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Ok, before Weztel can get to it, RISC is reduced instruction set computing, or something along those lines, and CISC is complex instruction set computing.
The difference is that a risc processor can only do simple calculations. Like addition, subtraction.... stuff like that. When the computer code is compiled, the compiler translates the code the programmer wrote into code that's very simple. This allows the processor to be smaller and less complex, and it also doesn't take as long because it doesn't have to choose from as many instructions as a CISC processor. The downside, you have to put the processor through more clock cycles to do a problem. But because it takes less time to run through one clock cycle, it makes up for it.
CISC processors take a problem and crunch the entire thing. Because of this, a CISC processor has a large number of instruction sets to choose from, and takes more time per clock cycle. But, when it decides what to do with it, it can crunch the entire thing at once, instead of little pieces.
So who uses what processors? Mac's use RISC, and PC's use CISC. Sun Systems also use RISC processors, and run Sun's version of Unix. (I also add that they are faster then both Mac's and PC's)
In the end, RISC is faster. But as I've said already, Intel and AMD processors are no longer pure CISC chips.
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