What is the absolutely fastest way to output a signal to external hardware in modern PC? [closed]

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I was wondering, what is the absolutely fastest way (lowest latency) to produce external signal (for example CMOS state change from 0 to 1 on electrical wire connected to other device etc.) from PC, counting from the moment, where CPU assembler program knows that signal must be produced.

I know that network device, usb, VGA monitor output have some large latency comapred to other interfaces (SATA, PCI-E). Wich of interfaces or what hardware modification can provide a near-0 latency in output from let's suppose assembler program?

Answer 1

I don't know if it is really the fastest interface you can provide, because that also depends on your definition of "external", but http://en.wikipedia.org/wiki/InfiniBand certainly comes close to what your question aims at. Latency is 200 nanoseconds and below in certain scenarios ...