Understanding Rollover

The proper use of these tests to determine keyboard rollover is to discover the smallest number of keys that can always be recognized.

Example 1

  • You press q (pause) w (pause) e (pause) r (pause) t (pause) y, one at a time, and all five keys are recognized.
  • You press q (pause) w (pause) a (pause) s (pause) z (pause) x, one at a time, and qw are recognized but a is not recognized (even if s, z, and x are recognized).

Example 2

  • No matter which keys you press, the first 6 keys are always recognized.
  • The seventh key, no matter what it is, is never recognized.
This is 2-key rollover.This is 6-key rollover.

Modifier keys such as shift and control are NOT included in the rollover number.

The USB HID keyboard driver is limited to 6-key rollover per device. PS/2 has no such limitation. Some USB keyboards are comprised of more than one logical USB device, for example in order to get 12-key rollover.

test 1: xem

Directions: Type some keys.

Keys accepted:

Test 1 was originally found at