n-key rollover
Certain high-end keyboards have "
n-key rollover". This means that each key is scanned completely independently by the keyboard hardware, so that each keypress is correctly detected regardless of how many other keys are being pressed or held down at the time.
[3]
Most music keyboards use isolation diodes in their
keyboard matrix to implement full
n-key rollover (sometimes abbreviated NKRO), making them immune to both key ghosting and key jamming.
[4]
However, to reduce cost and design complexity, most computer keyboards do not isolate all keys in this way. Instead, they use a matrix of key switches, without any isolation diodes, that assumes that only a limited number of keys will be held down at any given time. With these keyboards, pressing as few as three keys can cause ghosting effects,
[4] although care is taken when laying out the matrix arrangement that this does not happen for common modifier key combinations.