Glossary
Rollover typing
Rollover, or key rollover, is the number of key presses a keyboard can detect when they overlap. Two-key rollover reliably detects only two keys at once, and a matrix keyboard without diodes can register a ghost key when three keys are pressed together.
Updated October 16, 20262 cited facts, each traced to its source
Also called key rollover, rollover.
Rollover is how many key presses a keyboard can track when they overlap. Fast typists often press the next key before the previous one is released, and the keyboard has to register both. A keyboard with limited rollover can drop or confuse those overlapping presses.
Two-key rollover detects only two keys at once
The simplest design is two-key rollover. A keyboard with "two-key rollover" can reliably detect only two keys used simultaneously 1. Holding one key and pressing a second works, but a third press while two keys are down is not reliably detected. For ordinary typing this limit is seldom noticed. It matters more for fast overlapping typing and for games, where several keys are held together.
Matrix wiring can create ghost keys
Many keyboards read their keys through a grid of rows and columns, called a matrix. This wiring keeps the circuit simple, but it creates a specific fault. Pressing as few as three keys can cause ghosting effects in a matrix keyboard without isolation diodes 2. The keyboard then reports a key that nobody pressed. Matrix layouts are chosen so that common modifier combinations avoid the fault, but other combinations can still trigger it.
Keyboards that handle more simultaneous keys are called N-key rollover, or NKRO.
What rollover means for typing and dictation
Rollover matters when you type quickly on a mechanical or gaming keyboard. A missed or phantom key shows up as a wrong letter, which costs time to fix. If you notice errors that appear only during fast bursts, check the keyboard's rollover before you blame your technique.
Dictation avoids the problem entirely, because speech does not use key presses. A dictated draft does not depend on how many keys a keyboard can track. Rollover still matters for the editing pass, when you correct the draft by keyboard. Our guide to how to type faster covers the technique side, and the question on whether mechanical keyboards make you type faster covers the hardware side.
Related terms
- Keystroke dynamics: the study of the timing between key presses.
- Typing accuracy: the share of keystrokes typed correctly.
- Keystrokes per character (KSPC): how many key presses each character takes.
- Words per minute (WPM): the unit used to report typing speed.
Guides that cover it
Evidence
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Related terms
- Typing Speed: Average WPM and How to Type FasterThe topic this term belongs to
- Articulation rateArticulation rate is the number of syllables a speaker produces per second, leaving out pauses. It measures how fast the speech itself comes out, so it is usually faster than the overall speaking rate that counts every pause.
- Characters per minute (CPM)Characters per minute (CPM) is the number of characters typed in one minute, counting spaces and punctuation. Words per minute is the same count divided by five, so a typist at 50 WPM enters 250 characters per minute.
- ColemakColemak is an alternative English keyboard layout, introduced in 2006 and designed for efficient, comfortable touch typing. Its supporters describe it as the third most popular layout for English touch typing, after QWERTY and Dvorak, but that ranking has no stated method.
- Dvorak Simplified KeyboardThe Dvorak Simplified Keyboard is an alternative English keyboard layout that places the most common letters on the home row. Dvorak and Dealey applied for a patent on it in 1932, but the studies that claimed it was faster than QWERTY have been criticized, and the evidence for a speed gain is weak.
- Home rowThe home row is the middle row of keys on a keyboard, where the fingers rest when you touch type. On a QWERTY keyboard it holds A, S, D, F for the left hand and J, K, L and semicolon for the right, and every other key is reached by moving a finger away from it and back.
- Hunt and peckHunt and peck is a typing method in which the typist finds each key by sight and presses it with one or two fingers, usually the index fingers. It is also called two-finger typing, and it differs from touch typing, which relies on memorized key positions and the home row.
- Keystroke dynamicsKeystroke dynamics is the identification of a person from the rhythm of their typing, using the timing between key presses as a pattern much like a handwritten signature. It is a behavioral biometric, so it supports identity checks through statistical matching rather than proving who typed.
- Keystrokes per character (KSPC)Keystrokes per character (KSPC) is the average number of keystrokes a text entry method needs to produce one character of text. A basic QWERTY keyboard scores 1, methods that need more presses score above 1, and word prediction can score below 1.
- Keystrokes per hour (KPH)Keystrokes per hour (KPH) is the number of key presses made in one hour. It is the standard unit for numeric data entry, where many jobs require 8,000 or 10,000 keystrokes per hour, and it counts keys rather than words.
- Oral reading fluency (ORF)Oral reading fluency (ORF) measures how many words a reader gets right in one minute of reading a passage aloud. Schools record the result as words correct per minute (WCPM), which subtracts the words read wrongly from the total.
- QWERTYQWERTY is the standard letter arrangement on English keyboards, named for the first six letters of the top row. Christopher Latham Sholes devised it in the early 1870s for typewriters, and it is still the layout most people type on, even though faster layouts have been proposed.
- StenotypeA stenotype, also called a steno machine, is a chorded keyboard that stenographers use for shorthand, pressing several keys together to produce a syllable or word. The NCRA's court reporter skills test sets a speed of 225 words per minute, and voice writing is a newer method that uses speech recognition instead.