CPU stands for Central Processing Unit. A CPU is essentially the brain of your computer. Its job is to process the instructions contained within computer programs. Modern CPUs are microprocessor chips that attach directly to the motherboard. The speed of microprocessors in PCs is measured in megahertz (MHz) or gigahertz (GHz).
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The primary manufacturers of CPUs for personal computers are Intel and Advanced Micro Devices (AMD). Intel's processors include the inexpensive and basic Celeron and the more popular Pentium. Intel's top of the line processor is Core, which comes in Duo, Quad and Extreme versions. AMD's basic chip is the Sempron. The Athlon compares to Intel's Pentium in terms of speed and performance. Phenom is AMD's top of the line processor for desktop computers.
A microprocessor chip is a small piece of silicon containing thousands, hundreds of thousands or even millions of tiny transistors. Most chips have an arithmetic or logic unit which can perform mathematical calculations. The control unit takes instructions from the computer's RAM for processing.
CPU chips are generally very small and very thin, often less than one micron. Every modern CPU has a cache, which provides a buffer while the processor communicates with the computer's memory. The clock speeds of modern CPUs can currently reach 3 GHz and higher. CPUs also have a front side bus (FSB) speed which can greatly affect performance. CPUs can only be installed on motherboards with the same socket size. If you're upgrading or building your own computer, view the documentation that came with your motherboard or contact the manufacturer to determine which CPU to install.
In 1971, the Japanese company Busicom requested that Intel design twelve different chips for their calculators. Intel instead designed a group of four chips that could do the job of all twelve chips. The CPU was the Intel 4004, the first microprocessor chip. The 4004 differed from previous chips in that it was user-programmable. It was one of four chips dubbed MCS-4. Along with the 4004 CPU chip was a read-only memory (ROM) chip, a random access memory (RAM) chip and a register chip for input and output (I/O).
CPUs become obsolete very quickly. When you're considering buying a new computer or doing a CPU upgrade, it's important to purchase the fastest CPU you can afford. Recently multi-core processors have come onto the market. These outperform single-core processors because they function like multiple processors combined into one. They are especially useful for multitasking. However, these will also be obsolete within 5 to 10 years. Future processors will likely contain 30 or more cores in one chip.