A Wikipedia article on Power engineering reads,

Most refrigerators, air conditioners, pumps and industrial machinery use AC power whereas most computers and digital equipment use DC power.

As far as I know, all digital stuffs require DC power. AC power isn't particularly useful for digital computers, right? What does "most computers and digital equipment use DC power" imply or mean? Does that mean there are computers and other digital electronic gadgets out there which runs on AC power?

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    $\begingroup$ It would be helpful if you also add the link to the Wiki-article. $\endgroup$ – Bernhard Apr 1 '12 at 19:29
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    $\begingroup$ The author was just trying to be careful. I don't think there is any piece of digital electronic running on AC. Digital is in most case represented by different voltages. So if the input voltage oscillates it is hard to define 0 and 1. If you include a thyristor into the definition you could argue that it 'runs' on AC. $\endgroup$ – Alexander Apr 1 '12 at 21:19

Your question is the result of a poor wording choice by the Wikipedia author. While it may be possible to create a digital computer that makes use of AC power, none do. The power supply in modern desktop computers use a transformer and rectifier (and some capacitors for smoothing) to provide a constant, smooth $12\, \mathrm{V}$ DC current for the computer to run on.

To complicate things a bit though, many of the very high frequency serial buses used by a computer (Ethernet, Serial ATA, PCI Express, etc.) are essentially digital signals encoded in via an AC circuit. This is the result of trying to squeeze the maximum information capacity for a given bandwidth (see Shannon-Hartley theorem).


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