Here's our Hardware Tip for.. February 5, 1999
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CPUs (Central Processing Units)
The CPU (central processing unit, also called the microprocessor) is where all the calculations take place in a PC. CPUs come in a variety of shapes and sizes. The most common in today's PCs are the PGA (Pin Grid Array) and SEC (Single Edge Cartridge). The Intel PII for example, is of the SEC type.

Modern CPUs generate a lot of heat. To cool the CPU, a cooling fan or a heatsink is attached (This cooling device is usually removable, although some CPU manufacturers sell the CPU with a fan permanently attached.

CPUs have a make and model, just like an automobile. When talking about a particular car, most people speak in terms of a Ford Taurus or a Dodge Caravan when they talk about CPUs; it's an Intel 486 or an AMD K6. Some of the more common makes are Intel, AMD (Advanced Micro Devices), and Cyrix. Some of the more common models are 8088, 286, 386, 486, Pentium, Pentium Pro, Pentium II, K5, K6, and 6x86, although these days, most people run Pentiums or better. In the early years of CPUs, makers would sometimes make the exact same model, so you could get an AMD 486 or an Intel 486.

This is no longer true, although some models are very similar, such as the Intel Pentium and the Cyrix 6x86.

CPUs have a "top speed", which is determined at the factory. It is called the clock speed and is measured in megahertz (MHz). The first CPU used in PCs had a clock speed in the range of 4.77 MHz. Today's CPUs have clock speeds up to 500 MHz. When talking about a CPU, people often cite the make, model, and clock speed, for example, an 180-MHz Intel Pentium Pro. CPUs of the same make and model are produced with many different clock speeds. For example, the Intel Pentium Pro comes in three different speeds: 166, 180, and 200 MHz. The main reason for picking one speed over another is primarily the thickness of your wallet.