The break key originated from telegraphs and was used to interrupt the signal. It later appeared in teletype machines and computers, with various functions. Modern keyboards have a pause/stop key combination with different uses depending on the program or operating system.
The break key found on many modern keyboards has a history that can be traced back to telegraphs. This early use of an interrupt key was actually a switch that could be used to bridge contacts within a telegraph machine and send a constant signal when not in use. Later examples of break keys existed in early teletype machines and computers that used a time-sharing scheme. Modern personal computers have also included break keys in many keyboard designs and have had a variety of functions. Most modern keyboards have a pause/stop key combination that can stop text output or exhibit different behavior, depending on the program you’re using.
Telegraphs enabled long-distance communication by electrically connecting two machines via a wire. These devices were operated by pressing a button to make and successively break an electrical connection in a specific pattern that could be interpreted to represent numbers and letters. When not in use, the signal was typically sent continuously to indicate that the transmission line was functional. Before transmitting a message, a break switch or key might be activated to break the connection.
Later teletype machines also included a break key which could be used to alert the operator that a message would soon be transmitted. The break key in this circumstance typically sent a special, nonprinting character that could wake up the remote machine before sending an actual message. This same key and non-printing character also had a use in timeshare computers, as it could often be used to break or terminate a modem connection.
Some early microcomputers also had interrupt keys, although the functionality was usually different. These abort keys were sometimes used to initiate warm restarts of the system or cold restarts when used in conjunction with other keys. Microcomputers lacking break keys were sometimes able to simulate their functionality with a different key combination.
Modern computers often have a combined pause/stop key, although its function is not universal across operating systems (OSs) or even programs. Some computers use the pause/stop key to stop displaying text in the disk operating system (DOS) or other similar environment. A common use of this is to press pause/pause during boot to read text output from the basic input/output system (BIOS). It can also be useful when using a DOS box or terminal window that has a limited number of display lines and no scrolling options. In other circumstances, the key is used to interrupt a program or, in combination with another key, to display information.
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