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TEXT 9. WHAT IS A COMPUTER?

Computers are electronic machines which can accept data in a certain form, process the data and give the results of the processing in a specified format as information.

Three basic steps are involved in the process. First, data is fed into the computer's memory. Then,when the program is run, the computer performs a set of instructions and processes the data. Finally,we can see the results (the output) on the screen or in printed form.

Information in the form of data and programs is known as software, and the electronic and mechanical parts that make up a computer is system are called hardware. A standard computer system consists of three main sections: the central processing unit (CPU), the main memory and the peripherals.

Perhaps the most influential component is the central processing unit. Its function is to execute program instructions and coordinate the activities of all the other units. In a way, it is the ‘brain’ of the computer. The main memory holds the instructions and data which are currently being processed by the CPU. The peripherals are the physical units attached to the computer. They include storage devices and input/output devices.

Storage devices (floppy, hard or optical disks) provide a permanent storage of both data and programs. Disk drives are used to handle one or more floppy disks. Input devices enable data to go into the computer’s memory. The most common input devices are the mouse and the keyboard. Output devices enable us to extract the finished product from the system. For example, the computer shows the output on the monitor or prints the results onto paper by means of a printer.

On the rear panel of the computer there are several ports into which we can plug a wide range of peripherals — modems, fax machines, optical drives and scanners. These are the main physical units of a computer system, generally known as the configuration.

The nerve centre of a microcomputer is the central processing unit or CPU. This unit is built into a single microprocessor chip - an integrated circuit - which executes program instructions and supervises the computer’s overall operation. The unit consists of three main parts:

· the control unit, which examines the instructions in the user’s program, interprets each instruction and causes the circuits and the rest of the components - disk drives, monitor, etc. - to be activated to execute the functions specified;

· the arithmetic logic unit (ALU),which performs mathematical calculations (+, -, etc.) and logical operations (and, or, etc.);

· the registers, which are high-speed units of memory used to store and control information. One ofthese registers is the program counter (PC) which keeps track of the next instruction to be performed in the main memory. Another is the instruction register (IR) which holds the instruction that is currently being executed.

One area where microprocessors differ is in the amount of data - the number of bits - they can work with at a time. There are 8, 16, 32 and 64-bit processors. The computer’s internal architecture is evolving so quickly that the new 64-bit processors are able to address 4 billion times more information than a 32-bit system.

The programs and data which pass through the central processor must be loaded into the main memory (also called the internal memory) in order to be processed. Thus, when the user runs an application, the microprocessor looks for it on secondary storage devices (disks) and transfers a copy of the application into the RAM area. RAM (random access memory) is temporary, i.e. its information is lost when the computer is turned off. However, the ROM section (read only memory) is permanent and contains instructions needed by the processor.

Most of today’s computers have internal expansion slots that allow users to install adapters or expansion boards. Popular adapters include high-resolution graphics boards, memory expansion boards, and internal modems.

The power and performance of a computer is partly determined by the speed of its microprocessor. A clock provides pulses at fixed intervals to measure and synchronize circuits and units. The clock speed is measured in MHz (megahertz) and refers to the frequency at which pulses are emitted. For example, a CPU running at 500 MHz (500 million cycles per second) is likely to provide a very fast processing rate and will enable the computer to handle the most demanding applications.