Rollover classes at a glance
| Class | Simultaneous normal keys | Modifiers extra? | Typically found on |
|---|---|---|---|
| 2KRO | 2 guaranteed; a 3rd key works only in some combinations | Yes | Budget membrane boards, many older laptops |
| 6KRO | 6 | Yes (separate bitmask) | Standard USB keyboards; "BIOS mode" of gaming boards |
| NKRO | Every key independently | Included | Mechanical/gaming boards, mostly in wired mode |
Two caveats worth knowing. First, a board can be better than 2KRO in most areas and still block specific three-key clusters — the limit is per matrix region, not global. Second, anything between your keyboard and the browser can lower the score: KVM switches, some USB hubs, remote-desktop sessions and Bluetooth power-saving modes are the usual suspects.
Ghosting vs blocking, in one paragraph
Inside a cheap keyboard, keys sit on a grid of row and column wires. Press three keys that form three corners of a rectangle on that grid and the controller cannot tell whether the fourth corner is also pressed — a phantom, "ghost" key. Because typing a letter you never pressed is the worst possible failure, controllers block instead: they simply ignore the third key of a dangerous trio. So what users experience as "ghosting" in games is nearly always blocking — a missing keystroke, not an extra one. Boards with a diode behind every switch (true NKRO designs) have no ambiguous rectangles and never need to block.
Worked example: proving a 6KRO limit
Hold W + A + S + D — the counter reads 4. Add Space: 5. Add K: 6. Now press J while everything stays down: the held count stays 6 and J never lights. Release K, and J suddenly registers. That clean "one in, one out" behaviour at exactly six keys is the USB boot-protocol limit — working as designed, not a defect. Repeat the run holding Shift and Ctrl too: the counter reaches 8 (6 letters + 2 modifiers), confirming modifiers ride in their own lane.
Worked example: catching real blocking
On one budget membrane board, holding Q + W registers 2, but adding E shows nothing — count stuck at 2 — while the combination Q + P + M happily reaches 3. Same board, same three fingers, different result: that is a matrix cluster limit. The practical consequence for a gamer: if your crouch key shares a cluster with your movement keys, remapping crouch one key sideways can fix "my keyboard eats inputs" for free, no new hardware needed.
How to run a fair test
- Use the wired connection and a direct USB port for the baseline (no hub, no KVM).
- Build combos from real usage: your movement cluster + jump + ability keys, or both players' zones on a shared board.
- Try clustered keys (WASD region) and spread keys (opposite board corners) — matrix limits show up in clusters.
- If the number looks low, check for a mode toggle (many boards ship in 6KRO for BIOS compatibility) and retest.
- Retest over Bluetooth if you use it — expect the wireless number to be the one you live with.
Missing keystrokes that appear only when typing fast — rather than when holding keys — are usually not a rollover problem at all. Check for double or dropped registrations with the keyboard chatter test, and run the full keyboard tester to make sure every individual key is alive. Laptop matrices carry their own quirks, covered in the laptop keyboard test.