You need a CPU (central processing unit), which is the so-called brain of the computer. It processes instructions given to it by software, such as your word processing or accounting programs. A computer also needs a place to store data. That's usually a magnetic hard drive.
<u><em>A CPU
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<u><em>A Motherboard
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<u><em>RAM
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<u><em>A Storage device
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<u><em>And a Power Supply
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<u><em>If you're referring to the elements?
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<u><em>Silicon, Gold, Silver, Copper, Aluminum(ium) Germanium, and perhaps various other elements.</em></u>