N-key rollover reports any simultaneous combination correctly; games and pro boards rely on it

What it is

N-key rollover (NKRO) means any number of keys, anywhere, held together are reported one by one, with neither ghosts nor blocked real keys. It is anti-ghosting taken to the specification ceiling, not a typing-speed spec. Two-handed chords like a music keyboard, WASD plus a row of skills, and accessibility setups that close several physical switches at once all depend on it. An office board's “anti-conflict” usually covers keys near modifiers only, not NKRO.

Why it happens

Each switch is in series with a diode, or each key has its own controller pin, so matrix sneak paths are cut and the scan can read any subset. The report path must also be wide: classic USB HID boot protocol carries six non-modifier keys (6KRO); true NKRO needs a full HID report or an NKRO-specific protocol. “Marketed as NKRO” and “still six keys in BIOS or on some hosts” can both be true. Bluetooth packets are smaller, so wireless often drops from NKRO to 6KRO. What professionals buy is this report chain, not only switch feel.

Studying it

On a board that claims NKRO, increase simultaneous keys (past ten) and check with test software whether the reported set equals the physical set. Test USB, Bluetooth, and BIOS-compatible mode separately. Contrast a membranous board with no diodes. Record game clips where more than six keys all remain live. Repeat on a host that only speaks boot protocol; advertised NKRO often falls back to six keys there. Do not use typing WPM as an NKRO metric.

Where it stops holding

Ordinary prose almost never holds ten keys; NKRO has no perceptible mail benefit. Piano-style input, fighting games, and dense flight-sim binds are where it becomes required. Some “NKRO” unlocks only with a driver and falls back to 6KRO without it, which lies at unboxing. Soft-keyboard multi-touch limits are set by the touch controller and are not NKRO. PS/2-era boards could scan true NKRO; that does not imply a modern USB plug does the same.

Applying it

• In game and peripheral recommendation lists, spell out NKRO (and USB wired mode); disclose wireless downgrade.
• Do not label 6KRO as n-key rollover.
• Select accessibility multi-switch hardware for NKRO or independent input paths.
• Verify on the target host and connector: eight unrelated keys down at once, test page shows eight downs. If one is missing, remove NKRO from that connector's claims.

Related

• Same group: C6.31.1 Holding a character key starts repeat; repeat rate and initial delay are independent parameters · C6.31.2 A repeat rate that is too fast produces extra characters when the user wanted one · C6.31.3 Fast multi-key presses on a keyboard with weak anti-ghosting drop some keys
• Adjacent: C6.20 Modifiers and key combinations · C10.01 Tactile localization of physical keys
• Search: n-key rollover · NKRO · 6KRO