Me­chan­i­cal key­board jar­gon ex­plained

HWM (Singapore) - - Features And Performance -

With terms like N-key rollover, ac­tu­a­tion, re­set point and anti-ghost­ing tech­nol­ogy, pick­ing the right me­chan­i­cal key­board can get con­fus­ing. Here’s what ev­ery­thing means.

Ac­tu­a­tion Point

The point at which key in­put is reg­is­tered, on all Cherry MX switches, this point is half­way down the switch.

Re­set Point

The point at which the key re­sets and can be pressed again. Black and Red switches have match­ing ac­tu­a­tion and re­set points, mak­ing them the best for dou­ble-tap­ping. On Brown switches, the points are about 0.1mm apart, while Blue switches have a re­set point about 0.75mm higher than the ac­tu­a­tion point.

Lin­ear Vs Tac­tile

Lin­ear switches of­fer the same feel all the way through the key press, re­sult­ing in a smoother feel. Tac­tile switches have a no­tice­able bump half­way through to let you know you’ve ac­ti­vated the switch.

Key Rollover

Key rollover refers to how many si­mul­ta­ne­ous key presses can be suc­cess­fully pro­cessed. Only PS/2 key­boards are ca­pa­ble of true N-key rollover i.e. ev­ery key can be pressed si­mul­ta­ne­ously. This is be­cause these key­boards are di­rect in­put, with each key­stroke regis­ter­ing straight to the CPU. USB key­boards, on the other hand, are limited by the buf­fer size of the USB con­troller to just 6-key rollover, or up to 10-key when in­clud­ing mod­i­fiers. How­ever, many com­pa­nies have found ways to in­crease key rollover via USB. For ex­am­ple, by hav­ing the com­puter reg­is­ter mul­ti­ple (some­times as many as six) key­boards on the USB con­troller, en­sur­ing mul­ti­ple in­puts are sent through si­mul­ta­ne­ously.

Polling

Polling refers to how of­ten the CPU re­ceives in­put from the key­board. The higher the num­ber, the more fre­quently in­for­ma­tion is sent. Only USB key­boards re­quire polling (as PS/2 key­boards are di­rect in­put). Re­al­is­ti­cally, any­thing over 200Hz is un­nec­es­sary as in­put from a key­board is limited by the time it takes for a key to re­set.

Anti-ghost­ing

Orig­i­nally, ghost­ing re­ferred to a phe­nom­e­non where cer­tain com­bi­na­tions of si­mul­ta­ne­ous key presses could re­sult in ad­di­tional ‘ghost’ in­puts be­ing reg­is­tered. With mod­ern key­boards, this rarely (if ever) hap­pens any­more, and now, anti-ghost­ing gen­er­ally refers to tech­nol­ogy used to pre­vent dropped in­puts from oc­cur­ring on key­boards without full N-key rollover.

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