Key rollover

Key rollover is the ability of a computer keyboard to correctly handle several simultaneous keystrokes, often important in gaming as well as for testing rapid key pressing and reaction time. A keyboard with n-key rollover (NKRO) (also known as full key rollover) can correctly detect input from each key on the keyboard at the same time, regardless of how many other keys are also being pressed. Keyboards that lack full rollover will register an incorrect keystroke when certain combinations of keys are pressed simultaneously. Rollover has applications for stenotype, electronic music keyboards, gaming, and touch-typing generally.

Keyboard usage

During normal typing on a conventional computer keyboard, only one key is usually pressed at any given time, then released before the next key is pressed. However, this is not always the case. When using modifier keys such as Shift or Control, the user intentionally holds the modifier key(s) while pressing and releasing another key. Rapid typists may also sometimes inadvertently press a key before releasing the previous one.

Certain unusual forms of keyboarding require multiple keys to be pressed or held down simultaneously;

for example:

Braille2000 keying requires as many as six keys to be pressed at once analogous to the six dot keys of a Braille typewriter.

Stenographic typing also requires the ability to press multiple keys at once to form "chords."

Some computer games require multiple keys (other than the usual modifier keys) to be held down while others are pressed and released, in order to perform actions simultaneously;

a common scenario would be the holding down of two Arrow keys or WASD keys in order to move the player in a diagonal direction.