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The Central Processing Unit (CPU)

What is a CPU?

The Central Processing Unit (CPU) is a highly sophisticated set of Integrated Circuits (IC) on a single silicon chip - hence it it also know simply as the Chip. It is also known as a processor. The CPU is where instructions (-for example, of the operating system or an application) are run (executed). Each instruction is loaded in sequence into the CPU from the RAM and then carried out. Without the CPU, the computer will not do anything - except consume electricity!

Without the CPU, the computer will not do anything - except consume electricity

Due to the mass of circuits packed tightly inside the CPU, it is normally topped by a heatsink (-a passive cooling device designed to thermally conduct heat away from the chip) and, on top of that, normally an electrically operated fan. In the picture below, the chip is totally obscured under the fan housing and (below that), the finned heatsink:

A Typical CPU heatsink and fan

Manufacturers and Processor Family

There are many different chip manufacturers out there but, these days, home users realistically only have a choice of two:

Each of these these companies will have multiple chip lines or families (-this would be analagous to "car model" in the automotive industry), for example:

  • Intel sell the following processor lines (-not an exhaustive list by the way):
  • Similarly, AMD (Advanced Micro Devices) are currently marketing the following lines for home users:

Within each of these chip lines there are a number of processors (-think "trim level"), for example within the AMD Sempron line, there are no less than 37 processors, running at from 1.6 to 2.3GHz in speed and consuming from 35 - 62W of power!

Choosing a CPU

As you can see from the above, there is an awful lot of choice out there! Which CPU you opt for depends mainly on the following (-in order of importance):

.. the fastest processors will be those with the highest clock speed and largest numbers of cores ..

  1. The processor must be compatible with the socket on your Motherboard. If you are buying a new motherboard, it should state which socket is used - for example socket AM2 / AM3 (AMD) or Socket 778 (Intel). If you are using an old motherboard, you will need to find out which socket you have (-looking at the top of the chip should at least define if the chip is Intel or AMD). The motherboard may also have the socket number stamped next to the processor but the best way is probably to type in the product number of your PC (-normally found on the reverse side) to your favourite search engine and let the web do the work!

  2. What you need the PC for: if all you want it for is writing letters and surfing the web, then you do not need a particularly powerful chip but if you are going to be running the latest 3D rendering games then you will. In general the higher the clock speed, the faster the processor (-so 3.0GHz is faster than 2.8GHz) and the higher the number of cores the more tasks it will be able to handle simultaneously. As a result, the fastest processors will be those with the highest clock speed and largest numbers of cores. If you need to make a compromise, then go for a slower clock speed with more cores as this will generally outperform a faster single core (-unless you only ever run one program at a time!)

  3. Price: the faster processors will be the most expensive. There is generally a price premium to the leading edge processors, so it is normally best to consider those a little behind the zenith, unless money is no object..

  4. Power consumption: if you will be running the PC away from home a lot (laptop), using it a server which is "always on" or are just worried about your carbon footprint, then you should consider a processor with a low wattage (power consumption). Low wattage CPUs will also run cooler, meaning less heat related problems. However, lower-power chips tend to have slower clock speeds and are more expensive to buy than their power-hungrier siblings

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