Windows 7 – Multiple keyboards

Response Times PS/2 vs. USB 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).

More information from this Super User question itself: Do USB or PS/2 keyboards respond faster?

Power Consumption between the two devices and overall Power Consumption: (Referencing HP documentation)

• USB
  Operating voltage: + 5VDC ± 5%
  Power consumption: 50 mA maximum (with three LEDs ON)

• PS/2
  Operating voltage: + 5 VDC ± 5% Power consumption: 50 mA maximum (with three LEDs ON)

My take on it:

So the maximum possible power consumption will be +5 V and the motherboard must have accounted for this power for the PS/2 port irrespective of its actual consumption. And we know the USB does give us +5 V of power output on it. The actual power consumption varies a little from brand to brand. Some say it consumes 50 mA, and some say it's 70 mA, with a roof of 100 mA.

Nothing I have read so far says or show more than 100 mA of actual consumption. In fact, Windows also reports 70 mA of actual power required. But my MacBook shows a requirement of 100 mA on the USB. So the USB keyboard actual power consumption could be a little higher that the PS/2 keyboard. I am attaching a couple of images below.

On Windows

On MacBook

Explaining the updated question in #2:

• Well, there is only one USB controller, but every USB port is interfaced individually. So the protocol makes the device exclusive for every port.

• Every USB device connected to a port is interfaced individually. When a device is connected to the port, the port tells us which device is connected. This is like having a dedicated port per device, and the controller has the bus capabilities of sending multiple requests simultaneously to the processor.

• In my reckoning, the amount of power / CPU time taken by the PS/2 or USB keyboard would be same. And if the USB keyboard was heavy on processing and power, people would have not used them inter-changeably. And we would have also read a lot more tech articles on them!

• My personal argument on this would be that Apple just gives you USB ports on the Mac Minis and iMacs, so would Apple do it if it was so power and process intensive? Even most of the new Dell machines don't have PS/2 ports on them (leave all the assembled and custom hardware aside).

As explained in an answer to your other question, the extra devices are normal.

As for your question, there's a answer here (by William.Wade.II) suggesting that the HID service may not be running. Open the control panel, Administrative Tools, Services and look for Human Interface Device Access. If not running, click "start" and see if that makes the buttons start working. If it does, right click the list item and click properties, and change startup type to automatic.

However, it is likely that you haven't installed the drivers for the keyboard. If you haven't, then do so.