Blur Busters Forums

I know that PS/2 has a lower input lag than USB, but if I have a mechanical USB keyboard, will I get the benefit of lower input lag if I simply use a PS/2 adapter?

Yes and the difference is so tiny that hardly can be noticed.

imo main advantage of ps2 is full nkro

Most keyboards don't work with a PS/2 adapter. The adapter only works with keyboards that actually support PS/2. Many USB keyboards these days have dropped PS/2 support and won't work with an adapter. Keyboards that do work with PS/2 usually state that clearly in their spec and in most cases already ship with a USB-to-PS/2 adapter included.

Also, you won't get n-key rollover just by connecting to PS/2. The keyboard itself must support this feature. PS/2 merely allows this, it doesn't guarantee it. My keyboard is a pure PS/2 one that doesn't support USB at all (I bought it in 2001, 13 years ago) and it can't handle more than three simultaneous key presses.

And last but not least, the difference in input lag between 1000Hz USB gaming keyboards and PS/2 is virtually non-existent.

from Esreality - http://www.esreality.com/post/2379352/r ... pid2321360

What is the polling rate of USB keyboards? As USB mice go up to 1000Hz, they should in theory be more responsive than PS/2 mice at 200Hz, but I never see people talk about this when it comes to keyboards.

probably 125hz

I've studied the USB HID specification, and it turns out that the polling rate is set by a byte in the device ROM. A USB 1.0 frame is 1ms, hence the max of 1000Hz for gaming mice. Most mice I tested had bytes set to something higher, correlating with microseconds, but interestingly, a mouse was set to 10ms, but it updated as if it were set to 8ms. Probably rounding by Windows. I checked my keyboard, and I was pleasantly surprised when I saw that it was set to 1ms.
Still, might as well use PS/2 just to save some CPU cycles.

I've casually made some USB HID devices *using low-speed USB mode* (using V-USB) and found that the OS generally limits the polling rate for HID devices to 8ms (125Hz), even if the device specifies less. It also polls it at 8ms even if the device specifies 10ms. Linux (and Windows and possibly OS X I've read) can be told to ignore this and poll at 1ms (1000Hz), which tends to work for many things.

EDIT: the above applies only to low-speed USB devices. I've found that others aren't affected and work at whatever polling rate the device requests.

Are you sure? Because my G400 reports at 1000Hz without installing any drivers.