Computer Peripherals || Introduction to Computer Systems || Bcis Notes



Computer Peripherals

Computer Peripherals is an external device that provides input and output for the computer. For example, a keyboard and mouse are input peripherals, while a monitor and printer are output peripherals.

Machine cycle

The four operations of the CPU compared to a machine cycle. Steps were taken by CPU to run a program (instructions are in machine language)

  • Fetch: obtain program instruction or data item from memory(memory).
  • Decode: Translate instructions into comands (control unit).
  • Execute: carry out the command(ALU).
  • Store: stores to memory(memory).



  • There are three kinds of buses linked between the CPU primary storage and the other devices in the computer system they are:
  1. Data bus: pass information in bi-directional.
  2. Address bus: transmits signals for locating given address in primary storage indicating where data should be placed.
  • Control bus: transmits signals specifying whether to read or write data to or from primary storage address, input device or output device.

The Arithmetic-logic unit and control unit

An ALU and CU are one of the core components of all central processing units.

  • Arithematics logic unit is the part of the CPU that handles all the calculations the CPU may need.
  • It does all processes related to arithmetic and logic operations that need to be done on instruction words.
  • It is also known as an integer unit (IU).

It  performs the following operations:

  1. Logical operations : these include AND,OF,NOT,XOR,NOR,NAND etc.
  2. Bit-shifting operations: shifting the positions of the bits by a certain number of places to the right or left, which is considered as multiplication operation.
  3. Arithematics operations: this refers to bit addition and subtraction.


  • The control unit coordinates and controls the other parts of the computer system.
  • It reads a stored program one instruction at a time and directs other components of the computer system to perform the programs required tasks.

The faster the processor, the more expensive the computer

              Intel processor           Desired clock speed
Itanium or Xeon 1.3 GHZ and UP
Pentium 3.0 GHand UP
Family 2.4 GHZ to 3.0 GHZ UP to 2.4 GHZ
Celeron 2.2 GHZ and UP



Categories of computers and computer systems

Computers are classified into two types:

  • Special-purpose computer
  • General-purpose computer


Special-purpose computer

  • It is a computer designed for a particular function, executing the same stored set of instructions whenever requested. For example microwave, washing machine, medical equipment, etc.


General computer
  1. Microcomputer

  • They are sometimes called PCS, it is one that can be placed on a desktop or carried from room to room.
  • The smallest microcomputers are known as laptop computers or notebook computers.
  • desktop computers are compact microcomputer systems that fit on a desk and are designed to use by individuals.
  • A work station is the largest type of microcomputer applications.
  1. Minicomputers

  • They are more powerful and more expensive than microcomputers.
  • They are smaller and cheaper compared to mainframes.
  • They also can be a server, which is used for managing internal company networks or websites.
  • Server computers are specifically optimized to support a computer network enabling users to share files software peripheral devices (such as printers) or other network resources.


  1. Mainframes computer

  • It is the largest computer, a powerhouse with massive memory and extremely rapid processing power.
  • It is used for very large business, scientific or military applications where a computer must handle massive amounts of data or many complicated processes.


  1. Supper computers

  • It is a highly sophisticated and powerful computer that is used for tasks requiring extremely rapid and complex calculations with hundreds of thousands of variable factors.
  • It is used in many areas of scientific research weather prediction, aircraft design, nuclear weapon and so on.



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