5 ms·
Ask HN: In modern CPUs how many μs to flip a NAND (or other) logic gate?
- josh-wrale 10y agoI suspect it's actually better measured in femtosceonds, but either way is good.
- Majster 10y agoCan you be a bit more specific? You mean how long a NAND gates takes to "execute" a NAND operation? It's somewhere around 20 nano seconds.
- josh-wrale 10y agoYes, your version of the question matches what I'm seeking. 20 nano seconds. Thank you!
- alain94040 10y ago20ns corresponds to 50 MHz. Recent CPUs run at over 1 GHz, so 20ns is completely off. And the clock frequency includes many gates on its critical path.
- nicholas73 10y agoFor logic gates there is a "setup" and "hold" time (logic level prior to gate flip, then hold that level) for an operation to be successfully performed and transmitted to the next stage. It should be in the chip's datasheet (if you wanted a precise and specific number). If you don't care about logic transmission and just want "flip" then look at the rise/fall time.
- samfisher83 10y agoIt depends on PVT. Process, Voltage, and Temperature. When chips are being synthesized all this is characterized for each logic cell like and gates, flip flops, etc. They are in .lib files that is sent into the synthesis tools. If you can get one of those files it will tell you all the numbers.