Although the processor needs memory and other hardware to run efficiently, it is at the heart of performance. When the Pentium processor came out, it was called a Pentium because the number 586 was refused patent by the United States Government - they wouldn't let Intel copyright a number. Then there was PentiumI, PII, PIII - now there is P4.

Numbers like 1.8 GHz and 586 MHz refer to the clock speed of the processor. Clock speed means the number of pulses generated per second. Instructions are sometimes executed at a speed of one per clock pulse. Newer processors can perform more than one instruction per clock pulse. Clock speed is usually measured in MHz (megahertz, or millions of pulses per second) or GHz (gigahertz, or billions of pulses per second). The latest processors run at clock speeds of hundreds of megahertz and some exceed one gigahertz. The clock speed is regulated by a quartz-crystal circuit, similar to those used in radio communications equipment.

Read about the latest microprocessor chips here.
Intel are not the only manufacturers of processors: Cyrix and AMD are also well-known chip makers. There was great excitement when AMD broke the 1 GHz (Gigahertz) barrier last year. The AMD Duron 1.4 GHz processor performed better than Intel's 1.8 GHz processor, and it will be interesting to see whether Intel's P4 2 GHz can finally outperform it.

Look up a definition for "processor" on Whatis.com. This site is a great resource for ICT terminology.

Finally, does this mean that your "old" PI and even 486 machines are not useable? Not at all. The latest and greatest isn't necessary - merely desirable. Perfect graphics, big screens and superfast processing are things which most of us have to keep dreaming about.