Keyboard Ghosting vs N-Key Rollover
Why some key combinations don't register, what ghosting, blocking, 6KRO and NKRO actually mean, and how to check your own keyboard with the keyboard ghosting test.
By Ritvik Kudalkar, published . A 6 minute read.
How a Keyboard Matrix Works
A full-size keyboard has over 100 keys, but its controller doesn't have 100 input pins. Instead, keys sit at the crossing points of a grid of wires: rows and columns. The controller powers one column at a time and reads which rows respond, so it can scan every key with far fewer connections.
This works perfectly while you press one or two keys. With three keys held at three corners of a rectangle in the grid, current can flow backwards through them and make the fourth corner look pressed too, even though it isn't.
Ghosting vs Blocking
- Ghosting is when the keyboard reports that phantom fourth key. In a game, your character might suddenly move or act on its own.
- Blocking (or jamming) is how most keyboards prevent ghosting: when a combination could be ambiguous, they ignore the new key. No phantom key appears, but the key you actually pressed is lost.
Real ghosting is rare on modern keyboards. Blocking is common, and it's what players usually mean when they complain about ghosting: "I was holding W, A and Shift and couldn't jump."
What Rollover Means
Rollover is the number of keys a keyboard can register at once without blocking or ghosting.
| Term | Meaning | Typical Keyboard |
|---|---|---|
| 2KRO | Any 2 keys always register; more may block | Basic office and laptop keyboards |
| Anti-ghosting (zones) | Common gaming keys wired to avoid blocking | Budget gaming keyboards |
| 6KRO | Any 6 keys plus modifiers | Many gaming keyboards, USB boot mode |
| NKRO | Every key, in any combination | Mechanical and enthusiast keyboards |
How Keyboards Achieve N-Key Rollover
To avoid ghosting completely, each key needs a small diode that stops current flowing backwards through the matrix. With a diode on every switch, the controller can always tell exactly which keys are down. Most mechanical keyboards are built this way. Cheaper membrane keyboards skip the diodes and rely on careful matrix layout, putting common gaming keys on separate rows and columns so they rarely collide.
Even with diodes, the keyboard must report every key to the computer. The basic USB keyboard format, used by BIOS screens and many older systems, carries only six normal keys plus modifiers. So many NKRO keyboards default to 6KRO and offer NKRO as an option.
How to Test Your Keyboard
- Open the keyboard ghosting test and click the on-screen keyboard.
- Hold the keys you use together in games, adding one at a time.
- If a key you hold doesn't light up, that combination blocks. If an unpressed key lights up, that's ghosting.
- Check the combos list and the Max at once count for your keyboard's rollover.
What to Do if Your Keyboard Blocks
- Turn on NKRO in the keyboard software, if available.
- Rebind the action that gets blocked to a key that works with the rest of your combination.
- Connect directly to the computer rather than through a hub or KVM switch.
- When buying, look for "N-key rollover" or "full anti-ghosting", not just "anti-ghosting keys".