System Unit & Motherboard

System Unit

The system unit is a box that contains different components of the computer system. It is also called a chassis. It is made of plastic or metal to protect the components inside it. Most storage devices reside inside the system unit. Other devices like keyboard, mouse, speakers, and printers reside outside the system unit.

There are different types of system units. Some system units sit on the top of a desk. A type called tower model stands vertically on the floor. A type called all-in-one computer contains the system unit and the monitor in the same box. In laptop computers, keyboard and pointing devices are built on the top of the system unit.


The motherboard is also called system board. It is the most important circuit board in system unit. It contains different chips. A chip is a small semiconductor that contains integrated circuits on it. Integrated circuit (IC) is a microscopic path that carries electrical current. An IC may contain millions of transistors. A transistor works as an electronic gate that opens or closes the circuit for electronic signals.

Chips are attached to a circuit board like motherboard, memory module or card. There are different types of chip packages that are as follows:

  • DIP: DIP stands for the dual-line package. It consists of two parallel rows and downward-pointing thin metal pins. The pins attach chip package to the circuit board.
  • PGA: PGA stands for pin grid array. It holds a larger number of pins as the pins are mounted on the surface of the package.
  • FC-PGA: FC-PGA stands for flip chip-PGA. It is a higher performance PGA. It laces the chip on the opposite side of the pins.
  • SEC: SEC stands for single edge contact. It connects to the motherboard on one of its edges.

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