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Central Processing Unit (CPU)

A Central Processing Unit (CPU), often just called a processor, is the brains of your computer. It is considered to be a logic machine, where it is not particularly smart or capable of independant thought but quite capable of executing a series of logical instructions called a program. The CPU fetchs its next instruction from memory, decodes it and breaks it into parts that are dealt with by different parts of the CPU, executes the instruction accordingly and writes it back to memory. This is considered to be one instruction cycle and once complete the CPU then commences the next instruction cycle and continues rapidly in this fashion.

There are several manufacturers of processors however in desktop and laptop computers the two that we encounter the most are Advanced Micro Devices (AMD) and Intel. When selecting a processor there are a number of factors to consider, one of the more important being the CPU socket type as this must be the same as the motherboard you are using or the CPU will simply not connect to it. AMD and Intel use very different types of CPU sockets and the CPU you purchase will determine which motherboards you can use and vice versa. To complicate matters further as CPU's have evolved the socket type they use has changed to accommodate new features and older motherboards will generally not support the later processors from the same manufacturer.

A heatsink and a cooling fan are mandatory for a CPU and almost all CPU's come packaged with a manufacturer approved heatsink/fan combination. The CPU socket type of the procesor will determine the type of heatsink that you need to use. Beware of aftermarket coolers as not all of them cool as efficiently as the standard items and an overheating processor will have a short life, give eratic machine operation and will suffer from degraded performance. The cooler a cpu runs the better it will perform when under load. Be aware that if you start up your computer without a heatsink on the processor it will last 30 seconds at the very very most. I have seen them glow red in under 10 seconds.

Other features to be considered when selecting a procesors are performance factors such as speed, number of cores and cache size. A CPU's speed is measured in gigahertz (for example, 1.8ghz, 2.2ghz, 3.2ghz etc) and this is a reasonable general guide to its overall performance however other factors such as number of cores need to be taken into consideration. A dual core CPU really has two processors built into the one processor package and a quad core CPU has four. Multiple CPU cores show their highest advantage when you are using more than one program at the same time, effectively sharing the work between the processors rather than making one processor do all the work. Cache size refers to the amount of memory that the CPU has built into it. Often when executing a series of instructions the CPU may need to use the result of a previous instruction in its next cycle and cache allow the CPU to store these results within itself rather than having to send it to the RAM and then retrieve it again, allowing for faster execution.

When time comes to purchase a CPU and motherboard there are a few different approaches you can take. Some computer enthusiasts, particulary hard core gamers, will specifically select a motherboard and CPU often spending hours poring over manufacturers websites checking CPU support lists for high performance motherboards that suit the biggest processor that they can afford and having their hardware vendor (usually the local computer shop or online computer store) find out its price and availability. If you are building a general purpose or office machine this level of diligence is pointless and you are better off discussing with your vendor what they have available. This will allow them to guide you as to compatibility and will also keep the price of the machine down as you will not be charged for their additional legwork. Be a good hassle-free customer to them and they will reward you in kind.

Installing a CPU

Installing a central processing unit is remarkably easy but care should be taken as they are reasonably fragile and expensive. Older CPU's have a series of pins that are inserted into the cpu socket and these were quite fragile and prone to bending if mistreated. Newer cpu's have the pins on the socket and the cpu itself has flat faces that these pins correspond to and no socket holes, a more robust arrangement. For our example we shall examine the installation of a socket 775 cpu into a motherboard.
Installing a CPU
  1. The contact points (shown) should be face down on the motherboard mating to the pins inside the CPU socket. Note the two notches on the edge of the CPU to ensure that it is installed correctly, these line up to corresponding protrusions on the CPU socket.
  2. Gently place the CPU into the CPU socket ensuring the notches are correctly oriented.
  3. Swing the load plate on its hinges onto the CPU
  4. Then move the locking lever onto the locking plate and make sure it clips in properly.
  5. Place the CPU cooler and fan over the processor lining up its four legs to the holes on the motherboard. The legs tighten to the motherboard by pushing them down with your screwdriver and then once fully down rotating the 90 degrees clockwise. Do all four moving to opposite legs as you tighten them down. Removal is the reverse of installation.
  6. Finally, attach the cooling fans electrical connector to the appropriate header on the motherboard.