GCC and static analysis
Posted Apr 29, 2012 10:45 UTC (Sun) by khim
In reply to: GCC and static analysis
Parent article: GCC and static analysis
Nit: Wasn't it quantum tunneling effects and resultant current leakage that killed the MHz war?
Nope. These can and do limit speed - but this limit is near terahertz. Worse: this limit have not stopped growing in the last decade: it went from about 100MHz to 800MHz+. Yet CPUs have stopped at 4-5GHz. Pentium4 was famously unable to reach this limit (fastest model reached 3.8GHz) while POWER6 (with it's entirely different architecture) stopped at 5GHz.
There are many different processes which limit the speed of CPU but they all are related to propagation of signals - and these are measured in fractions of speed of light. Refractive index of silicone is large (about 4, but, as usual, it depends on frequency) while refractive index of copper is low (about 1.10 - but, again, it depends on frequency). In the end the fact that at frequency of 100GHz speed can only pass 3mm in vacuum means working CPUs can not be built at this frequency.
Note that frequency of x86 CPUs is still incresing - but at totally different speed. Nehalem reached 3.86GHz at 45nm (Core™ i5-680) while Sandy Bridge reached 4GHz at 32nm (Xeon® E3-1290). You may say that it's limited by thermal envelope (as current leakage will predict), but I'll just point out that Core™ i5-680 is dual-core CPU while Xeon® E3-1290 is quad-core CPU. Where is my single-core 6GHz CPU? I know a lot of guys who'll be ready to pay good money for such a beast.
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