QuickDeviceTest Device test / Ghosting test
Keyboard ghosting test
Hold down the key combinations you really use and see whether every key registers. The rollover counter tells you how many keys your keyboard reports at once.
Hold down as many keys as you can at once (try A S D F J K L ; or Q W E R T). The max rollover counter shows how many your keyboard reports together. If it stops at 6, you have a 6-key-rollover USB keyboard; if some combinations stop at 2 or 3, those keys ghost-block each other.
Combinations worth testing
| Use | Hold together |
|---|---|
| FPS movement + jump + sprint | W A Shift Space |
| Strafe + crouch + reload | A D Ctrl R |
| Two players, one keyboard | W A S D + ↑ ← ↓ → |
| Home row stress | A S D F J K L ; |
What the number tells you
If the max rollover stops at 2 or 3 for some combinations but goes higher for others, your keyboard has a matrix without diodes and blocks particular key groups. If it always stops at 6 (plus Ctrl, Shift, Alt, Win), it is a standard 6-key-rollover USB keyboard. If it keeps climbing past 10, it supports N-key rollover.
One caveat we can't get around: some laptops and operating systems limit rollover further, and a few keyboards switch to 6KRO over Bluetooth. Test in the connection mode you play in.
Why keys ghost: the wiring matrix
A keyboard doesn't give each key its own wire. Keys sit where row wires cross column wires, and the controller scans one row at a time, checking which columns light up. Press three keys that form three corners of a rectangle and electricity can sneak backwards through them, so the fourth corner looks pressed too. Tap keys below (or press the demo).
Rows are Q-W-E, A-S-D, Z-X-C; columns are Q-A-Z, W-S-X, E-D-C. Try any three corners of a rectangle.
Questions
What is keyboard ghosting?
When you press certain combinations of keys, a basic keyboard either registers a key you did not press (a ghost) or, more commonly, blocks one of the keys so it does not register at all. It comes from how keys share row and column wires.
How do I test for ghosting?
Hold down the key combinations you actually use, such as W+A+Shift+Space for a game, and watch whether each key lights up and the rollover count rises with every key. If a key you are holding stays dark, it is being blocked.
What is the difference between 6KRO and NKRO?
6KRO means the keyboard can report six ordinary keys plus modifiers at once, which is the limit of the standard USB boot protocol. NKRO (N-key rollover) means every key can be reported at the same time, usually through a different USB report format.
Does ghosting matter for typing?
Rarely. Fast typists overlap only two or three keys. It matters for games and chorded shortcuts where you hold several keys at once.
Can I fix ghosting?
Not in software. Some keyboards have an NKRO mode toggled with a key combination (see the manual) or a USB vs Bluetooth difference. Otherwise, remap game controls to keys that do not block each other, or use a keyboard with a diode per switch.