Do USB or PS/2 keyboards respond faster?

There was a study in 2002 that evaluated the response times of various keyboards so that those delays could be better accounted for in experiments where subjects' response times were being measured with keyboards.

There are a number of interesting results, but the point relevant to this question is that there was a fairly significant variance between keyboards, and all the USB keyboards tested had a longer effective scan interval (18.77 ms - 32.75 ms) than the PS/2 keyboards (2.83 ms - 10.88 ms).

To explain it simply, keyboards scan across each column of keys and check to see whether any are pressed. So your signal isn't generated the instant you press the key, but rather when the controller scans the key and sees that it is pressed. After the keyboard sends the PC the signal there are obviously additional delays before the character appears on your screen, but those are fixed regardless of the keyboard type.

So if you pressed a key the moment after it was scanned, it could take almost 30ms longer on a slow USB keyboard to be detected and sent to the computer. I'm sure there are some serious gamers who would claim to notice that kind of delay.

I didn't see it mentioned anywhere on here, and although old, this post is still returned via a simple Google search -- so not only is the response time faster but PS/2 keyboards support unlimited roll-over, meaning you can press as many keys as you wish at once and they will all register. USB maxes out at 6, I believe. As a programmer, I don't often run into this issue, but for gamers, this means everything!

Any PC user with knowledge knows that PS/2 is a much better connection than USB. First,it will give you total freedom with no limit to the amount of simultaneous key presses. And, equally as important, using the PS/2 may just improve your overall gaming experience. The reason is that when you use a USB keyboard your computer is actually using CPU time polling your keyboard. The higher the polling rate the more CPU time is used to perform the polling. And because of the built-in debounce rate found on any quality keyboard, any polling rate above 200Hz is simply a waste of CPU time and really just a result of pointless marketing hype. Unlike USB keyboards a PS/2 keyboard isn’t polled at all. The keyboard simply sends a signal to the computer as key presses are made, which causes a hardware interrupt, forcing the CPU to register the signal.