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Small correctionSmall correctionPosted Oct 2, 2007 0:27 UTC (Tue) by Richard_J_Neill (subscriber, #23093)In reply to: Small correction by khim Parent article: Memory part 2: CPU caches
Not quite - we aren't limited by speed of light, but by power dissipation. One could certainly fit 100GB of RAM inside the 5cm boundary, by making a 3-dimensional structure. However, there would be no way to keep such a solid "brick" of transistors cool...
[Of course, I hope to be proved wrong in that!]
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Small correction Posted Oct 2, 2007 4:54 UTC (Tue) by AJWM (guest, #15888) [Link] > However, there would be no way to keep such a solid "brick" of transistors cool...
That's where research into new substrates comes in. Synthetic diamond, for one example (diamond being an excellent heat conductor). (Hey, you didn't think the fancy crystalline computer modules in various SF TV shows were just glass, did you?)
Hot? Posted Oct 2, 2007 21:06 UTC (Tue) by ncm (subscriber, #165) [Link] Who says memory has to be made of transistors? In the past, memory has been made of ripples on mercury, ferrous donuts, rotating drums, holes in paper, glow in phosphors bombarded by electron beams... storage need not run hot. In particular, bits not changing state need not consume any power. Changing state may take arbitrarily little power; the faster they must change, the more power it usually takes, but write speed is less critical than read time. Interacting with it is always going to take power and produce heat, but that may be much, much less than with masses of transistors.
Hot? Posted Oct 4, 2007 13:14 UTC (Thu) by ekj (guest, #1524) [Link] Actually, that's not true. Bolzmanns constant sets an absolute, physical, lower limit on the amount of power that is needed for causing a permanent lasting state-change. (such a flipping a single bit)
Granted, that limit is *very* low. But it's not zero. I calculated some time back (if you're sufficiently interested, google it) that if we continue doubling computing-power we'll run up against this hard physical limit in aproximately 15-20 years.
That's a long time in computing. But it's not forever. It's short enough that most of us will get to experience it.
Oh yeah, I'm aware of reversible computing. I just don't think that'll go anywhere. I'd be happy to be proven wrong.
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