Motherboards and Buses - Upgrading and Repairing PCs - page 230

For performance information about the performance of older bus types such as ISA, EISA, VL-BUS,
and MCA, see Table 4.71 in Chapter 4, “Motherboards and Buses,” in Upgrading and Repairing
PCs, 19 th Edition, available in its entirety on the DVD packaged with this topic.
Note that many of the buses use multiple data cycles (transfers) per clock cycle to achieve greater
performance. Therefore, the data transfer rate is higher than it would seem for a given clock rate,
which allows for an easy way to take an existing bus and make it go faster in a backward-compatible
way.
The Processor Bus (FSB)
The processor bus (also called the FSB) is the communication pathway between the CPU and
motherboard chipset—more specifically the North Bridge or Memory Controller Hub. Over time, the
FSB has run at faster speeds to support faster processor, memory, and motherboard speeds. But as the
previous table indicates, there are many other buses running at different speeds in typical systems.
The Socket 7 architecture used by Intel's Pentium processors in the mid-1990s, the Socket 478
architecture used by Intel processors in the early 21 st century, and the Socket 939 architecture used by
AMD processors in the middle of the last decade represent significant milestones in processor bus
designs. Socket 939's pioneering use of an integrated memory controller in the processor is now
followed by both AMD and Intel processors.
For an in-depth comparison of the processor and other buses found in systems on Socket 7 (Intel and
AMD), Socket 478 (Intel), and Socket 939 (AMD) processors, see “The Processor Bus (Front Side
Bus)” in Chapter 4, “Motherboards and Buses,” in Upgrading and Repairing PCs, 19 th Edition,
available in its entirety on the DVD packaged with this topic.
Types of I/O Buses
Since the introduction of the first PC, many I/O buses have surfaced. The reason is simple: Faster I/O
speeds are necessary for better system performance. This need for higher performance involves three
main areas:
• Faster CPUs