The internal architectural design of computers differs from one model to another. However, the basic components of a computer remain the same for all models. A complete computer installation including the central processing unit, the peripherals such as hard disk drives, floppy disk drives, monitor, printer, mouse and operating system which are designed to work and interact with each other and with the user is called a computer system. A computer system has the following main physical components:

• Input/output Unit

• Central Processing Unit (CPU)

• Memory Unit

Besides the above main components, a computer system has other components such a motherboard, power supply, storage devices, ports, and cards. All the devices of computer except motherboard and CPU are called peripheral devices.

Hardware and Software

Computer components can be broadly divided into two categories – hardware and software. Hardware refers to any physical component of a computer, such as, CPU, monitor, keyboard, hard disk, floppy disk, etc. Software refers to the programs, which are required to operate the computer, for example, DOS (Disk Operating System), Windows, BASIC, COBOL, Oracle, Tally etc. An analogy of hardware can be the book which you are reading while software the text written on this book. Both hardware and software are dependent on each other. CPU, memory unit, hard disk, etc. are useless unless they are provided with instructions and data for storage and processing.

(1) Input/Output Unit

We know that the computer is a machine that processes the input data according to a given set of instructions and gives the output. Before a computer does a processing it must be given data and instruction. After processing, the output must be displayed are printed by the computer. The unit used for getting the data and instructions into the computer and displaying ore printing output is known as Input/output unit.

The input unit is to enter data and instruction into a computer. There are many peripheral devices, which are used as input output units for the computer. The most common form of input devices in known as terminal. A terminal has an electronic typewriter-like device called keyboard along with a display screen, called visual display unit (VDU) or monitor. Keyboard is the main input device while the monitor is an output device. There are some other common input devices like mouse, Punch card, tape, joystick, scanner, modem etc.  Printer and plotter are the other peripheral device says used as output units for the computer.

(2) Central Processing Unit

CPU is the main component or ‘brain’ of a computer, which performs on the processing of input data. Its function is to fetch, examine and then execute the instructions stored in the main memory of a computer. In microcomputers, the CPU is built on a single chip or integrated circuit (IC) and is called a microprocessor. The CPU consists of the following distinct part:

Arithmetic and Logic Unit: The arithmetic and logic unit of CPU is responsible for all arithmetic operations like addition, subtraction, multiplication and division as well as logical operation such as less than, equal to and greater than. Actually, all calculations and comparisons are performed in the arithmetic logic unit.

Control Unit: The control unit is responsible for controlling the transfer of data and instructions among other units of a computer. It is considered as the central nervous system of computer, as it manages and coordinates all the units of computer. It obtains the instructions from the memory, interprets them and directs the operation of the computer. It also perform the physical data transfer between memory and the peripheral device.

Resistors: Registers are small high speed circuits (memory location) which are used to store data, instruction and memory addresses (memory location numbers), when ALU performs arithmetic and logical operations. Registers can store one word of data until it is overwritten by another word. Depending on the processor’s capability, the number and type of registers vary from one CPU to another. Registers can be divided into six categories namely, General purpose registers, Pointer registers, Segment registers index registers flats registers and instruction pointer register depending upon their functions.

Buses: data is stored as a unit of 8 bits (BIT stands for binary digit that is 0 or 1) in a register. Each bit is transferred from one register to another by means of a separate wire. This group of 8 wires, which is used as a common way to transfer data between registers is known as a bus. In general terms bus is a connection between two components to transmit signal between them. Bus can be of three major types, data bus control bus and address bus. The database is used to move data, address bus to move address or memory location and control bus to send control signals between various components of a computer.

Clock: Clock is another important component of CPU, which measures and allocates a fixed time slots for processing each and every micro operation (smallest functional operation). In simple terms, CPU is allocated one or more clock cycles to complete a micro operation. CPU executes the instructions in synchronization with clock pulse.

The clock speed of CPU is measured in terms of megahertz (MHz) or millions of cycles per second and gigahertz (GHz) are billions of cycles per second. The clock speed of CPU varies from one module to another in the range 4.77 MHz (in 8088 processor) to several GHz (in latest pentium processors). CPU speed is also specified in terms of millions of instructions per second (MIPS) or million of floating point operation per second (MFLOPS).

(3) Memory Unit

Memory unit is the component of a computer system, which is used to store data, instructions and information before, during and after the processing by ALU. It is actually a work area (physically a collection of integrated circuits) within the computer, where the CPU stores the data and instructions. It is also known as main/primary/internal memory. Memory unit of computer is of the following seven types

Read only memory: ROM is an essential component of the memory unit. We know that the computer, being a machine, itself has no intelligence or memory and requires instructions, which are given by man. Whenever the computer is switched on it searches for the required instructions. This memory is permanent and it is not erased when the system is switched off. So ROM is a non-volatile memory. As appears with its name, it is read type of memory that is it can be read only and not be written by user or programmer.

ROM contains a number of programs or set of instructions. The most important program of ROM is the basic input output system (BIOS) which activates the hardware (physical components of computer) such as keyboard, monitor, floppy disk etc., in communicating with the system and application software (set of instruction or program).

Random Access Memory: RAM is another important component of the memory unit. It is used to store data and instructions during execution of programs. Contrary to ROM, RAM is a temporary and is erased when the computer is switched off. So, RAM is a volatile memory. RAM is a read/write type of memory, and thus can be read and written by the user or programmer. As it is possible to randomly use any location of this memory, this memory is known as random access memory.

Complementary metal oxide semiconductor memory (CMOS): CMOS memory is used to store the system configuration, that, time and other important data. When the computer is switched on, BIOS matches the information of CMOS with the peripheral devices and displays error in case of mismatching.

Flash memory: Flash memory is a memory chip that holds its content without power. It is derived from the EEPROM chip technology. Flash memory is so called as it can be erased ‘in a flash’. Unlike RAM chips, in which a single byte can be written flash memory must be erased and written in fixed blocks ranging from 512 bytes to 256K. Flash memory is cheaper and more devise. It is used to replace RDM BIOS chips so that BIOS can be updated.

Cache memory: Cache memory is a temporary storage area where the most recently called data and instructions from RAM are stored by the processor. When a processor needs and instruction from RAM, it first looks for that instruction in cache memory. Cache memory speeds up processing. Some personal computer have cache memory chips hardwired on to the motherboard. Operating systems are typically capable of setting aside a portion of RAM to be used as cache memory and the size of the cash can be set by the user. In addition, many expansion cards contain cash for specific purpose, such as for storing digitized sound or video.

Virtual memory: Virtual memory is a portion of the external memory, generally a hard disk used as an extension of its immediate access memory. Typically, hard disk drives (HDD) are used to store programs and data files. Another way to use a HDD is to designate a portion of it to be used as virtual memory. When using virtual memory, a computer treats parts of a HDD connected to it as additional RAM. If the user has the necessary free HDD space, using virtual memory will enable him or her to work with large programs and other files without installing additional RAM.

RAM Disk: in RAM Disk you can also store various types of information, including lookup tables from a database itself by creating a dummy hard disk within the RAM itself. This disk is accessible just like any other hard disk, except that it contents are completely wiped off when the machine power is reset. Thus, a RAM disk is used for lookup tables or non-critical data which is not a frequently updated and requires instant access.

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