PC Keyboard Technology

The keyboard is the main device for typing text and issuing commands to a computer. Inside it, the keys are arranged over a grid of electrical contacts called a matrix. When a key is pressed, it closes a connection at the intersection of a particular row and column, and a small controller chip inside the keyboard detects which connection changed. This matrix design lets a keyboard with many keys be read using far fewer wires than one connection per key would require.

Rather than sending the letter printed on a key, the keyboard reports a numeric value called a scan code. The controller generates one code when a key is pressed and another when it is released, so the computer can tell how long a key is held and detect combinations of keys held together. Software in the operating system then translates these scan codes into the characters or actions appropriate to the current keyboard layout and language.

The keyboard communicates with the computer over a dedicated connection. Older designs used a round connector and a simple serial link to a keyboard controller on the motherboard, while later keyboards commonly connect over USB. Because the keyboard sends standardised scan codes rather than finished characters, the same physical keyboard can be used with different layouts simply by changing the translation the software applies, which is how one keyboard can serve many languages.

Frequently asked questions

What is a scan code?

It is the numeric value a keyboard sends to identify which key was pressed or released, which software then translates into a character or action.

Why does a keyboard send codes instead of letters?

Sending codes lets the same keyboard work with any language or layout, since the software decides which character each code represents.

How does the keyboard detect which key was pressed?

Keys sit over a grid of contacts, and pressing one closes a connection at a specific row and column that the keyboard’s controller identifies.