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The Microprocessor

The CPU (Central Processing Unit)is the 'chip' that controls all that goes on in the computer. The original IBM PC's contained an Intel 8088 processor with a clock speed of 4.77 Mhz.
The later IBM XT, which first came on the market in 1984, was based on the 80286 microprocessor running at a clock speed of 6Mhz. The more advanced AT computer, being faster, was able to move around larger 'chunks' of data. Intel continued with the 80x86series of microprocessors through the 80386 and the 80486. Effectively the pentium is a 80586.

If you purchased your computer a few of years ago it will most probably be of the 486 type, perhaps running at a speed of 25, or 33 Mhz. Prices of the 486 100Mhz can now be purchased for about  £15 and worth considering if you do not want to purchase a Pentium mother-board just yet. But, with the prices of the Pentium mother board now about £60 that is a option considering for your "cheap" upgreade. For an overall outlay of £120 you can upgrade to a Pentium 266Mhz machine.

Intel began shipping the Pentium Pro in 1996 with MMX extentions being added to the family in 1997. The Inel C233Mhz-MMX CPU can at present be purchased for about £80 but this price is falling rapidly. The other two options of the AMD C67 K6x86 266Mhz can be purchased for about £60, all inclusive of VAT.

If you wanted to go for a Petium P11 upgrade the prices of these are also coming down. The motherboards for these are about £100, for a P11 board up to P333, with the CPU costing about £120  for the Intel P11 Celeron 300MHz.

Replacing the CPU in the  is quite easy, with the base normally being a 'zero insertion force'(ZIF)socket, similar to the one in the diagram above right. It is nothing more than lifting the socket handle, removing the old chip and replacing it with the new one. The socket and the chip will have a mark on them indicating where to put the pins. If you are going to fit a 100Mhz 486, or a pentium chip, you will also need to fit the device with a small fan. Also check your motherboard user guide to see if you need to change any links to accommodate the higher clock speed. On my 486DX4 100Mhz machine this involved moving a link to change my CPU clock setting to 50MHz, and a clock selector link for clock speed increases above 33MHz. In all cases you normally need to check the links in the motherboard manual.

Always plan your upgrade by asking yourself how much more power do you need. There is always a temptation to upgrade just to bring it up to minimum specifications. Resist this if you can. Always try to identify more definite benefits within what you can afford.