Mechanical typewriter shift lock is typically set by pushing both Shift and lock at the same time, and released by pressing Shift by itself. Computer CAPS LOCK is set and released by the same key, and the CAPS LOCK behavior in most QWERTY keyboard layouts differs from the Shift lock behavior in that it capitalizes letters but does not affect other keys, such as numbers or punctuation. Some early computer keyboards, such as the Commodore 64, had a Shift lock but no CAPS LOCK; others, such as the BBC Micro, had both, only one of which could be enabled at a time.