Understanding Expansion Buses

Understanding Expansion Buses

Expansion cards are integrated circuit card that plug into an expansion slots on a motherboard to provide access to additional peripherals or features (such as video, sound, image capture cards, etc.) not built into the board. Also referred to as an add-in-board Expansion slot is a slot on the motherboard that physically and electrically connects an expansion card to the motherboard and the system buses.

CPU speeds increased as technology improved, while the speeds of expansion cards remained relatively constant. It was not practical to redesign and replace every expansion card each time a new processor was released—this would have been complicated and expensive for manufacturers..

To resolve this problem, designers have divided the external data bus into two parts:

System bus: 

This supports the CPU, RAM, and other motherboard components. The system bus runs at speeds that support the CPU.

Expansion bus:

 A bus/slot on the motherboard that physically and electrically connects for expansion card to the motherboard and system buses. Expansion bus also called I/O buses. 

The main difference among buses consists primarily of their architecture the amount of the data they can transfer at a time and speed at which they can do it. Following section describes the different types of the PC buses.