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As you can easily tell on most keyboards, it'll beep when you hold down combinations of keys, such as all four arrow keys. I've seen two answers: ghosting and the BIOS buffer.

Ghosting
This seems to explain it perfectly, but I've seen the argument that it no longer applies to most new keyboards. Indeed the ones at my school are old, and beeped when the arrows, or other sets of keys were pressed. However, the one in my new laptop (and with the price, you'd expect it to follow suit if that were true), does not beep at all. To confirm the problem, I made a simple program to tell me which keys were currently held down. Pressing things like C+F+V yields only two, so it seems to hold. Strangely enough, the four arrow keys worked perfectly. Wikipedia seems to approve this explanation, too.

Buffer
This also makes sense, especially after the argument that when the computer freezes up, anything you type will cause a beep due to the keystrokes in the buffer still not having been handled. But from the first example, the F+C+V is only three keys. As well, pressing, for example, the numbers atop the letters yielded varying numbers of keys being held down. Sometimes holding 1-6 yielded three of them, and sometimes all six.

What's really going on here?

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Sorry, but what was your question? –  Zoredache Jul 13 '12 at 17:24
    
@Zoredache, I've seen evidence for both of these. Which one (or how much of either) is actually happening? If it's the underlying problem you don't get, keyboards often can't handle more than a few keys being pressed at once, depending which ones you press. The two explanations I've seen for that are ghosting and the BIOS keyboard buffer, but I'm not sure which one's actually coming into play. –  chris Jul 13 '12 at 17:27
    
Your question still doen't make sense, both of those are real and can really happen. Ghosting has is a side effect of how keyboards are wired internally, buffers are used when a computer cannot respond to keyboard input fast enough. –  Zoredache Jul 13 '12 at 17:32
    
@Zoredache, I've seen people claiming that ghosting no longer really applies to keyboards any more, and that it's all the buffer, but I've seen evidence that each are playing their part, but also that the other might not be. For example, C+F+V (3 character keys) yields symptoms that could be for either, yet sometimes all of the numbers from 1 to 6 (6 character keys) can be held without those symptoms, going against the buffer. If the buffer isn't it, though, why would it happen when the computer can't process them because it's freezing up, despite only pressing one then? –  chris Jul 14 '12 at 19:34

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