System Bus and Expansion Cards

You’re furious! You just bought an expensive digital camcorder only to find out that it can’t connect to your computer because your computer apparently doesn’t have a Firewire port. Don’t worry—you can easily add a Firewire port to the computer by buying an expansion card.

Expansion cards allow you to add more gizmos and capabilities to a computer. You can also use expansion cards to replace a component of a computer that breaks, like a modem. Expansion cards plug into expansion slots on a computer’s motherboard.

A computer talks to its expansion cards—and everything else on the motherboard—through its bus. A computer’s bus is an electronic pathway that carries information between devices in a computer. Two factors determine how information flows through the bus: the bus width and the bus speed.

· Bus Width

The bus width determines how many ―lanes‖ there are on a computer’s electronic highway. Actually, the bus width isn’t measured in lanes, but in bits. The wider the bus, the more information can travel across it at the same time.

· Bus Speed

The bus speed determines how fast information can travel through the bus. The higher the bus speed, the faster information can travel through it. Bus speed is measured in MHz.

As if this weren’t confusing enough there are several bus types out there. They include:

· ISA

The Industry Standard Architecture (ISA) is the original, slowest, and oldest type of bus. The ISA bus has a width of 16 bits and a speed of 8 MHz. The ISA bus is going the way of dinosaurs and is no longer found on new computers.

· PCI

The Peripheral Component Interconnect (PCI) bus is the main bus found in computers. The PCI bus can have a width of 32 or 64 bits. The PCI bus supports Plug and Play, which lets you add new devices to a computer without a complicated installation process. PCI Express is the next generation of PCI. PCI Express uses PIC programming concepts and communications standards but is based on a much faster serial communications system.

· AGP

An Accelerated Graphics Port (AGP) is a blazingly fast bus that is currently only used for video cards. The AGP port has a width of 64 bits and supports Plug and Play. So what kind of expansion cards are out there? Here are some of the more common expansion cards that you may come across…