n-key rollover

A computer keyboard circuit that allows any number of keys to be pressed in succession without having to lift a finger from any of the previous keys. Only a small number of high-end keyboards have n-key rollover. Most have 3-key rollover, which is essential for touch typing. The Braille2000 application requires 6-key rollover for entering Braille because as many as six keys may be depressed at one time.

Test the Rollover
To test the rollover, press as many keys as you can on at least two different rows simultaneously. If they all display on screen, the keyboard has sufficient rollover for that number of keys. It is difficult to test n-key rollover with two hands. It requires the use of a ruler or edge of a book to depress that many keys.