The parts - processors

The processor is the brains of your computer and contains the logic circuitry to perform the instructions of a computer's programs. A processor has three main tasks: it reads data, it manipulates data, and often it writes data to memory.

One of the most important differences between motherboards is that each will only support certain types of processors, for example, a Pentium 4 or an AMD Athlon 64 chip. This is because different chips have connectors that vary physically from one another. Each motherboard has a specific type of CPU socket, and only processors that fit in that socket can be used on that particular motherboard.

This is an important thing to remember, particularly when you're looking to build your own setup or are upgrading your existing system, because the type of processor you buy will impact on which motherboard you choose and vice versa.

Socket formats

Up until a couple of years ago, processors conformed to the same motherboard Pin Grid Array (PGA), called Socket 7. The processor itself was square and encased in a plastic cartridge. On the bottom was an array of pins that connected to parts of the processor and allowed the chipset to control the chip's operation.

Since then, processors have come a long way. Nowadays, there are five types of sockets you will commonly encounter, denoted by the number of pins in the socket:

  • LGA755. Used for nearly all current Intel processors, including the Pentium 4 5xx, 6xx and 8xx ranges, along with the Celeron 3xx range and the Pentium D 8xx and 9xx ranges.
  • Socket 478. Used for older Intel Pentium and Celeron processors. It has become increasingly rare as the older processors are phased out.
  • Socket 754. Used for AMD Sempron and a limited number of AMD Athlon 64 processors. Only the slower Athlon 64s use this and these CPUs do not support dual channel memory configurations.
  • Socket 939. Used for the faster AMD Athlon 64 processors, along with AMD Opteron and Athlon 64 X2s. These CPUs support dual channel memory configurations.
  • Socket A. Used for older AMD Athlon XPs and Duron processors.
It's absolutely vital that you get a motherboard that matches your processor type. If you're buying an Athlon 64, be particularly careful, since this type of processor comes in two different socket types, depending on the speed. For instance, the Athlon 64 3400 fits in a Socket 754, while the Athlon 64 3500 plugs into a Socket 939. The Athlon 64 3200 can be bought in either a Socket 754 or 939 form. Our general recommendation is that, if you plan to buy AMD, get a Socket 939 motherboard and processor, since that gives you headroom for future expansion and more advanced capabilities, such as the ability to implement dual channel memory configurations, which noticeably improves system performance.

Intel processors

Pentium 4 Processor

In 2004 Intel changed its processor number scheme, abandoning the GHz rating in lieu of an abstract model numbering scheme. Now Intel processors are arranged in families, such as the 3xx (Celeron), 5xx (Pentium 4), 6xx (Pentium 4 EM64T) and 8xx (Pentium 4 dual-core) families. Within a given family, the higher the number, the faster the processor; for instance the Pentium 4 660 runs at 3.6GHz, while the Pentium 4 630 runs at 3.0GHz. If you find the new numbering scheme confusing, don't worry - most sellers will be more than happy to tell you the GHz speed of any processor they are selling.

The four main families of Intel desktop consumer processors break down as follows:

  • The Celeron (3xx) processors are entry-level CPUs, designed for low-cost systems. They don't have as much internal memory ("L2 cache") as other Intel CPUs.
  • The Pentium 4 (5xx) processors are the mid-range processors. They are faster, on a clock for clock basis, than Celerons, but lack 64-bit extensions.
  • The Pentium 4 EM64T (6xx) processors have 64-bit extensions, similar to those found in the AMD Athlon 64. They're best used with the new 64-bit version of Windows XP, which can make the most of their extra power.
  • The new Pentium 4 Extreme Edition dual-core (8xx) range as well as the Pentium D (8xx and 9xx) range, essentially have two 6xx processors on a single packaged chip, effectively making the system a dual-processor system (even though it only has "one" CPU). The Pentium 4 dual-core processors require motherboard with a supporting chipset, such as the Intel 945/955X chipsets. The nForce4 SLI chipset also supports dual core CPUs, but it is up to the motherboard manufacturers to implement this feature of the chipset. Double check on the vendor's website to make sure the particular board you are after does support dual core.

All of these current Intel processors fit into LGA755 motherboards, although you will need a supporting chipset if you plan to install an 8xx processor.

AMD processors

In its consumer line of products, AMD has boiled its vast collection of different products down into three core models: the Sempron, the Athlon 64 and the Athlon 64 X2. You may still see the rare Athlon XP around, but we recommend avoiding them.

AMD has an unusual naming schema, basing its product names not on the actual GHz rating of the processor, but on the GHz rating of an Intel processor of equivalent speed. For instance, the Athlon 64 3000 only runs at 2.16GHz, but because it is as fast a 3.0GHz Intel Pentium 4 (because of improved processing efficiency), AMD call it the Athlon 64 3000. This is done to reduce confusion for buyers deciding whether to buy Intel or AMD. And if you're worried that AMD are highballing their comparative speeds, don't be - if anything, the AMD processor speed equivalents are conservative. As an added bonus, the naming schema aligns the AMD processors, making it easier to choose between different types of AMD processors (for instance, it makes it easier to decide whether to buy Sempron or Athlon 64, because both processors are rated on the same scale).

  • The Sempron is AMDs answer to the Intel Celeron. It's a very low cost processor based on the Athlon XP. It lacks 64-bit extensions. It fits in a Socket 754 motherboard.
  • The Athlon 64 is AMDs mainstream and high-end processor. It has 64-bit extensions (which require the new 64-bit version on Windows to make the most of). Some use 754-pin sockets, others 939. Check which you have before buying your motherboard.
  • The Athlon 64 X2 is a dual-core processor, integrating two Athlon 64 CPUs on a single piece of silicon, effectively making it a dual-processor system on a chip. Unlike the Intel dual-core solution, the X2 does not require a special chipset, and should run on any Socket 939 motherboard (although, at the time of writing, the X2 had not been released, so we cannot confirm that every Socket 939 motherboard supports it).

Dual processors and dual-core processors

Dual processor motherboards are usually only found in server setups and high-end desktop PCs that use the functionality for intense graphics CAD and design work. Therefore, dual processor boards aren't really applicable to the consumer desktop PC market. However, the recent introduction of dual-core processors by both Intel and AMD is bringing multiprocessing to the masses.

A dual processor system is exactly what the name implies - a system with two processors. You need a motherboard with two processor sockets to make this work (and such motherboard tend to be expensive). A dual-core processor is a little different, however. A dual-core processor is a single chip that has multiple processing "cores" on it. It will appear to the operating system as two processors, act the way two processors would act and have the same kinds of advantages as a dual-processor system has. It is only one chip, however, and only requires a single standard socket on the motherboard.

AMD's Athlon 64 X2 (which has the memory controller on the chip), should work in any Socket 939 motherboard. Intel dual-core processors (which leave memory control to the motherboard's chipset) require a supporting motherboard.

By next year, both Intel and AMD expect that the bulk of processors shipped will be dual-core models.

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