Break key

In modern usage, the key has no well-defined purpose, but while this is the case, it can be used by software for miscellaneous tasks, such as to switch between multiple login sessions, to terminate a program, or to interrupt a modem connection.

The teleprinter operated in a very similar fashion except that the sending station kept the loop closed (logic 1, or "marking") even during short pauses between characters.

Holding down a special "break" key opened the loop, forcing it into a continuous logic 0, or "spacing", condition.

The computer (specifically the UART) recognized this as a special "break" condition and generated an interrupt that typically stopped a running program or forced the operating system to prompt for a login.

Although asynchronous serial telegraphy is now rare, the Break key once used with terminal emulators can still be used by software for similar purposes.

It does not trigger an interrupt but will halt any running BASIC program, or terminate the loading or saving of data to cassette tape.

Because of the BBC Micro's near universal usage in British schools, later versions of the machine incorporated a physical lock on the Break key to stop children from intentionally resetting the computer.

[8][6] While both Ctrl+Break and Ctrl+C combination are commonly implemented as a way of breaking the execution of a console application, they are also used for similar effect in integrated development environments.

Break/Pause key on PC keyboard
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