A chipset is designed by the manufacturer to work with a specific set of processors. Most chipsets only support one generation of processors. Why make it complicated like that? Well, the reason is simple. The design of the control circuitry must be different for each processor generation due to the different ways they employ cache, access memory, etc. For example, the Pentium Pro and Pentium II have level 2 cache within the CPU itself, so obviously they would need a different circuitry design than the original Pentium, which has level 2 cache on the motherboard.

Chipsets often support processors using the same core. For example, Athlon XP uses the same processor core as the corresponding Duron processors, so it is quite common to see boards that support both processors. The same situation is true for Celerons and Pentium III’s and Pentium IV’s, depending on the generation we are talking about. In older systems, we found that AMD K6-class processors could often use the same chipsets as the Intel Pentiums. The K6, as well as the Cyrix 6×86, was designed to be compatible with Intel in this way. But, Intel, at the time, had the advantage because they were actually producing chipsets while AMD was not. AMD did finally get into chipsets, although they still are not as big in this market as Intel is. Instead, other chipset manufacturers such as Via and Ali chimed in and took up the slack. Companies like Via produce chipsets today that work quite well with AMD processors among other brands, including Intel. 

Processor Speed Support

Faster processors require chipsets capable of handling them. The specification of the processor speed is done using two parameters: the memory bus speed and the processor multiplier. The memory bus speed is the processor’s “external” speed, the speed it talks to the rest of the computer at. The memory bus speed also (normally) dictates the speed of the PCI local bus. This ratio of PCI bus speed to full system bus speed is controllable on most motherboards today. Typical bus speeds are 66, 75 MHz, 83MHz, 100MHz and 133 MHz bus speeds. The multiplier represents the number by which the memory bus speed must be multiplied to obtain the processor speed. Multipliers on PCs range from 1.5x to over 20X, though faster processors will eventually increase this unless the normal system bus speeds increase even higher.

Most chipsets will allow you to adjust both the system bus speed as well as the multiplier. In fact, adjusting these two settings is the basic methodology behind system overclocking. It is important to note that adjusting the multiplier on many systems has no effect at all because the processor itself is “clock-locked”, meaning it is wired to only allow one multiplier. This is the manufacturers’ way of trying to make overclocking harder. Of course, the consumer market as devised ways to get around this clock lock on some processors, such as the Athlon XP. If one is successful in over-riding this lock, the chipset will again be able to dictate the multiplier.

The bus speeds and multipliers a chipset will support plays a large role in dictating what processors it will support as well as how much expandability room you have for the future. 

Multiple Processor Support

Some chipsets support the ability to make motherboards that support two or four processors. The chipset circuitry coordinates the activities of the processors so that they don’t interfere with each other, and works with the operating system software to share the load between them. The standard for multiprocessing in Pentium and Pentium Pro PCs is Intel’s SMP (symmetric multiprocessing). It only works with Intel processors. Of course, I should make note that, in order to successfully have a multi-processor system, that much more than a supporting chipset is needed. You must have compatible CPU’s and a supporting OS.