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Do USB or PS/2 keyboards respond faster in terms of end-to-end input latency, keystrike to character appearing on the screen?

Related:

Under either connection, is the time between keystrike to character appearing long enough to be perceptible?

Under either connection, is it possible to strike two keys in succession faster than the single-key input lag?

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I doubt the difference is noticeable, but good question, I'd like to see the answers. +1 –  Sasha Chedygov Aug 1 '09 at 20:18
    
I'd have thought that if you're going to measure from key stroke to character on screen, the overall performance of your operating system, particularly the video drivers, would have much more impact than the speed of the keyboard. –  mauvedeity Sep 29 '11 at 14:16
    
You might have a point. But if you keep the same video drivers, the USB-vs-PS/2 keyboard difference might have an impact, and can be measured. –  Torben Gundtofte-Bruun Sep 29 '11 at 15:26
    
Indeed it might, and I suppose that the gaming keyboard below would be worthwhile in that sense. But I can't really see how that kind of tiny difference would be significant most of the time. –  mauvedeity Sep 29 '11 at 15:34
    
Either way, humans cant type fast enough for it to make a difference. Use a stopwatch or stopwatch app and try to start and stop it in less than 1/10 a second and see how you do. –  Keltari Oct 11 '13 at 3:08
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3 Answers

up vote 19 down vote accepted

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.

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Very cool answer. But there is a catch: The author used DOS 6 as his operating system back then. I wonder whether the OS has some influence here or not. –  innaM Aug 1 '09 at 21:20
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Yeah that's an important point, this is pretty old hardware running on DOS. And even in this controlled environment there's a lot of variance. From the article: "The reason for our using MS-DOS was to enable us to measure time accurately, which is more difficult in a multitask ing OS, such as Win dows, Linux, MacOS, or Unix. With a multitasking OS, it takes time for the computer resources to be switched from one task to an- other, and so there is no guarantee that the resources will be available exactly when needed." –  jtb Aug 1 '09 at 21:29
    
Thanks for the great answer, and the link. –  Aidan Ryan Aug 3 '09 at 11:02
    
+1 Awesome answer. NOW I understand why my new USB keyboard is driving me nuts! –  Torben Gundtofte-Bruun Oct 9 '09 at 7:11
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@TorbenGundtofte-Bruun: We always look for an explanation of every perceived issue, whether the issue exists only our perception or in actual reality has no bearing on this fact of human nature. Most reseach I could find seem to indicate a minimum threshhold of human perception to be along the lines of 50ms or more, which is much, much higher than the difference in scanning delays between USB and PS-2 keyboards. You many indeed be a super-perceptor who is capable. But if I were you, I'd begin by changing easy things like key construction before trying to get a modern computer to support PS2. –  music2myear Sep 29 '11 at 14:52
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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!

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Apparently, PS/2 is faster. If you buy a $150 keyboard like this one designed for professional gamers, the standard interface is PS/2. It has some super fancy, gold-plated, buffered PS/2 technology, although a USB-to-adapter is included.

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evidence? otherwise this is just conjecture –  Keltari Oct 11 '13 at 3:05
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