Keyboard Rollover Test
Flashing means a new key signal was received. No flash means hardware non-response.
What is Key Ghosting and Rollover?
In intense gaming, you press a skill key but nothing happens? This might be keyboard ghosting or rollover limitations.
NKRO (Full N-Key Rollover)
N-Key Rollover means the keyboard can correctly identify and register ALL keys pressed simultaneously, with no limit. This is standard for high-end mechanical keyboards and essential for rhythm games and split-screen multiplayer.
Ghosting
On cheap membrane keyboards, pressing certain key combinations (usually 3 adjacent keys) may incorrectly register a 4th unpressed key - this is called 'ghosting'. To prevent ghosting, manufacturers deliberately 'block' the 3rd key's signal, causing key failures.
NKRO Technical Deep Dive
Why couldn't older keyboards achieve full N-key rollover? It's related to USB protocol limitations.
6KRO Limitation
The standard USB HID protocol specifies 8 bytes for keyboard data packets, with only 6 bytes for regular key codes. Therefore, traditional USB keyboards could only transmit 6 keys simultaneously.
NKRO Implementation
Modern keyboards bypass the 6-key limit by modifying the USB Report Descriptor or emulating multiple virtual keyboard devices, achieving full N-key rollover.
Gaming Scenarios
In rhythm games like DJMax or O2Jam, players often need to press 7-8 or more keys simultaneously. NKRO is essential here; otherwise, severe disconnects (Miss) will occur.
How to Quickly Test Rollover Capability?
Press and hold both left and right Shift keys simultaneously.
While holding Shift, use your palm to press as many letter keys as possible.
• Stuck at 6: Standard 6KRO keyboard.
• Over 20+: True NKRO keyboard.
• Only 3-4: Low-end membrane keyboard with severe conflicts.
FAQ
Q.Does Mac support NKRO?
MacOS NKRO support depends on keyboard firmware. Many keyboards claiming NKRO only achieve 6KRO on Mac, because macOS has stricter parsing of non-standard USB HID protocols.
Q.Why does my mechanical keyboard only have 6KRO?
For maximum compatibility (especially in BIOS), many mechanical keyboards ship with 6KRO by default. Check your manual - there's usually a hotkey (like Fn+N or Fn+PrtSc) to switch to NKRO mode.
Q.Is PS/2 interface better?
For rollover, the old PS/2 interface does have natural advantages - it natively supports full NKRO and has no polling delay (interrupt-based). But as it doesn't support hot-plugging and the port is obsolete, it only exists on vintage equipment.