Guides · 4 min read

What happens when you press a key

A key press feels instant, but a few small parts take turns to make it happen. Knowing them explains why a light touch types just as well as a hard one.

Fig. 2Inside a key switch
Click and hold, press a key, or drag the slider0.0 mm down · 30 g · contact open
  • moves when you press
  • signal once the contact closes
A common linear switch, cut in half. The key can go down 4 mm, but it registers at 2 mm: there the tab on the stem slides past the metal contact, the contact closes, and the controller chip tells the computer. The spring pushes back about 45 g at that point. Everything after 2 mm is extra, which is why a light, quick press is enough.

The parts of a key switch

  • Keycap. The part you touch. It sits on the stem and only carries your finger’s push.
  • Stem. A plastic slider that moves straight down inside the switch housing. A tab on its side holds the metal contact open while the key is up.
  • Spring. Pushes the stem back up when you let go. The further down the key goes, the harder it pushes back.
  • Contact. Two thin metal leaves. When the stem’s tab slides past, one leaf springs across and touches the other, and a small current can flow.
  • Circuit board and controller. The keyboard’s chip notices the closed contact and sends the key to the computer, usually over USB or Bluetooth.

Why the key registers halfway down

On a common mechanical switch the key can travel about 4 mm, but the contact closes at about 2 mm. That point is called the actuation point. The rest of the travel is only there so the key doesn’t stop suddenly. Pressing all the way to the bottom (“bottoming out”) doesn’t send the key any sooner; it just takes more effort and, over a long session, tires your fingers.

What the controller does

The keys are wired in a grid of rows and columns, and the controller checks the grid many times a second to see which contacts are closed. Metal contacts bounce for a few thousandths of a second when they close, so the controller waits for the signal to settle before it reports the key once. Then the computer turns the key into a character using your keyboard layout, which is how the same key can type a Q on QWERTY and an apostrophe on Dvorak.

Other kinds of keyboards

Most laptop and office keyboards don’t use separate switches. Under each key is a small rubber dome; pressing it makes the dome collapse and push two thin layers of circuit together. Laptop keys often add a scissor-shaped frame so the key stays level, and they travel only 1 to 2 mm. The idea is the same: the key counts once a contact closes, not when it hits the bottom.

What this means for your typing

  • Press each key just far enough for it to register, then let it come back up. A light touch is faster and less tiring.
  • Keep your fingers relaxed and lightly curved over the home row, so each press is a short movement.
  • Any keyboard works for learning. Touch typing is about which finger presses which key, explained in the finger placement guide.
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