Windows 2000 Performance Guide

I/O Buses

In this section, we talk about I/O buses and discuss the advantages and disadvantages of each of the available options. The I/O bus sits between the I/O devices, such as your disk, modem, and video card, and the system/memory bus. On your motherboard, the I/O bus makes itself visible through the expansion cards available on it, although your motherboard may have one or more I/O buses supporting the expansion cards that you see. The first standard I/O bus available in the PC industry was the ISA (Industry Standard Architecture) bus. For many years before that, cards were developed based on a loosely defined standard. As time went on, more and more problems surfaced as the bus clock speed kept being pushed further, so eventually the industry decided to firmly define the characteristics of the AT I/O bus interface. The result of this standardization effort was the ISA bus, which runs at 8.25 MHz and has a throughput of 1.5 Mbps to 5.0 Mbps. Given today’s demanding applications and high-speed devices, this bus is considered too slow and is not present in high-end systems. On motherboards where it is available for backward compatibility, make sure that you use it only for slower devices where performance is not critical. For example, serial ports, modems, and sound cards can be supported at full capacity by an ISA bus slot. On the other hand, high-speed devices such as SCSI adapters and network adapters must be on a faster bus interface, such as a PCI bus. Even though the ...