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As today's newest CPUs surpass the 1-GHz barrier, it's easy to get frustrated with the older, pokier processor in your PC. A CPU upgrade kit can give your older machine a reasonable performance boost for a practical price.

If your PC uses a Socket 7 processor and currently runs at between 75 and 233 MHz, you can upgrade to an AMD processor that runs at 333 MHz for about $100 or at 400 MHz for about $130.

Most upgrade processors are designed for Slot 1 PCs that use early Intel Celeron or Pentium II CPUs in the 233- to 450-MHz range. An upgrade to 600 MHz will set you back $249 if you have a Pentium II PC, or $220 if you own a Celeron. Stepping up to 700 MHz costs $320, and jumping to 800 MHz runs about $400.

Most contemporary Intel-based motherboards use Socket 370 for their CPU. If you purchased one of the early Celeron-based systems that use Socket 370, upgrades are now available. You can boost your PC to 566 MHz for about $240.

But consider carefully whether an upgrade makes sense for you. While an upgrade processor can double your CPU speed, an old hard drive or video card in your PC can limit the overall performance boost to as little as 25 percent. Sometimes a new PC can be the best deal of all.