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Keyboard glossary


General list of terms

Abbreviation of 1 Form A; alternative term for Single Pole Single Throw Normally Open (SPST-NO)
Abbreviation of 1 Form B; alternative term for Single Pole Single Throw Normally Closed (SPST-NC)
Abbreviation of 2 Form A; alternative term for Double Pole Single Throw Normally Open (DPST-NO)
(On PCBs from Alps USA and Hi-Tek) Artwork (confirmed from a keyboard where it was written out in full)
Alternate action
An alternate action switch alternates between open (off) and closed (on) each time it is pressed. Typically, the plunger will sit lower when the switch is closed, and will return to its original position when released, but Clare-Pendar for one differentiate between alternate action (which simply changes state) and latching (where the plunger is held in a lower position when the switch is closed). Other terms for such switches are latching, locking and push-push.
Bar mount
See under straight mount
Micro Switch’s term for double action
Coding keyboard
See under encoding switch
Coding switch
See under encoding switch
See under keyboard controller
See under membrane
Double action
See double action.
Double depression
The term used by Licon for double action
Double Pole Double Throw
Double Pole Single Throw
Dual mode
Each key produces two separate outputs, e.g. ASCII with uppercase and lowercase, numbers and symbols; see also modes, mono mode, tri-mode, quad mode
See under keyboard encoder
Encoding switch
Also known as a coding switch, this is a keyswitch with the ability to encode its own output without the need for a diode matrix or encoding logic. Such switches were complicated, and their use seems to have been fairly short-lived. See under encoding and output for details.
Flexible printed circuit
A printed circuit that uses a flexible sheet of plastic (generally polyester) instead of a rigid board, which can be found in membrane keyboards; the circuit tracks are generally described as being a silver–carbon ink
Form A
Single Pole Single Throw Normally Open (also written 1A, especially by Cherry) or simply Normally Open
Form B
Single Pole Single Throw Normally Closed (also written 1B, especially by Cherry) or simply Normally Closed
See under flexible printed circuit, above
Full travel
Not clearly defined; see under travel
After actuation, the switch must be released a short distance to release; see under travel
Intelligent keyboard
A historic term to refer to a keyboard that uses microcontroller-based matrix encoding
Keyboard controller
A microcontroller used as a keyboard encoder, with the encoder firmware stored in mask ROM, PROM/EPROM or internal flash memory; see under intelligent keyboard and contrast with keyboard encoder
Keyboard encoder
A single-chip keyboard encoder logic circuit that combines all the separate TTL components required for encoding, which is not to be confused with a microprocessor-based keyboard controller; see LSI-based matrix encoding
This is the removable portion of a key that contains the legend. Traditionally it has been attached to the keyswitch by way of a friction fit, but other methods of attachment exist, especially with ultra-low-profile keyboards such as those found on notebook computers.
Another term for keycap
See under plunger below; on this site, “keystem” is used to mean the vertical post on the plunger that holds the keycap via a friction fit
Some form of (normally electrical) means of detecting that a key has been pressed. Typically this term refers to a discrete pushbutton switch, rather than to a single station from a single assembly (such as screen-printed flexible printed circuits). In many cases, the switching is entirely solid state, using for example magnetic field or light detection rather than switch contacts. Keyboard switches have specific characteristics over ordinary pushbutton switches that make them suitable for keyboard use. See keyboard switches and switch types for more details.
See under alternate action, above
The writing or symbol present on a key to indicate the purpose of the key, e.g. “Q” or “Insert”; the legend may be placed adjacent to the key, with the keycap itself left blank. Notably, the space bar on full size keyboards is generally left unlabelled, with the legend “SPACE” being reserved only for keyboards where the space bar is so small or so far from its normal position that it is not obvious to the operator which key it is. The legend may be engraved, screen or pad printed, dye sublimated, written with a laser, or moulded directly into the keycap.
Depending on the era, possibly any conductive switch, or a switch with hard metal contacts, operated through physical engagement (rather than by a magnet, as in reed switches); see mechanical under switch types
A thin, flexible layer of material; in membrane keyboards this refers to the layers of plastic (typically Mylar polyester) used for the flexible printed circuits and the intermediate spacer layer (Datanetics used the term “diaphragm” for their flexible printed circuits, and in DC-50 switches, for the outer layers of plastic)
For keyboards that emit ASCII or EBCDIC character codes directly, and similar arrangements, this is the number of separate output codes that each key can produce depending on modifier key usage; where the keyboard protocol provides scancodes only, the interpretation of the modifier keys is left entirely to the host operating system just as are the outputs of all the normal keys; see also mono mode, dual mode, tri-mode, quad mode
Mono mode
Each key produces only one output; see also modes, dual mode, tri-mode, quad mode
a) In modern usage, a switch that is actuated only when the plunger is held down; b) historically, a switch that actuates for a brief instant as the plunger is depressed, releasing automatically immediately afterwards and remaining released until the plunger is released
N-key rollover
The modern definition of N-key rollover is ability to detect an unlimited number of simultaneous keypresses, but other definitions have been encountered
Normally Closed
Normally Open
Further travel after actuation; see under travel
A keystroke sensing arrangement that uses light beams to detect when a key is pressed and, in photoelectric encoder keyboards, the identity of the key that was pressed. See photoelectric under switch types for more details.
The component of a switch that moves up and down when you press a key
The distance a switch can be pressed up to the point that it actuates; see under travel
See under alternate action, above
(On PCBs from Alps USA and Hi-Tek) Likely “Printed Wiring Board”, an alternative term for printed circuit board (PCB)
Quad mode
Each key emits one of four different outputs depending on modifier key usage; see also modes, mono mode, dual mode, tri-mode
Reed switch
The term “reed switch” primarily refers to a hermetically sealed glass tube containing magnetically-operated switch contacts. Such a device has no other parts: all other components (including even the magnet) are extra. The term “reed switch” can also be used to refer to a complete self-contained pushbutton switch (complete with plunger, return spring and magnet) that contains a reed capsule: see reed switch under switch types.
Secretarial shift
Secretarial shift is a shift lock system that mimics the behaviour of shift lock on a manual typewriter.
Secretary shift
A variant term for secretarial shift.
An alternative term for plunger; this term would have been better applied to switches with internal horizontal sliding components (in particular Sasse Series 25 and Alps SKFL Lock)
Solid state
Non-contact switching (e.g. Hall effect, magnetic valve, foam and foil); see switch types
Single Pole Double Throw
Single Pole Single Throw
Possibly short for “keystem”; see under plunger below.
Straight mount
A thin, oblong keystem; this has also been referred to as “bar mount”, which helps differentiate between “straight” being used to indicate that the keystem vertical angle is 0° (upright)
A connection on a keyboard PCB that indicates when an output code (such as a scancode or ASCII code) is ready to be read from the data lines. The strobe signal may be repeated if auto-repeat is triggered (such as by a double-action switch or by holding the Repeat key), and it may be delayed to ensure that the data signal is valid before it is read.
Asian abbreviation for “switch” (used by Tai-Hao and Sejin).
The vertical motion of the switch; see under travel
Each key produces one of three different outputs depending on which if any of two different modifier keys is held; for an ASCII keyboard, control codes are emitted if the control key is held, and uppercase letters and symbols are emitted if the shift key is held (this differs from a scancode-based keyboard that emits the scancode of each key regardless of modifier key state, such as XT and AT protocol keyboards); see also modes, mono mode, dual mode, quad mode



The component of a pushbutton switch that provides the vertical motion is most commonly termed the “plunger”. The part of the key that you see—with the inscription that tells you what the key does, such as “Q” or “Shift”—is called the “keycap” or “keytop” (or sometimes translated as switch hat). The keycap is generally a separate part that attaches onto the plunger of the switch. The keycap is normally a press fit (friction fit), into a slot or onto a post on the plunger, but it may also clip on.

The plunger may also be called a “keystem” (including in historical patents), and particularly with Cherry MX switches this is shortened to simply “stem”. This is confusing, as “stem” implies a narrow object; it may be that the post that holds the keycap has become a metonym for the entire plunger.

Another widely-used term in keyboard enthusiast community is “slider”. This is rarely seen in official literature, but the cross-section diagram in the datasheet for Fujitsu FKB4690 Series spring-over-membrane keyboards refers to the plunger as “スライダー”: “slider” (phonetically, “suraidā”). “Slider” could be a Japanese term, which may explain why Alps SKCL/SKCM plungers are most commonly associated with the term “slider”, while German Cherry switches have “stems”. US patent 4529849 from Fujitsu (filed in 1983) uses “slider” in English, while US patent 4642433 for Alps SKCM uses “stem”.

Within this site, the moving part is referred to as a “plunger” to best accommodate standard English-language terminology, although older pages will still say “slider”. The term “keystem” is adopted here to refer specifically to the projection on the plunger that holds the keycap. Where the plunger is slot-mount, the keycap has the stem instead.