your PC. So it is better to remove all of these files time to time. Here is a full procedure to delete junk file from Windows-7 operating system without installing any third party software in your computer. 

• At first go your Desktop screen and using Right Click create a Text Document

• Type the below code in this folder. You can copy the code from here and past in the text document

• In the above code you can see a word "IMRAN". Just replace it with your computer name. To see the name go to the start bar option of your computer.

• Now save the file as a name " speed_up.bat". [file->save as->speed_up.bat]

• You can keep this file in the Desktop or any other folder in your computer.

• The use of this program is very easy. Just Double click the file and delete the entire JUNK file from your computer.

If you want to use any software to perform this task you can do it. But it takes the space in your hard drive and all of the software does not work properly. I follow this process. Just make a speed_up.bat file and use it to increase the speed of your PC. It is very helpful and does not take space in RAM CPU.

Every computer system has a unit whose primary purpose is to process data. This unit is the control centre of the entire computer system. It accepts data from input devices, processes data, and sends results to the printer or other output devices under control of a stored program. This unit is referred to as the microprocessor in a microcomputer and the central processing unit (CPU) in large computer systems. Both units perform basically the same functions.

Function of Microprocessor:

The microprocessor is an electronic device. It is the heart and brain inside every microcomputer. This tiny chip of silicon determines the speed and power of the entire computer by handling most, if not all, of the processing of a microcomputer. Functions of a microprocessor can be summarized as follows:

• The processor first fetches an instruction from the main memory.
• The instruction is then decoded to determine what action is required to be done.
• Based on instruction the processor fetches, if required, data from main memory or I/O module.
• The instruction is then executed which may required performing arithmetic or logical operation on data.
• In addition to execution, CPU also supervises and controls I/O devices. If there is any request from I/O devices, called interrupt, the CPU suspends execution of the current program and transfers control to an interrupt handling program.
• Finally, the results of an execution may require transfer of data to memory or an I/O Module.

Organization of a Microprocessor:

The major components of Microprocessor are an arithmetic/logic unit (ALU) and control unit (CU). The ALU performs the actual computation or processing of data. The control unit controls the movement of data and instructions into and out of the CPU. The internal CPU bus is needed to transfer data between the various registers and the ALU. The ALU operates only on data in the internal CPU memory. The registers in the CPU serve two functions:

• User-Visible Registers: These registers enable the program to minimize main-memory references by optimizing use of registers.
• Control and Status Registers: They are used to control the operations of the CPU and to control the execution of Programs.

User-Visible Registers:

User-visible registers can be characterized in the following categories:

• General purpose registers
• Data registers
• Address registers
• Condintion code registers

General-purpose registers can be assigned to a velocity of functions by the programmer. A general-purpose register can contain the operand for any opcode. This provides true general-purpose register use. However, there are restrictions. There may be dedicated registers for floati0gn-point operation.

General-Purpose registers can be used for addressing functions. In other cases, there is a fractional or clean separation between address registers and data registers, Data registers may be employed only to hold data and cannot be used in the control of an operand address. Address registers may be somewhat general-purpose, or they may be devoted to a particular addressing mode, some examples are:

1. Segment Pointers: A segment register holds the address of the base of a memory segment. There may be multiple registers; for example, one for the operating system and one for the current process.
2. Index Registers: These are used for indexed addressing and may be auto indexed.
3. Stack Registers: Normally the stack is in memory and there is a dedicated register that points to the top of the stack. This allows push, pop, and other stack instructions.

A final category of registers which is minimum partly visible to the user holds condition codes or flags. Condition codes are bits set by the Central Processing Unit (CPU) as the result of operations. For example, an arithmetic or logical function may construct a positive, negative or zero result or an overflow. In addition to the result, it may consequently be checked as element of a conditional branch operation.

Condition code bits are gathered into one or more registers. Generally, they shape part of a control register. Usually, instructions of the machine permit these bits to be read, but they cannot be changed by the programmer.

Control and Status Registers:

A variety of CPU registers control the operation of the CPU. Most of these are not visible to the user. A reasonably complete list of register types, with brief descriptions are presented here. The following four registers are essential for instruction execution:

• Program Counter (PC): Contains the address of an instruction to be fetched.
• Instruction Register (IR): Contains the instruction most recently fetched.
• Memory Address Register (MAR): Contains the address of a location in memory.
• Memory Buffer Register (MBR): Contains a word of data to be written to memory or the world most recently read.

The program counter contains an instruction address. Typically, the program counter is updated by the CUP after each instruction fetch and thus, it always points to the next instruction to be executed. A branch or skip instruction modify the contents of the PC. The fetched instruction is loaded into an instruction register, where the opcode is analyzed. Data are exchanged with memory using the MAR and MBR. In a bus-organized system, the MAR connects directly to the address bus, and the MBR cornets directly to the data bus. User-visible registers, in turn, exchange data with the MBR.

The four registers mentioned above are used for the movement of data between the CPU and memory. Within the CPU, data must be presented to the ALU for processing. The ALU may have direct access to the MBR and user-visible registers. Alternatively, there may be additional buffer registers at the boundary to the ALU; these registers serve as input and output registers for the ALU and exchange data with the MBR and user-visible registers.

All CPUs includes a register or set of registers, often known as the program status word (PSW) that contains status information. The PSW typically contains condition codes plus other status information. Common fields or flags include the following:

• Sign: Contains the sign bit of the result of the last arithmetic operation.
• Zero: Set when the result is 0.
• Carry: Set if an operation resulted in carry (addition) into or borrow (subtraction) out of a high-order bit.
• Equal: Set if a logical compare result in equality.
• Overflow: Employed to point toward arithmetic overflow.
• Interrupt Disable or Enable:  Applied to disable or enable interrupts.
• Supervisor: Indicates where the Central Processing Unit is executing in administrator or user mode. Certain privileged instructions can be performed only in supervisor mode, and certain areas of memory can be accessed only in supervisor mode.

In addition to the PSW, there may be a pointer to a block of memory containing additional status information. In machines using vectored interrupts, an interrupt vector register may be provided. If a stack is used to implement certain function (e.g., subroutine cell), then a system stack pointer is needed. A page table pointer is used with a virtual memory system. Finally, registers may be used in the control of I/O operations.

In addition to the above components modern microprocessors may also have the following components:

• Integer unit (iu): To handle the integer operation efficiently.
• Floating point unit (fpu): To perform floating point operations.
• Memory management unit (mmu): This unit handles run-time memory management problems to enhance performance.
• Data cache and instruction cache: These are also called bult-in cache. The built-in cache is a fast primary memory.

It is also noted that currently some microprocessors may have a special component for a specific purpose, for instance multimedia. Some processors have more than one ALU unit to enhance performance. Finally, it is essential to say that the components of a microprocessor may change or new components may be incorporated in the future.

Computer has various peripheral devices such as: modem, vision systems, speech recognition and voice response devices, terminal etc. These parts make a computer very important and attractive instrument in our daily life. Using various peripheral devices of computer we can do many essential tasks easily.

Terminal: 

A terminal is a popular input/output device. Terminals are used for two-way communications with a CPU or with other terminals a few feet or thousands of miles away. With the aid of a terminal, a user can access computers around the world. Terminals, also called workstations, allow a user to interact with a computer. It uses a keyboard to enter data and a cathode ray tube (CRT) screen, or monitor, for displaying data. Because data must be keyed into these devices one character at a time, the possibility of error is high and the data transmission rate is very low; thus limiting the use of terminals to small-volume input and inquiries only. Some of the functions that can be performed using terminals are described below.

Messaging: The communication of information from one terminal to one or more remote terminals.

Data Collection: Data are received by terminals and recorded on secondary storage media for subsequent processing. This eliminates needs to record the information on a source document and then to key the information from the source document into a computer.

Inquiry or transaction processing: Data stored in central data files can be accessed from remote terminals for updating or to determine answers to inquiries about information stored in these files. The system employed by most airlines to maintain and update flight information is an example of such a function.

Remote job processing: Programs can be received from remote terminals directly to a CPU for processing. After execution, the result can be transmitted back to the terminal or to other terminals for output.

Graphic display and design: Data ban be displayed in graphic form, and can also be manipulated and manipulated and modified. Interactive graphic displays, from simple vides games displayed on a television set to sophisticated computerized systems, provide complex designs and three-dimensional displays.

Terminals are available with features to suite the multitude of applications to which they are applied. In general three broad types of terminals are: dumb, smart and intelligent.

Speech Recognition and Voice Response Devices:

Speech recognition devices were introduced in the early 1970s. Typically, these systems contain a database of stored voice patterns. The database of voice patterns in generally stored in a recognition unit or in secondary storage. A microphone, attached to the keyboard or recognition unit, records the spoken word patters. A build-in microprocessor then compares words with the stored patterns and transmits the result of the comparison to a computer for processing. A sentence must be spoken as a serried of Speech recognition devices are generally used in situations where access to a switch is not possible or where a user’s hands are otherwise occupied.

Because voice patterns vary greatly from person to person, most speech recognition services are speaker-dependent and must be fine-tuned to each operation. This is generally accomplished by having the operator speaks each of the words or digits to be stored in the recognition unit dictionary several times. An average of the spoken voice patterns is taken and stored as the standard for future voice communications.

Speaker-independent systems are less common and have a very restricted vocabulary: generally then digits and “yes” or “no” response. Despite their restricted vocabulary, speaker-independent systems are widely usable since they do not have to be fine-turned but can be understood by anyone. Clearly, speaker-independent systems are more desirable than speaker-dependent systems. Expense, large database requirements and the limitations or current technology have made the development of voice recognition systems slow. Manufactures are beginning to offer sophisticated speech recognition devices for the popular microcomputer.

One of the strongest impacts made on the use of voice response has come from the manufacturers of microcomputers. The pricing and availability of voice response units are economically feasible for even the smallest concern. Voice response is no longer an isolated discipline but another among the multitude of computer output techniques.

Vision Systems:

This system utilizes a digitizer, camera, computer, and a technique termed as image processing. Image processing is concerned with digitizing and storing of computer-processed images and with pattern recognition.

Familiar examples of computer-processed images are: computer generated digitized portraits at amusement parks, computer-produced special effects in movies, digitized images of Jupiter and Saturn beamed from image processors of spacecraft to earth etc. All these examples have one thing is common, that is to digitize an image. In a visual system, all images that must be recognized or interpreted are digitized and stored in a database. Only after the database has been established, the visual system can be applied to pattern recognition. Pattern recognition, the process of interpreting images, begins when the system digitizes the image of the object to be interpreted. The digitized image is then compared to those in the database to determine a probable match. As it is unlikely that a perfect match will be achieved, there is always a small possibility or error.

Modem:

A modem is the bridge between digital and analog signals. It converts digital data into analog signals by varying or modulation an electrical wave, a process known as modulation. Modulation is carried out for sending digital data thorough analog telephone system. On the receiving end of a phone connection, a modem does just the opposite. It demodulates the analog signals back into digital code. The two terms MOdulate and DEModulate give the modem its name. Modem communications involve three elements of personal computing: serial ports, modem commands, and communications software.

Classification based on purposes:

There are either special-purpose or general-purpose computers. A special-purpose computer is designed for a specific application. It is also known as dedicated computer. Many such computers have instructions permanently programmed into them that are designed to perform only one major function. Special-purpose computers are used to control traffic lights, to control the collection of tolls on highways, and in automobiles, weapons, appliances and games etc.

General-purpose computers are used to handle a variety of tasks. This is possible by the stored-program concept. By this concept, a program containing a series of instructions is prepared for an application and temporally stored in memory. Once stored in the computer’s memory, the program can be executed to perform the specific function. After the completion of the execution of one program, another program can be used for some other task. That is, the same hardware can be used to execute many different programs.

General-purpose computers are more versatile than special-purpose computer. But when applied to the same task it is seen that general-purpose computers are less efficient and also slower than special-purpose computers 

Classification based on signals:

Two types of computers based on internet signaling are analog computers and digital computers. An analog computer actually represents quantities by the physical analogies. These kinds of computer represent the physical quantities, such as distance, acceleration, velocity, temperature, or angular position, pressure, force etc. by electrical or mechanical parameters.

The example of an analog-computing device is automobile speedometer. It changes the rotating rate of the drive shaft of a car into the numerical value of the speed of the automobile. The example of an analog device is a thermometer. It converts the movement of a column of mercury into a temperature reading.

Analog computers are ideal in situations where data can be accepted straightly from measuring instruments. The capability to gather data at high speeds and to process data at uniformly high speeds, makes analog computers exclusively suited to controlling processes of oil refineries, weapon systems steel mills, and similar other procedures. An analog computer does not need any storage space ability. The out from an analog computer is usually in the form of reading on a dial (as in the speedometer of a car) or a graph plotted on paper.

Analog computers were in use before the invention of the digital computers. There are far more digital computers in use today than analog computers. 

Classification based on capacity:

Capacity of a computer refers to the volume of data that a computer system can process. Formerly a computer’s size was a sign of its capacity. With the current state of smallness, dimension of capacity is based on throughput of the computer. Throughput is the quantity of processing that can be performed in a given amount of time. Based on throughput computer systems can be divided into four major categories:

• Microcomputers
• Minicomputers
• Mainframe computes
• Supercomputers

Microcomputers:

Microcomputers are generally known as personal computers-PCs and are microprocessor based small notebook or laptop or desktop systems with changeable capacity. Personal digital assistants (PDAs) are very small portable computers. PDAs are also recognized as the palmtop computers. The brain of a microcomputer is the microprocessor; it is a silicon chip containing essential circuits to execute logic or arithmetic operations and to manage the input/output operations. A microprocessor is an integrated circuit which usually contains millions of transistors squeezed onto a small silicon chip. A microcomputer system is formed by adding input and output facility along with memory to the microprocessor.

At the initial time the microcomputers had very limited processing power and limited choice of input/output devices. But at modern days they have wider processing capabilities and maintain a wide range of input/output devices. Today microcomputers are available with a collection of input/output devices varying from a tape recorder to a voice synthesizer. In addition to general-purpose computations, microcomputers are also used for exceptional purpose applications in automobiles, airplanes, toys, clocks, appliances etc.

Workstations: The High-end microcomputers are also recognized as workstations. They symbolize the bridge between the microcomputers and minicomputers. It is a microcomputer with many of the facilities and abilities of bigger minicomputers but price much less. At first it was designed for use by designers and engineers who need extremely powerful processing and output capabilities.

Servers: Servers are not designed to be used directly. They make programs and data available for users having access to a computer network. A computer network is a collection of computers connected together.

Clients: To use servers, users run desktop programs called clients, which know how to contact the server and obtain information from the server. Use of desktop clients and centralized servers is called client/server computing.

Terminals: Although terminals look like the personal computers, they have some limitations when compared with personal computers. Terminals have only a screen and a keyboard and the electronics that allow them to communicate with the computer to which they are connected. Because they lack the ability to process data on their own, they are called dumb terminals. There is a variety of dumb terminals that can perform limited processing. These are called smart terminals. A personal computer is an example of a smart terminal.

Minicomputers:

A minicomputer system performs the basic arithmetic and logic functions and supports some of the programming language used with large computer systems. They are physically smaller, less expensive, and have small storage capacity compared to mainframes. Minicomputers are ideally suited for processing tasks that do not require access to huge volumes of stored data. As a result of low cost, ease of operation, and versatility, minicomputers have gained repaid acceptance since their introduction in the mid-sixties. Some of the larger and expensive minicomputers are capable of supporting a number of terminals in a time-shared mode. Uses of minicomputers are gradually being diminished with the rapid development of microcomputers.

Mainframe Computers:

A larger computer normally consists of modules accumulated on a chassis and is terms as a mainframe computer. They differ in size, from those a little larger than a minicomputer to supercomputers. These computer systems present extensive benefits over minicomputers or microcomputers. Some of these are: greater storage facility, greater processing speed, a larger assortment of input/output devices, and support for a number of high-speed storage devices, multiprogramming, and time sharing.

Owing to wonderful expense, a mainframe computer system must be operated powerfully. Operating mainframes at the necessary level of effectiveness requires a very large and highly trained staff. These are normally used by government agencies, large business, military and the universities. These systems are often coupled with other computer systems in a large network to give massive computing power. This is referred to as a distributed data processing system. 

Supercomputer:

A very powerful and large mainframe computer is known as a supercomputer. The astronomical cost of super-computers has limited their development to only a few hundred worldwide. The example of a supercomputer is the Cray X-MP. Such supercomputers are applied to the solution of very difficult and complicated scientific and technical problems. Supercomputers are also used for the various national security purposes of some advanced nations.