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The reason CPUs aren't getting any faster is only tangentially mentioned in the article. Yes, it is heat dissipation. But why then did they get faster for so
by 1053r 16y ago
The reason CPUs aren't getting any faster is only tangentially mentioned in the article. Yes, it is heat dissipation. But why then did they get faster for so many decades?
As the process size drops, you can crank up the clock-speed while leaving the total heat dissipation constant. But the heat density is related to the voltage, resistance, and the amount of time the transistors spend partially on or off (we wish they were perfect switches, but they aren't really). So as you switch faster, unless you can lower the resistance or voltage (which requires changing your materials), you probably spend more and more time in a partially on or off state. This means your heat density rises to the point where you are just south of burning things out.
You make some engineering decision about the reliability you want in your chips, and calculate or test how high a heat density you can tolerate. But unless you change your materials so they use lower voltage, or invent new ways to move heat away faster, or use materials that are more conductive, you aren't upping the heat density or clock rate. But you can still make them smaller and use less power total for the same amount of computation.
This is why reversible computing (gives off less heat), diamond substrates (much higher thermal conductivity), microfluidic channels (moves heat away faster), and parallelism (larger chips = more computation) are being explored. And only the last one is practical THIS year.
- borisk 16y agoIMHO the real reason is CPUs and manufacturing technologies have become extremely complex. So although there are known, simple ways to address the heat dissipation it takes a lot of time to implement them.
- Symmetry 16y agoAnother reason we've stopped getting faster is that we've reached a point where velocity saturation in silicon has become an important issue: http://en.wikipedia.org/wiki/Velocity_saturation http://en.wikipedia.org/wiki/Velocity_saturation
- seancron 16y agoWe're quickly reaching the limits of silicon-based chips, but new materials will allow us to make even faster CPUs. One such material is the material that won the Noble Prize in physics: graphene. Graphene can increase the frequency of an electromagnetic signal, which can allow for even faster CPUs in the 500-1000 Ghz range Source: http://web.mit.edu/newsoffice/2009/graphene-palacios-0319.html http://web.mit.edu/newsoffice/2009/graphene-palacios-0319.ht...
- _delirium 16y agoIt's not clear that a whole CPU can actually be made at anything near 500-1000 GHz, though. That's the switching speed of the graphene transistors themselves, but the clock speed of a processor can't really feasibly be made to be equal to the switching speed of the transistors. There are silicon transistors with 50 GHz switching speeds, but the CPUs are still plateauing at around 4-5 GHz.