The functions of elements of a computer are as follows:
A) Input device:
Data and instructions are interred into computer through input device. The commonly used input device is keyboard. Several input devices which do not need to typing of information have been developed i.e. joystick, light pen, mouse, trackballs, etc. and these are called pointing device.
B) CPU (Central Processing Unit):
It is brain of computer. Its primary function is to execute programs. Besides executing programs, the CPU control the operation of all other components and data are stored in the memory and displayed on the CRT screen or printed on printer. The CPU of small computer is microprocessor. The CPU of large computers has a number of microprocessor.
a. ALU (Arithmetic and Logical Unit):
The function of ALU is to do arithmetic and logic operations such as addition, subtraction, multiplication and division; AND, OR, NOT and Exclusive OR operations. Other mathematical operations such as exponential, logarithmic, trigonometric and floating point operations are not performed by ALU. So these operations are performed by special purpose FPU math processor and modern microprocessor contains FPU (Floating Point Unit) on microprocessor chip itself.
b. CU (Control Unit):
The CU controls the entire operation of computer. It also controls all other devices such as memory input and output devices connected to the CPU. It maintains order and directs operation of the entire system. It fetches instruction from the memory, decodes the instruction, interprets the instruction to know what tasks are performed and sends suitable control signals to other components to perform further necessary steps to execute instruction.
c. Register:
Register is a temporary storage locations in the CPU that are designed for storing data temporarily during program execution. Register quickly accept, store and transfer data and instruction that are used immediately. The number of registers differs from processor to processor.
C) Memory:
Memory is an essential component of a digital computer. It is storing device. It stores programs, data, results etc.
i) Primary Memory:
The main or primary memory is a fast memory which stores programs along with data that are required to execute user's program. The main memory is directly addressed by CPU. A computer contains two types of memory a) RAM and b) ROM
a) RAM (Random Access Memory):
RAM is an R/W memory of computer. The users can write information into RAM and read information from it. Ram is volatile memory because the information written into it is retained in it as long as power supply is on. As the power supply goes off its stored information is lost. It is accessible to users. RAMs are expensive in comparison to ROM. Types:
1 - SRAM (Static RAM):
SRAM retain stored information only as long as power supply is on. SRAM is costlier and consume power. They have higher speed, i.e. 10-100 ns and do not need refreshing circuit, it requires large space.
2 - DRAM (Dynamic RAM):
DRAM loses its information in a very short time even though power supply is on. It requires less space; in a DRAM binary state is stored for refreshing the circuit in every 2 milliseconds to leakage away the data. They consume less power. They are used where large capacity of memory is needed. DRAM is cheaper and has high packing density. The refreshing and control circuitry for a DRAM may be either itself or on separate IC controller. They have lower speed, i.e. 40-70 ns.
b) ROM (Read Only Memory):
It is a non-volatile memory i.e. the information stored in it is not lost even if power supply goes off. It is used for permanent storage of information. Information can't be written into ROM by users / programmers. The contents are permanently stored in a ROM at the time of manufacture. ROM are cheaper in comparison to RAMs.
1 - PROM:
It is programmable read only memory. The contents are decided by the user. The user can store permanent programs, data or any other kinds of information in a PROM. PROM are once programmable. PROM are cost effective if small number of chips is to be produced to store certain fixed program with the help of PROM programmer the user stores his programs in a PROM.
2 - EPROM:
EPROM is an erasable PROM. The stored data in EPROM can be erased by exposing it to high intensity short wav ultraviolet light for about 20 minutes. These types of memory are used in product development and experimental projects.
3 - EEPROM:
EEPROM is an electricity erasable PROM. The chip can be erased and reprogrammed on board easily on a byte by byte basis. Either a single byte or the entire chip can be erased in one operation. It requires much shorter time, a few milliseconds. It also has limited life span i.e. the number of times it can be re-programmed is limited to tens or hundreds or thousands of times.
ii) Secondary memory:
The secondary memory is employed for mass storage of data, programs and other information's. It has much larger capacity than main memory. Secondary memory is also known as auxiliary memory. The information which is not being currently processed resides in secondary memory. The information needed by CPU for current processing is transferred form secondary memory to main memory. Hard disk and floppy disk are used for secondary memory.
Output Device:
Output is the action of getting information from computer. The computer sends information to an output device in binary form. An output device convert it in to a suitable from convenient to users such as printed form, display on screen, voice output etc.
Output can exist in two forms:
1) Hard copy output:
Hard copy refers to recording letters, graphics or picture on permanent medium such as paper or film. Examples: printers, plotters.
b) Soft copy output:
Soft copy output refers to the output on temporary form i.e. displayed on the screen e.g. monitor, voice output etc.
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