Optional history lesson (Unix part 1A)
Both the Unix operating system and the word "terminal" date back to the days before small personal computers, when users sat at devices called terminals connected to one multi-user mainframe computer. A program like "Terminal" on the Macintosh "emulates" one of those old terminals.(See terminal emulator.) The earliest terminals had no "CPU" chip of its own, just a keyboard and display; the display could be either a printer or a screen. It might display only upper-case characters in a single type font, with no "what you see is what you get" touches, like bold or underlined text. Those terminals also had much simpler keyboards than today's Macs and PCs. (That's why some of those keys may not do anything when you are inside a terminal-emulator program.)Those basic terminals were designed to enter commands one line at a time, which is why an important key is marked "Enter" on some keyboards and "Return" on others. "Return" was the typewriter word for "return to the start of a line," and the first terminals really were little more than teletype-style typewriters. You typed something; the computer typed back something. When more sophisticated terminals became available, the old ones were sometimes called "dumb terminals."
The early video display terminals, which were a little smarter, had model names like "VT52" and "VT100." They still had no mice, so the keyboard was the only way to give instructions to the computer, either by typing on a "command line," or by running programs that recognized special key combinations to control the program.
That's the origin of the key labeled "control" that we still have on Macs and PCs today, and you can still use it to perform special functions within Unix programs.
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