When you're buying new parts it is important to understand what you will need and what is recommended. While that criteria will change from time to time, the spirit remains the same. The most confusing part of buying new computer components is undoubtedly the issue of memory type, frequency, and the speed of the frontside bus (FSB). This article will outline these terms and explain what you'll need to know to make an informed buying decision.

To begin with, the frontside bus is the physical pathway between the CPU and the RAM controller. AMD64 (Athlon 64, Opteron, and Athlon 64-FX) processors have integrated memory controllers, meaning that there is no FSB, technically. Instead, AMD64 processors are measured by their bus speed, which is determined by the number of HyperTransport links that they employ.

The frontside bus operates at a certain frequency. These days it's 400mhz, 533mhz, and 800mhz for Intel-based motherboards. A motherboard will generally support a range of FSB frequencies, although some of the later models will only do 800mhz due to other architectural constraints (a different socket type). The socket 478 Intel processors are 400mhz for the earlier Northwood A processors up to 2.4ghz and for Celeron processors, 533mhz for the 2.26 to 3.06 Northwood B processors, and 800mhz for the Northwood C. The Prescott core uses an 800mhz frontside bus only, and is available in both socket 478 and socket 775 packages. The number refers to the number of contacts or pins that a processor has, and motherboards will only support one type. So if you want to go cutting edge, you'd want a socket 775 processor and a motherboard that will support that. Since there is only one FSB frequency in that package, you have nothing to worry about in terms of compatibility with supported motherboards.

For socket 478 processors the story is different. Since there are two different cores in production and three different FSB speeds, you will have to make sure your motherboard will support the processor you want to use. If you're going to go with a Celeron processor, you'll need a motherboard that supports a 400mhz FSB. To find out which motherboards can use that processor, you can look at the motherboard manufacturer's Web site and that will usually tell you what you need to know.

Alternatively you can look at the northbridge chipset that the motherboard uses and generally determine from there what it supports. Here is a list of northbridge chipsets and the frequencies they support:

Please note that chipset support is not always indicative of what the motherboard will accept, specifically when it comes to AMD64 processors. There are three socket designs for AMD64: socket 754, socket 939, and socket 940. The 754 is the Athlon 64; the 939 is the new generation of Athlon 64-FX (the first generation, FX-51, was 940); and the 940-pin design is for the Opteron. While all AMD64 chipsets will support all three designs, motherboards can only support one, so make sure you've got the right socket for the right processor.

I didn't list DDR266 and DDR200 support because these RAM speeds are effectively obsolete. You're better off buying DDR333 for a 266, 333, or 533 FSB processor, and DDR400 for anything faster. Beware the socket 775 motherboards, which will support either DDR or DDR2, but not both.

The Northwood A is usually marked either with an A after the speed raing (as in 2.4A) or not marked at all. The Northwood B core is marked with a B after the number, likewise with C. The Prescott socket 478 is marked with an E at the end of the speed rating, as in 3.2E. Other ratings are for the Extreme Edition processors, which are now discontinued.

Inevitably there will be someone who doesn't see a chipset listed here that they want to know about. My advice is to go to the VIA, Intel, SiS, ATI, and Nvidia Web sites to look up the information you need.

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Copyright 2004 Jem Matzan. Verbatim copying and redistribution of this entire article are permitted without royalty in any medium provided this notice is preserved.