Monday, April 12, 2010



A computer system is a group of machines, or hardware that accepts data, process it, and display information. The main reason for using computer system is to process data quickly and efficiently so that the information obtained is timely, meaningful, and accurate.

A computer system performs its information processing operations under the control of sets of instructions called programs. Computers read incoming data called input, process the data, and display outgoing information called output.

Data itself consists of raw facts, data that is processed or operated to produces structured, meaningful information. Information processing is a set of procedures used to operate on data and produce meaningful results.

Computer system consists of the following components; input devices, main memory and the central processing unit, output devices, and secondary storage devices.

There are many different types of input devices; keyboards, disk drives, page scanner, optical reader, and voice recognition units, to name a few. Each input device reads a specific form of data; for example, keyboard transmits typed characters whereas scanners “read” typed or handwritten characters from documents or images from graphs, photos, or drawings. Any input device converts data into electronic pulses that are transmitted to the CPU for processing.


Main memory stores programs and data for processing and the Central Processing Unit, or CPU, controls all computer operations. The CPU reads data into main memory from an input device, processes the data according to program instructions, and produces information by activating an output device.

The CPU is the “brains” of the computer system. The unit that houses main memory and the CPU must be linked by cables (or by communication channels such as telephone lines) to all input and output devices in the computer system.

The program, or set of instructions for processing data, is read into main memory by the CPU before data can be entered and processed and information generated.

Each output device in a computer system accepts information from main memory under the control of the CPU, and converts it to an appropriate output form.

A printer, for example, is an output device that prints reports or graphics based on information that the CPU has processed and produced. Similarly, a video monitor is an output device that displays both text and graphics on a screen.

Once you turn off a computer, the data and instructions operated on by the CPU are lost. For this reason, separate storage devices are needed to keep the data and instructions in electronic form for then to be conveniently used again and again. Disks are common storage media for PCs and for larger computer systems.

A computer has two types of storage, namely main memory or PRIMARY STORAGE and external storage or called SECONDARY STORAGE. Main Memory contains computer program and the data currently being processed. It is volatile (i.e. it loses its contents when power supply is switched off). Secondary Storage stores data and programs that are not currently required by the CPU. It is transferred to the Main Memory when required. It is non-volatile (i.e. it retains data even though power supply is switched off)


Before computer hardware can actually read data, process it, and produce information, it needs a set of instructions – a program – that actually controls the CPU operations. Programs, like data, are read into main memory under the control of the CPU.

We say that computers are stored-program-devices because they require a set of instructions to be stored in the computers main memory before data can be processed.

Computer professionals called programmers write programs for each user need or application area. The total set of programs that enables the computer system to process data is referred to as software.

Computers require two types of software; System Software to monitor and supervise the overall operations of the computer system and Application Software to manipulate input data and provide users with meaningful output information.


Computers use a series of control programs, called the operating systems, that moves data in and out of main memory and monitors the running of application programs.
The operating system is the primary component of system software. Some computers have built-in operating system, but these cannot be easily changed or updated.

Most computer manufacturers either provide their own operating system, usually on disk, or allow users to purchase disks containing the more popular operating systems.

Operating systems interact with users by means of a user interface. Some operating systems, especially those for larger computer systems, are text based and require the user to learn a set of commands (command line interface)

Some operating systems for PCs like the Macintosh operating systems, permit users to select commands from graphic symbols, or icons, displayed on the screen. Text-based operating systems, like DOS (Disk Operating System) for IBM and IBM compatibles computers, can work in conjunction with graphical user interfaces like windows, which make them easier to use or more user friendly.

Application programs are designed to satisfy user needs by operating on input data to perform a given job, for example, to prepare a report, update a master payroll file, or print customer bills.

Typically, application programs are acquired in one of two ways; Package programs purchased off-the-shelf from a software retailer or; Custom programs designed especially for the unique needs of an individual or an organization

Packaged programs allow limited customization, but they really are intended to be used as is by a broad range of users. Although they may not meet all aspects of every users need, application packages are inexpensive compared to custom programs and are supplied with comprehensive user reference manuals called documentation.

Custom software, on the other hand, is written by programmers within an organization, by outside consultants, or by self-employed programmers. Custom programs are designed to meet the precise needs of users, but they are very time consuming and costly to develop.

Since the 1940’s, four generations of computers have evolved. From the first to the fourth, the trend has been to produce more powerful, less expensive, smaller and more reliable computer systems.

First generation

The first commercial electronic computer was UNIVAC 1 (Universal Automatic Computer). This machine was developed specifically for scientific and military purposes, but was dedicated to business data processing applications.

The characteristic that distinguished first generation computers from subsequent machines was the use of vacuum tubes to control internal operations. Vacuum tube un-reliable, generate a lot of heat, required air-conditioning system.

Binary notation was used instead of decimal notation. All instructions and information were stored in the computer as 1s and 0s, which corresponds to the electronic conditions ‘on’ and ‘off’.


They took several minutes to ‘warm up”. When they were completely warmed up, they became quite hot. Early computers used thousands of vacuum tubes. They occupied the whole rooms and required an enormous amount of electric current to keep them going.

Second generation

In the late 1950s, tiny, solid-state transistors replaced vacuum tubes in computers. The elimination of vacuum tubes greatly reduces generated heat and made possible the reduction in the size of the developed computers.

This generation of computer also uses magnetic cores for representing data in computer. Because cores were far smaller than vacuum tubes, internal storage capacity becomes greater even though the actual size of second generation computers was sharply reduced.

As about the same time, in the early 1960’s, magnetic tape and disks began to be widely used by auxiliary storage. As a result of these developments, a significant increase in the speed and processing capability of computers was achieved.

Third generation

Further technological advancement in electronics brought further reductions in size, greater reliability and speed and lower costs computer. Integrated circuits (ICs) replace the transistors and this marked the development of third generation computers.

This development is known as large-scale integration, or LSI, and is refer to the ability to compress large numbers of Integrated circuits, or transistors, on a single silicon chip. For example, 5,000 transistors can be placed on a chip to produce a digital watch.

Fourth generation

Fourth generation computers continue to be characterized by chips that can contain increasing numbers of items. Now, over 1 million items can be stored on a single chip. This further miniaturization of components, commonly referred to as Ultra-large-scale integration (ULSI), result in increased speed, greater reliability, and enormous storage capacities for current computers.

The Intel Corporation was the first company that developed the microprocessor, or computer on the chip. One chip could contain all the circuits necessary to perform the basic functions of an entire computer. Microprocessors are not only used in fourth generation computers, but for wide variety of products including automobiles, sewing machines, microwave ovens, electronics games and so on.

The microprocessor was a general purpose computer that could be programmed to do any number of tasks, from running a watch to guiding a missile. No longer was it necessary to design circuit specially for each intended purpose. Manufacturers could now make a single type of microprocessor and sell it to other manufacturers, who would use them for thousands of different applications.

The Fifth generation computers

Unlike all other generation computers, this generation of computers is close at hand and is characterized by the use of the technique used to reduce complex programming. This technique used is known as Artificial Intelligence (AI). The Japanese, who are currently at the forefront in the development of fifth-generation computers, refer to them as truly “intelligent machine”.

Classification of Computers

Computers can be loosely categorized according to their capacity for processing data. Large computers called mainframes are used by such customers as banks, air¬lines, and large manufacturers to process very large amounts of data quickly.

The most powerful and expensive computers are called supercomputers. Mini¬computers, which are widely used by colleges and retail businesses, have become increasingly similar to main--frames in terms of capacity. The largest and most ex¬pensive minicomputers are called super minis.

The smallest computers-such as desktop office computers or-home computer are called personal computers, or sometimes microcomputers. Super micros, or work-stations, combine the compactness of a desktop com¬puter with power that almost equals that of a main¬frame. As computer technology-changes, distinctions between types of computers will also change.

A centralized computer system does all processing in one location. In a decentralized system, -the computer itself and some storage devices are in one place, but the devices to access the computer are somewhere else. Such a system requires data communications - the ex¬change of data over communications facilities.

In a dis¬tributed data -processing system, a local office usually uses its own small computer for processing local data but is connected to a central headquarters computer for other purposes.

Often organizations use a network of personal com¬puters, which allows users to operate independently or in cooperation with other computers-exchanging data and sharing resources. Such a setup, often called a local area network (LAN), can even connect personal com¬puters to a mainframe computer to form a micro-to mainframe link, in which users can obtain data from the mainframe and analyze it on their own personal computers.

People and Computers

People are vital to any computer system. An organiza¬tion's computer resources department-often called Management Information Services (MIS) or Com¬puter Information Systems (CIS), Computing 5cr-vices, or Information Service-includes data entry operators (who prepare data for processing), computer operators (who monitor and run the equipment-li¬brarians who catalog disks and tapes), computer programmers (who design, write, test, and implement pro grams), systems analysts (who plan and design entire systems of programs), and a chief information officer (who coordinates the MIS department).

In general, a distinction is made between computer pro¬fessionals, who provide computer systems, and users, who use the systems. However, in a development called the end-user revolution, users have become increas¬ingly knowledgeable about computers and less reliant on computer professionals

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