Structure of Desktop computers

Computer consists of a set of hardwares and softwares.

Desktop Computer

A computer system can be viewed as a  combination of input, processing and output  subsystems.
Input –> Process –> Output
Hardware examples:

  • Keyboard
  • Monitor
  • Mouse, etc.

Software examples:

  • Operating system
  • Computer games
  • Antivirus, etc.


The computer case comtains most of the computer components. 

Power supply

A power supply unit converts alternating current (AC) electric power to low-voltage DC power for the internal components of the computer.


The motherboard is a large rectangular board with integrated circuitry that connects the other parts of the computer including the CPU, RAM, disk drive as well as any peripherals connected via the ports or the expansion slots.

CPU (Central Processing Unit) 

CPU performs most of the calculations which enable a computer to function, and is sometimes referred to as the “brain” of the computer. 


CPU is cooled by a heat sink and fan.


The Chipset, which includes the north bridge, mediates communication between the CPU and the other components of the system, including main memory.

RAM (Random Access Memory)

RAM stores the code and data that are being actively accessed by the CPU.

ROM (Read Only Memory)

ROM stores the BIOS that runs when the computer is powered on or otherwise begins execution, a process known as Bootstrapping, or “booting” or “booting up”. 

BIOS (Basic Input Output System)

BIOS includes boot firmware and power management firmware.


Buses connect the CPU to various internal components and to expand cards for graphics and sound.

CMOS battery

CMOS battery is also attached to the motherboard. This battery powers the memory for date and time in the BIOS chip.

Expansion cards

Expansions cards can be used to obtain or expand on features not offered by the motherboard.

Storage devices

Storage devices, refers to computer components and recording media that save digital data.

  • Fixed storage device : Reside permanently on computers, like hard disk.
  • Removable storage device : USed to transfer data between computers, like USB flash drive.

Input device

Device which provide inputs to the computer. Input device includes keyboard, mouse, scanner, etc.

Output device

The device which display outputs of the computer. Output device includes printers, speakers, monitors, etc.

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