3 ms·
IIRC it's about clock speed. Your electrical signals travel at the speed of light. If you have a 4GHz clock the signal travels at 300,000,000 m/s. Now one clock
by carlmr 9y ago
IIRC it's about clock speed. Your electrical signals travel at the speed of light. If you have a 4GHz clock the signal travels at 300,000,000 m/s. Now one clock cycle is 0.00000000025s, so the light has time to travel 0.075m. That's only 7.5cm! And you need everything to be synchronized inside and get into a steady state before the next clock cycle.
- blauditore 9y agoElectrical signals don't travel at the speed of light, but your argument is still valid.
- jaytaylor 9y agoActually, they very nearly do. The speed of electricity in a 12-gauge copper wire is 299,792,458 meters per second x 0.951 or 285,102,627 meters per second. This is about 280,000,000 meters per second which is not very much different from the speed of electromagnetic waves (light) in vacuum.
- tlb 9y agoNot wires across silicon, which have higher capacitance and much higher resistance. For millimeter-long connections you might get 1/10 of C, ie 33 ps/mm instead of 3.3.
- jaytaylor 9y agoHey, that's actually really interesting, thanks for the followup! This corroborates what you're saying: https://www.reddit.com/r/askscience/comments/204hl2/at_what_speed_do_electrons_move_around_inside_of/ https://www.reddit.com/r/askscience/comments/204hl2/at_what_...
- deepnotderp 9y agoTransmission line signalling can get near speed of light in silicon. But it has its own issues :)
- deleted 9y ago[deleted]
- AstralStorm 9y agoThe synchronization can be avoided somewhat by the use of (also power efficient) asynchronous electronics. You can also employ lower frequency clock them multiply it on site. A bit more cost because now you have to handle clock jitter. And then we have computing separated by meters of wire and network fabrics in clusters. So size is not that much of a problem. It is just that free lunch for programmers has ended some 10 years ago.