What Are Auto-Repeat Keys on an IBM PC Keyboard?

Auto-Repeat: The Standard Behavior of PC Keyboard Keys

On the original IBM PC (Model 5150, 1981) and all compatibles since, every alphanumeric and most control keys repeat automatically when held down. This feature is called auto-repeat (or typematic repeat).

How It Works

• Delay: After initial press, a pause (~500 ms default) before repeat starts.
• Rate: Repeat frequency (~10–30 Hz default).
• Both parameters are programmable via BIOS (INT 16h AH=03h) or OS (Windows: Control Panel → Keyboard; Linux: xset r rate).

Exceptions

• Modifier keys (Shift, Ctrl, Alt, Win) do not auto-repeat.
• Lock keys (Caps Lock, Num Lock, Scroll Lock) toggle on press, no repeat.
• Some specialty keys (Print Screen, Pause) may not repeat depending on BIOS.

Why It Exists

Enables rapid character entry (holding 'x' for a line of x's) and continuous cursor movement (holding arrow keys) without multiple keystrokes—a UX staple since the 1980s.