Keyboard Ghosting Explained
Keyboard ghosting is when pressing several keys at once causes a key to be missed or a phantom key to register. Here is why it happens and how to test for it.
Why it happens
Keys sit on a matrix of rows and columns. Without a diode for each key, some three-key combinations become ambiguous, so the controller blocks them. Gaming keyboards add diodes for “N-key rollover”.
How to test
Open the keyboard test and hold combinations you use, such as W+A+Shift+Space. Every key should light up. USB keyboards may be limited to 6 keys in boot mode.
Keys not working at all
Clean under the keycap, try another USB port and check for a Fn-lock or Game mode that disables keys. Also see the mouse test for double-click issues.
Related tools
Frequently Asked Questions
Q.Is ghosting a hardware fault?
No, it is a design limit of the matrix.
Q.What is NKRO?
N-key rollover: every key registers independently.