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Computer System


Block diagram of a Computer System

Input & Output Device:

Input Device: The device through which a computer takes input is called as Input Device.


Mouse, Keyboard, Scanner, Joy stick, Driving Wheel, Screen touch monitor, light pen, Microphone etc.

Output Device: The device through which a computer gives only information to its user is called output device.


Monitor, Speaker, Printer and Plotter etc.

CPU (Central Processing Unit):

CPU is the main processing unit of a digital computer. The data taken by input device is processed here and turned into information.

There are three main components in CPU;

  • ALU (Arithmetic logic unit).
  • CU (Control unit).
  • Register.

ALU (Arithmetic logic unit): ALU is the main block which does all types of arithmetic operation. Some logical operation is also done by ALU.

CU (Control unit): Control unit is the main control portion of a computer. It controls which task or work will be done at first.

Register: Register is one type of memory which is situated within CPU.


Memory is the main portion where all kinds of data are stored. CPU takes data from memory when it wants.


Classification of Computer Memory


Primary Memory Primary memory stored information for a certain period. When the power goes off all the information erased from the memory.

RAM (Random Access Memory): The information stored in RAM depends on the electric power. When the power goes off all the information get removed from RAM. RAM is also called as volatile memory.

  • S-RAM (Static RAM): S-RAM is fast and expensive. Storage space is low.
  • D-RAM (Dynamic RAM): D-RAM is slower and cheaper than S-RAM. D-RAM has high storage space.

ROM (Read only Memory): All the things are stored into ROM using logic gate. ROM is non-volatile type. So, if the power goes off all the things will be still stored in ROM. Different types are ROM are there;

  • E. ROM(Erasable ROM)
  • P. ROM(Programmable ROM)
  • E.P ROM(Erasable Programmable ROM)
  • E.E.P ROM(Electronically Erasable Programmable ROM)

Cache Memory Cache Memory is very high speed storage unit. It is placed between CPU and Main Memory. It works as a buffer in high speed computer. Cache Memory is costlier than main memory. There are three types of cache memory;

  • Asynchronous SRAM.
  • Synchronous Burst SRAM.
  • Pipeline Burst SRAM.

Secondary Memory To store huge amount of information secondary memory is needed.


Magnetic Media, Floppy Disk, Hard Disk, Compact Disk.