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A mechanical keyboard uses an individual switch mechanism beneath each key. In a conventional contact switch, pressing the key moves a stem, compresses a spring, and closes electrical contacts. The keyboard’s electronics detect the change, firmware interprets it, and a report carries input to the computer. CHERRY, QMK, and the USB Implementers Forum explain these separate stages.
If you are new to keyboards, understanding the working of a mechanical keyboard starts with following one press and release. This guide explains the parts, sensing methods, and input-processing stages you will encounter in keyboard descriptions.
Key takeaways
- The keycap, stem, and spring handle physical movement.
- Contact closure, magnetic sensing, and optical sensing are different ways to detect input.
- Firmware connects detected changes to assigned key functions.
- Ghosting, rollover, and hot-swap describe separate capabilities.
This is a documentation-based explanation, with named manufacturer examples. It does not draw on hands-on performance testing.
On this page: Parts beneath a key · The press-and-release sequence · Feel and sensing · Ghosting and rollover · Hot-swap · Specification checklist · Common questions
Parts beneath a mechanical key
A conventional CHERRY MX contact switch provides a useful starting example. Its mechanism separates the surface you touch from the parts that move and the contacts that register input. CHERRY’s technology explanation describes these roles:
| Part | Main responsibility |
|---|---|
| Keycap | Provides the surface you press and moves with the switch mechanism. |
| Stem | Moves downward inside the switch and operates the contact mechanism. |
| Spring | Compresses during the press and returns the stem when pressure is released. |
| Electrical contacts | Close a circuit when the mechanism reaches its actuation point. |
| Printed circuit board, or PCB | Carries the electrical connections associated with the switch. |
| Controller | Reads the keyboard’s electrical state under firmware control. |
The controller’s role is explained in QMK’s matrix documentation. Firmware is the software that controls this processor, and a keymap associates keycodes with positions in the physical layout, as defined in the QMK glossary.
These roles explain why a switch is only part of the input system. Its moving parts create a detectable change; the controller and firmware determine how that change becomes keyboard input.
How a key press becomes computer input
The following sequence uses a conventional contact switch and QMK as a firmware example. QMK documents one implementation; another keyboard may organize its processing differently.
1. Movement reaches the actuation point
You push the keycap downward, moving the stem and compressing the spring. At the actuation point—the point where input is triggered—the mechanism closes the electrical contacts. CHERRY explains that this can happen before the key reaches the end of its downward travel, commonly called bottoming out. Source: CHERRY
Actuation and bottoming out therefore describe different events. One concerns detection; the other concerns how far the key has physically traveled.
2. The controller scans the switch matrix
A switch matrix is an electrical arrangement of rows and columns. In QMK’s example, pressing a switch connects its row and column, and the controller checks those connections to identify the pressed position. This repeated checking is called matrix scanning. Source: QMK matrix explanation
Think of a matrix position as an address for a switch. Finding that address tells the firmware which position is active; assigning a keyboard function comes later.
3. Debouncing handles contact transitions
Metal contacts may make several brief electrical transitions as they settle during a press or release. QMK calls this contact bounce, or contact chatter, and describes hardware and software methods for handling it. Without mitigation, those transitions can be interpreted as repeated actions. Source: QMK contact-bounce documentation
In QMK, software debouncing runs after raw matrix scans. Its purpose is to interpret unstable electrical transitions appropriately. The tactile bump you feel in some switches is a separate physical characteristic.
4. Firmware interprets the position and change
QMK maps matrix positions to the physical layout and assigned keycodes. It also compares previous and current scan results to identify presses and releases, then processes records of those changes. Source: Understanding QMK’s Code
For a simplified example, imagine a position assigned to a letter key. The scan identifies the position, while the keymap supplies its assigned function. That distinction helps explain how firmware can associate a physical key with a particular action.
5. A USB HID report carries input to the host
For a keyboard using USB Human Interface Device, or HID, reporting, input is represented in report data. The USB Implementers Forum explains that HID usages identify the purpose and meaning of report fields, while the HID class definition specifies how a driver extracts device data. Source: USB-IF HID documentation
Together, the firmware and HID explanations show the path from detected switch activity to computer-readable input. The electrical contact itself does not produce a finished character directly inside an application.
6. Release produces another state change
When you lift your finger, the spring returns the stem and the contact switch returns to its unpressed state. QMK detects the change between scan results and processes the release. Sources: CHERRY and QMK
A complete tap therefore includes both a press and a release. Following both makes the mechanism easier to understand than stopping at the moment of actuation.
Switch feel and sensing technology
Switch descriptions answer two useful questions: What does the movement feel like? and How is that movement detected? CHERRY describes linear, tactile, and clicky variants, while Wooting and Corsair document different sensing approaches.
Within CHERRY’s explanation, linear switches lack a distinct tactile bump or deliberate click feedback, tactile switches provide a bump, and clicky switches add an audible click. These terms describe feedback during movement. Source: CHERRY
The detection method is a separate question:
| Documented example | How input is detected | What to take from the example |
|---|---|---|
| Conventional CHERRY MX contact mechanism | Stem movement closes electrical contacts connected to the PCB. | Contact closure is the sensing event in this example. |
| Wooting’s historical Hall effect explanation | A magnet moves with the stem above a sensor on the PCB. Positioning, calibration, and firmware affect interpretation. | Magnetic sensing requires a matching sensor and processing system. |
| Corsair OPX Low-Profile optical switches | An interrupted infrared beam signals actuation. Corsair describes a black metal light shield used in that interruption. | This named optical design detects a change in light. |
Sources: CHERRY; Wooting, May 10, 2019; Corsair, updated March 17, 2026.
Wooting’s article is useful historical evidence for the magnet-and-sensor mechanism. Its old specifications should not be treated as current specifications for every Hall effect keyboard. Likewise, Corsair’s beam-interruption explanation applies here to OPX Low-Profile specifically.
For a particular keyboard, identify both its switch feedback and its detection system. Neither description alone establishes compatibility, simultaneous-key reporting, or total input latency.
Ghosting and rollover
Ghosting concerns false matrix paths
Ghosting occurs when a matrix arrangement produces an apparent press at a position you did not press. QMK illustrates this with a small matrix in which three closed switches create an unintended path that makes a fourth position appear active. Source: QMK matrix explanation
Here is the same idea with simplified labels:
| Conceptual matrix | Column A | Column B |
|---|---|---|
| Row A | A: pressed | B: pressed |
| Row B | C: unpressed | D: pressed |
In the illustrated arrangement without diode isolation, pressing A, B, and D can make C appear pressed. QMK shows how per-switch diodes, which allow current in one direction, prevent that unwanted path in its example. This is a circuit explanation; individual mechanical switches alone do not establish ghosting prevention.
Rollover concerns overlapping input
Rollover describes pressing a key while another remains held. N-key rollover, or NKRO, describes the capability to report any number of simultaneous key presses, according to the QMK glossary.
Use separate questions when reading a keyboard description: Can its sensing circuit distinguish the pressed positions correctly? Can its reporting system convey the simultaneous inputs? A switch’s linear, tactile, or clicky feel does not answer either question.
What hot-swap means
Hot-swap describes switch replacement without soldering on a keyboard designed for compatible replaceable switches. CHERRY specifically discusses replacing standard MX switches on hot-swap keyboards. Source: CHERRY
Treat it as a capability of the board, socket, and supported switch combination. Before choosing replacement switches, check the keyboard manufacturer’s exact compatibility information, including the supported switch family and profile. A hot-swap label by itself does not establish interchangeability among contact, optical, magnetic, or low-profile systems.
A practical keyboard specification checklist
Use this checklist beside a keyboard’s official documentation. It turns broad feature labels into questions you can answer before drawing conclusions.
- Movement: Which words describe the feedback—linear, tactile, or clicky? Keep those separate from the sensing method.
- Detection: Does the documented design use electrical contacts, a magnetic sensor, or optical sensing? Record the exact model or switch family.
- Processing: If debounce is mentioned, what signal issue does it address? QMK’s contact-bounce explanation shows why this belongs to electrical processing.
- Timing: If a scan rate or report rate is advertised, which stage does it describe? Look for a complete measurement method before treating it as total input latency.
- Capabilities: Verify rollover and hot-swap separately. For replacement switches, look for an explicit compatibility statement.
The checklist combines CHERRY’s switch descriptions, QMK’s processing explanation, debounce documentation, and USB-IF’s reporting explanation.
For example, an optical actuation claim answers a question about detection. You still need information about the controller, firmware, reporting, and host processing to assess the full input path. The named sensing technology alone cannot establish zero end-to-end delay.
Common questions
Does every mechanical keyboard click?
No. CHERRY distinguishes linear, tactile, and clicky switches. A deliberate click is a feature of the clicky category; tactile feedback and electrical detection are separate concepts. Identify the exact switch variant when interpreting a keyboard description, since the broad mechanical label does not specify click feedback. Source: CHERRY
Is debounce the bump you feel?
No. Contact bounce is a series of brief electrical transitions as contacts settle. Debouncing handles those transitions through hardware or software. A tactile bump describes physical feedback during switch movement. QMK’s debounce documentation and CHERRY’s switch descriptions address these different parts of keyboard operation. QMK, CHERRY
Can every mechanical keyboard accept replacement switches without soldering?
No. CHERRY describes solder-free replacement for standard MX switches on hot-swap keyboards. Check whether your exact board supports hot-swap and which switches it supports. The presence of individual switches does not establish that a keyboard has compatible sockets or supports the replacement family you want. Source: CHERRY
Putting the mechanism together
A mechanical keyboard combines individual moving switch mechanisms with electronics that detect and interpret input. For the conventional contact example, the useful sequence is movement → contact closure → scanning and debouncing → key mapping → host reporting, followed by release processing. CHERRY, QMK, QMK debounce documentation, and USB-IF support those stages.
For your next step, apply the checklist to one keyboard’s official documentation and identify what each specification actually describes.
Source basis: manufacturer explanations and technical documentation captured October 15, 2026. The Wooting mechanism article was published May 10, 2019; the Corsair OPX Low-Profile article was updated March 17, 2026.