What's a Computer Bus?
A computer bus is a series of fine wires that allow the connection of interface cards such as graphic, sound and modem cards to be attached to your computer internally. The cards "slot in" and a PC usually has 6 slots - 4 PCI slots and 2 ISA.
The PCI slots are more modern and faster than their older ISA cousins. PCI slots are 32 bit whilst ISA are 8 or 16 bit slots. The more bits there are the faster the card can send and receive data. The bits are the number of wires leading into and out of the card. Each wire is a bit - that is it is capable of carrying 1 bit of information at any one time.
The bus forms a loop that allows the transmission of data to and from the cards to the CPU and other devices (such as memory). Each device is capable of sending and receiving data on the bus. To ensure that each device doesn't receive another card's data (such as your graphics card trying to "display" a sound meant for your sound card), the data is accompanied by an Interrupt Request (IRQ). This is a unique number assigned to each device. Having two or more devices using the same IRQ will result in your system malfunctioning.
Using slower ISA cards rather than faster PCI cards causes bottlenecks here. The downside to using PCI cards is that they do tend to be more expensive, but remember, you can cripple a fast machine by using slow cards, especially for data intensive devices such as a graphics card.
You may come across a device - such as a graphics card - that has a "local bus." This means that rather than transmitting data to and from the CPU, these devices will take the burden of common routines away from the CPU and deal with it themselves. Graphics cards do this with drawing primitives (simple shapes that are often drawn on screen such as squares rectangles and circles). A local bus will help speed up your machine.
For those of you reading this who build their own PC's, make sure you don't cripple a machine by using old, slow devices that can't carry the amount of data needed by modern applications. I have known people ask why their PC is so slow when they built in a new 233 MHz Pentium II only to find that they have used an old, 8 bit 512kb graphics card. It simply can't cope with it! Get a 4MB PCI graphics card and you will notice a major increase in speed!
