Switch terminology
When discussing keyboard switches, it is useful to be aware of certain terminology commonly used to describe their behavior and properties.
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Mechanical keyswitch
A name applied to high quality key switches of various types. Sometimes formalized as a switching mechanism that makes use of some sort of metal spring, this definition is somewhat meaningless given the huge variation in quality across different switch designs that have metal springs in them.
Traditionally, mechanical computer keyboards referred to the typewriter-based keyboards used quite commonly on computer consoles in the 1950s and 1960s, where the process of determining which key had been pressed was almost entirely electromechanical. In the 1970s, these were replaced with "Electronic" keyboards, which were keyboards that used digital circuitry to determine which keys had been pressed. However, as rubber dome keyboards become ubiquitous in the 1990s, companies began to market their microswitch-based keyboards as having 'mechanical' switches.
Force graph
A force graph is a graph showing the distance of key travel on the y-axis (measured in millimetres or fractions of an inch) against the force required to depress the switch on the x-axis (measured in grams or centinewtons). The force graph shows the force being exerted at any given point in the switch travel, and is useful for evaluating certain properties of a switch design, such as the amount of tactility or the location of the actuation point in the travel.
Key travel
This is the distance between the keys resting position, and its position when its been pressed down fully. So-called "Full-travel keyboards" (such as standard rubber domes and most mechanical switch designs) have a travel of about 3.5–4 mm. Short travel keyboards, like laptop ones, have a travel of about 2–2.5 mm.
Pretravel
Some switch manufacturers use the term "pretravel" to refer to the actuation distance of a switch. Pretravel is typically around half travel.
Actuation and reset points
The actuation point in a keyboard switch is the point at which the contact mechanism registers a key press. Similarly, the reset point is when the mechanism ceases to register the key press. In some descriptions, the actuation point may be referred to as the "make" or "operating" point. The reset point may also be referred to as the "break" point.
Hysteresis
In many switch designs, the actuation and reset point do not occur at the same place in the key travel - commonly the reset point will occur higher up in travel than the actuation point did. The gap between these points is referred to as the hysteresis.
The hysteresis of the blue Cherry MX switch is quite pronounced due to its design, and this means it becomes harder to rapidly press a key multiple times in a row ('double tap'). This makes it less suitable for playing certain types of games.
Bottoming out
Bottoming out is when a switch is fully depressed. Some switch designs (particularly rubber dome designs) require the switch to be bottomed out in order to actuate. Other switch designs will actuate at some point during travel before the bottom is reached. Bottoming out is often considered undesirable due to it slowing down the typist, and generating noise when the keycap hits against the keyboard's internals (sometimes referred to as 'clack'). Some switch designs are easier to not bottom out on than others, with factors such as key stiffness, the location of the tactile point and the force at which the mechanism springs upwards being relevant factors.
Switch characteristics
Some terminology is used to describe the behavior of the switch in regards to how the user experiences them. Any keyswitch with travel will fit into one of the following four categories. The last one being extremely uncommon.
Tactile switch
The most common type of switch - a tactile switch is a switch that has a 'bump' during travel. Usually the tactile point (i.e. the point at which the bump occurs) will occur around the point of actuation - in some designs it will occur exactly at the actuation point, but in many cases there isn't a perfect co-incidence.
More formally, tactility is a sudden drop in the amount of force needed to push the switch further. On a force graph of a tactile switch, the point of tactility will appear as a sudden drop in force. In broad terms, tactility in switching mechanisms is implemented by either pressing down on something that gives way or collapses (rubber domes, buckling springs, beam springs) or by adding in something that obstructs the travel of a linear switch (Alps CM or Cherry MX). Most keyboards for desktop or laptop computers will have tactile switches.
Linear switch
A linear switch is a switch that gets progressively stiffer during key travel, and thus has no tactile 'bump'. A force graph of an ideal linear switch will show a straight line rise of force from the start to the end of travel, but in practise the rate of force increase may be change at different points of the travel. Linear switch designs are simple and reliable, and are common in specially-designed rugged keyboards. They were very common in the 1970s and early 1980s for terminal and PC keyboards, but have been eclipsed by the popularity of tactile switches since the mid to late 1980s.
Clicky switch
A clicky switch is a type of tactile switch that is specifically designed to make some sort of auditory feedback when the tactile actuation point is reached during key travel.
Some clicky switches use a tactile mechanism that is inherently noisy (buckling spring, beam spring). Other switch families have special variants that are specially adapted to make a sound on actuation. For instance, in the clicky variations of the Alps CM, a leaf spring hits against the walls of the switch housing creating a sound. In the Cherry MX Blue, the slider is divided into two parts, with the lower part being propelled against the switch bottom when the tactile bump has been overcome.
Due to the fact that click mechanisms depend on the key travel overcoming some sort of obstruction, it is not possible to have a clicky linear switch. Some manufacturers attempted to get around this by using a beep speaker in the keyboard that makes a noise when the key is pressed.
Clicky switches should not be confused with those that are noisy to type on, but are not designed specifically to make noise to coincide with the tactile point.
See also: Category:Clicky switches.
Parabolic switch
A parabolic switch is a type of switch that follows a parabolic weighting curve. After reaching the peak of the parabola, the force to continue pressing down on the switch will actually decrease. This gives a very unique and consistent keyfeel as the low grade parabolas will provide an almost constant amount of force to be applied throughout the throw of the key switch. The actuation point can be anywhere on the parabola, but is usually placed 55-60% of the travel from the key idle state. Unfortunately this is usually after the crest of the parabola, so it becomes extremely difficult to avoid bottoming out in comparison to a linear switch.
Contact mechanism
A contact mechanism is the electrical mechanism in the switch used to register a key press by the keyboard's controller logic. Completely different switching mechanisms may use the same contact mechanisms – for example, rubber domes, Cherry MY switches and certain buckling spring implementations use a membrane contact mechanism despite the fact that these switches have otherwise completely different characteristics. Consequently terms such as "membrane keyboard" or "capacitive keyboard" are ambiguous, and should be avoided unless discussing the contact mechanism itself. Listed below are four of the most noteworthy ones.
