The only difference between a USB and PS/2 mouse is how the device connects to a computer.

PS/2 or USB?
PS/2 wins on three fronts: First, it supports full n-key rollover. Second, PS/2 keyboards aren't polled, but are completely interrupt based. And third, it is impossible for it to be delayed by the USB bus being used by other devices. There are two types of USB transfer modes - the interrupt transfer mode (USB polls keyboard, when key is sensed the USB controller sends the interrupt to the CPU), and the isochronous transfer mode, which reserves a certain amount of bandwidth for the keyboard with a guaranteed latency on the bus. Unfortunately, there are absolutely no keyboards made that use the latter, because special controllers would have to be used, thus making it cost prohibitive.

So if your keyboard supports both PS/2 and USB, and your PC has a PS/2 port, there's no reason not to use it.

Argumentet for PS/2 er at det ekstra halve millisekundet USB legger på latencyen på tastaturet er avgjerande.

Det halve sekundet mennesket bruker på å oppfatte ting på skjermen, og deretter trykke rett tast - det er derimot irrelevant. Tida det tar å polle tastaturet er ikkje tid i menneskeleg skala. Vi oppfatter det som synkront. Alt under 30 millisekunder er dønn synkront for mennesker.

http://www.humanbenchmark.com/tests/reactiontime - eg enda opp på 250ms reaksjonstid.