General Knowledge

Components of system unit

  • These are some of the major components present inside the  system unit. They are:

A Computer Base Unit



  • The motherboard is the main component inside the case.
  • It is called main board.
  • It is a large rectangular board with integrated circuitry that connects the rest of the parts of the computer including the CPU, the RAM, the disk drives (CD,DVD, hard disk, or any others) as well as any peripherals connected via theports or the expansion slots.
  • Components directly attached to the motherboard include:
  • The 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.
  • It is usually cooled by a heat sink and fan.
  • The chip set mediates communication between the CPU and the other components of the system, including main memory.
  • RAM (Random Access Memory) stores all running processes (applications) and the current running OS.
  • The BIOS includes boot firmware and power management.
  • The Basic Input Output System tasks are handled byoperating system drivers.
  • Internal Buses connect the CPU to various internalcomponents and to expansion cards for graphics and sound.
  • CurrentThe north bridge memory controller, for RAM andPCI Express
  •  PCI Express, for expansion cards such as graphicsand physics processors, and high-end networkinterfaces
  • PCI, for other expansion cards
  •  SATA, for disk drives.
  • External Bus Controllers support ports for external peripherals.
  • These ports may be controlled directly by the south bridge I/O controller or based on expansion cards attached to the motherboard through the PCI bus.
  • USB
  • FireWire
  • SATA
  • SCSI


Hard Disk Drive

  • A hard disk drive is a high capacity, non-volatile, magnetic data storage device with a volume (disk) that is usually non-removable.
  • Data is magnetically read and written on the platter by read/write heads that float on a cushion of air above the platters.


Floppy Disk Drive

  • This is a disk drive that can read and write floppy disks, although they are obsolete nowadays.
  • These drives have been replaced by the USB flash disk drives in modern machines.





Power supply

  • A power supply unit (PSU) is the component that supplies power to the other components in a computer.
  • Power supply units often used in computers are SMPS (Switch Mode Power Supply).
  • The SMPS provides +12, -12,+5, -5 and 3.* DC Volts for operation.
  • When using the SMPS, it results in uninterrupted output within a wide range of input AC voltages.
  • SMPS makes the power supply unit compact, rigid and reliable.
  • The power supply unit (PSU) is used to convert AC currents from the main supply to the different DC voltages required by various computer components.
  • Power supplies are quoted as having a certain power output specified in watts, A standard power supply would typically be able to deliver around 350 watts.
  • You will need more power from the power supply if your PC has more operating components.



PORT:A port is a physical docking point using which an external device can be connected to the computer. It can also be programmatic docking point through which information flows from a program to the computer or over the Internet.

  • Characteristics of Ports

A port has the following characteristics −

  • External devices are connected to a computer using cables and ports.
  • Ports are slots on the motherboard into which a cable of external device is plugged in.
  • Examples of external devices attached via ports are the mouse, keyboard, monitor, microphone, speakers, etc.


  • few important types of ports −

Serial Port

  • Used for external modems and older computer mouse
  • Two versions: 9 pin, 25 pin model
  • Data travels at 115 kilobits per second

Parallel Port

  • Used for scanners and printers
  • Also called printer port
  • 25 pin model
  • IEEE 1284-compliant Centronics port

PS/2 Port

  • Used for old computer keyboard and mouse
  • Also called mouse port
  • Most of the old computers provide two PS/2 port, each for the mouse and keyboard
  • IEEE 1284-compliant Centronics port

Universal Serial Bus (or USB) Port

  • It can connect all kinds of external USB devices such as external hard disk, printer, scanner, mouse, keyboard, etc.
  • It was introduced in 1997.
  • Most of the computers provide two USB ports as minimum.
  • Data travels at 12 megabits per seconds.
  • USB compliant devices can get power from a USB port.

VGA Port

  • Connects monitor to a computer's video card.
  • It has 15 holes.
  • Similar to the serial port connector. However, serial port connector has pins, VGA port has holes.

Power Connector

  • Three-pronged plug.
  • Connects to the computer's power cable that plugs into a power bar or wall socket.

Firewire Port

  • Transfers large amount of data at very fast speed.
  • Connects camcorders and video equipment to the computer.
  • Data travels at 400 to 800 megabits per seconds.
  • Invented by Apple.
  • It has three variants: 4-Pin FireWire 400 connector, 6-Pin FireWire 400 connector, and 9-Pin FireWire 800 connector.

Modem Port

  • Connects a PC's modem to the telephone network.

Ethernet Port

  • Connects to a network and high speed Internet.
  • Connects the network cable to a computer.
  • This port resides on an Ethernet Card.
  • Data travels at 10 megabits to 1000 megabits per seconds depending upon the network bandwidth.

Game Port

  • Connect a joystick to a PC
  • Now replaced by USB

Digital Video Interface, DVI port

  • Connects Flat panel LCD monitor to the computer's high-end video graphic cards.
  • Very popular among video card manufacturers.


  • Sockets connect the microphone and speakers to the sound card of the computer


CD-ROM Drive

This is a high capacity optical data storage device with a removable disk. It writes data onto or reads data from a storage medium.

A CD-ROM drive may be connected to the computer via an IDE (ATA), SCSI, S-ATA, Fire wire, or USB interface or a proprietary interface.

A CD Rom Drive