The Central Processing Unit (CPU)

The CPU (Central Processing Unit) is the device that interprets and executes instructions. Mainframes and early minicomputers contained circuit boards full of integrated circuits cards that implemented the central processing unit. Today's single-chip central processing units, called microprocessors, make personal computers and workstations possible. The CPU has the ability to fetch, decode, and execute instructions and transfer information to and from other resources over the computer's main data-transfer path, the bus. By definition, the CPU is the chip that functions as the "brain" of a computer. In some instances, however, the term encompasses both the processor and the computer's memory or, even more broadly, the main computer console (as opposed to peripheral equipment).

All processors use transistors as switches to produce signals, much like a light switch, which digitises the information and breaks them up into small chunks. If you have one transistor you can perform two signals - on and off. If you have two transistors you can perform four signals - both on, both off, first on, second off, first off, second on. In binary this would read: 00111001 - zero for off, one for on. With only 32 transistors we can perform over 4 billion signals. The AMD K7 (Athlon) processor, for example, has 22 million transistors and is more powerful than all the mainframe computers of the 60s put together.

Clock Cycle

The clock cycle is the smallest unit of time recognised by the CPU, typically a few hundred millionths of a second. During this time the CPU performs the simplest of instructions. The speed of the CPU largely depends on how many instructions it can carry out during a single clock cycle. The speed of how many instructions can be carried out is measured in MIPS (Millions on Instructions Per Second). The fastest RISC chips can perform over 200 MIPS whereas Pentium processor performs only about 150 MIPS. Other speed factors depend on how many transistors can be combined on a processor and the frequency of the clock cycle which is measured in MHz (Mega Hertz) - the faster the better.

CISC / RISC

For a long time CISC (Complex Instruction Set Computing) processors were the only type of chips used in IBM compatible PCs. The Intel Pentium 2 has already made a good start towards RISC (Reduced Instruction Set Computing) and now even IBM compatible PCs enjoy the kind of power that Apple Mac users have taken for granted for years. Because the CPU doesn't know the location of each instruction it is supposed to carry out, every time it performs a task it has to sort through hundreds of instructions to find the ones needed to complete the task. This takes a finite amount of time that slows the CPU down. One way around that has been found in RISC chips. Having fewer and shorter instructions to sort through, RISC chips can run at higher speed than CISC chips.

Level 1 Cache

Imagine you sit in an audience of listeners. As the speaker at the front dispenses his/her material you absorb the new information bit by bit and process them as needed. In computing, as with humans, this happens in several stages. When you listen to someone speaking, all the average person can absorb are 2.5 words per second and remember them for about 5 seconds. Then the information vanishes again. But within those 5 seconds we can think about the information and evaluate them critically. That is exactly what the CPU does too.

Inside the CPU itself is a tiny amount of memory, just enough to absorb the information and remember them for long enough to process them further. The benefit of the Level 1 Cache is that it runs at the same speed as the processor itself. It is therefore the fastest and most efficient type of memory within a computer system and of up most importance for the CPU. For information about cache sizes, see the table below.

Level 2 Cache

Level 2 cache memory is a section of fast memory linking the CPU and the main memory. Like the level 1 cache, the level 2 cache temporarily stores data and instructions the CPU needs to execute upcoming commands and programs. Level 2 cache cannot be as fast as level 1 cache, but it is still considerably faster than the main memory. The level 2 cache system anticipates the data it will need through algorithms, putting it 'in the pipeline' as it where, for the CPU to request it. It is therefore also commonly referred to as 'Pipeline Burst Cache'. 

Cooling

Processors are build to operate at a certain temperature level. As processors become faster and their construction smaller and more complex, they build up a lot of heat which can in turn destroy the processor by burning it out. Processors are designed to cope with temperatures of up to 80șC. Once this level has been reached the life-span of the processor is reduced significantly. The heat sink and fan that are directly attached to the processor help to transport most of the heat off. Always make sure that your processor fan is in in good working condition, especially if you're thinking of overclocking your system.

Fitting

Depending on what type of processor you have, the fitting procedures are somewhat different. If you bought your CPU new, ask your dealer for the installation manual that comes with the chip, it's always a good reference.

As for the basics:

Any SocketX CPU will have a ZIF (Zero Insertion Force) socket of some kind and all ZIP sockets are the same. You open the lever and insert your CPU with its marked corner to the marked corner of the socket. Simple as that.

SlotX CPUs are somewhat different, in that they slot into their respective slots just as any other expansion card would. At the top of each type of SlotX CPU there will be two clips, rather similar to DIMM socket clips. Make sure that these are really clipped in perfectly in order to avoid problems.

As Intel has it, there is, of course, the Celeron, that fits both descriptions, as it's available as Slot1, as well as Socket 370 units. Each processor fill obey the standards described above. The question is: 'Would you really fit a Socket370 Celeron into its own native motherboard?' I'd rather use a BX (or higher) Slot1 motherboard and hope for future upgrades. Intel has foreseen the dilemma and has made an adapter available that bridges the two standards. The Socket370 Celeron will fit into the adaptor, which features a Socket 370 ZIF socket, and fits itself neatly into a Slot1 slot.