NKRO, 6KRO, ghosting, and blocked keys explained

Rollover terminology describes what happens when multiple keys are held, but several different behaviors are often called “ghosting.” Separating them makes a test much easier to interpret.

Rollover is a simultaneous-input limit

Key rollover is the number or pattern of held keys a keyboard can report correctly. A 6KRO keyboard generally reports six ordinary keys at once, often with modifiers handled separately. NKRO means the design intends to report every supported key independently, although connection mode, firmware, and implementation still matter.

A rollover rating does not promise that every application accepts unlimited inputs. The operating system, browser, and application also process the reports.

Ghosting and blocking are different

In a simple keyboard matrix, certain three-key combinations can make an unpressed intersection look electrically possible. A true ghost is an extra key report that the user did not press.

Many keyboards prevent that false report by blocking one of the ambiguous real keys. The safer outcome is a missing key rather than an invented one. Users often call both results ghosting, but they point to different behavior:

Observation	Meaning
A pressed key is absent	Blocking or rollover limitation may be involved
An unpressed key appears	A ghost or another unexpected input was reported
A key works alone but not in one chord	The combination matters more than the individual switch

Test the combinations you actually use

Use the keyboard rollover tester and hold a known chord slowly. Gaming examples might combine movement keys, sprint, crouch, and a number key. Editing and accessibility workflows may rely on several modifiers plus another key.

Watch the held-key count and event history. Add one key at a time so you know exactly which addition changes the result. Then release the chord and repeat it in a different order. Matrix-dependent blocking can vary with the set of positions, while application shortcuts may vary with press order.

Interpret browser evidence carefully

The page can display only events delivered by the browser. If an operating-system shortcut takes over, the missing browser event does not prove the keyboard failed. Likewise, a virtual key remaining highlighted after the window loses focus can reflect a missing release event, which is why a good tester clears transient held state on blur.

Repeat a failing chord in another browser and on another computer. Also compare USB and wireless modes if the keyboard supports both, because firmware may expose different report formats.

NKRO is useful when your real combinations exceed a lower limit, but a label alone is not the test. Verify the exact chords needed for your games, creative software, assistive controls, or work shortcuts. A keyboard that reliably reports those combinations meets the practical requirement even if the marketing term is less dramatic.

Why nearby keys can behave differently

Keyboard matrices arrange switches into electrical rows and columns. Two chords with the same number of held keys may use different matrix paths, so one can work while another blocks. This is why a single impressive ten-key demonstration does not prove every five-key gaming chord.

Manufacturers can add diodes or design matrix wiring to prevent ambiguity, but product layouts and firmware vary. Modifiers may also be transported differently from ordinary keys. Treat “6KRO” as a broad capability description and test the positions that matter.

Connection mode can change the available report format. A keyboard may expose NKRO over wired USB but use a smaller report in a compatibility or wireless mode. Console, KVM, BIOS, and older operating-system environments may prefer a conservative mode. Check the manual before interpreting different results as a defect.

Build a useful combination matrix

Create a short list of workflows and test each one several times:

Workflow	Example chord	What to watch
Movement	W + A + Shift + Space	Every held key remains visible
Editing	Ctrl + Shift + arrow	Shortcut key arrives with both modifiers
Music	Several mapped note keys	No blocked note or unintended extra note
Accessibility	Multiple modifiers + command	Required sequence remains reliable

Add keys slowly, photograph or record the held set, and repeat in another order. If an unpressed key appears, stop and reproduce the smallest combination that creates it. If a pressed key disappears, remove one held key at a time to identify the blocking set.

This minimal failing combination is far more useful than a maximum-count score. It can be compared across connection modes, firmware versions, and devices, and it gives support teams a precise case to reproduce.

Technical references

• The USB-IF HID Class specification documents the six non-modifier-key limit of the boot-keyboard protocol.
• The W3C KeyboardEvent code Values recommendation defines the physical key-position codes a browser can expose.