Unix people hated to admit it at the time, but when it was created, Unix really was a mainframe operating system like IBM's, and it supported multiple simultaneous users via timesharing. Each user communicated with the central computer through separate, standalone terminals, especially those from the Digital Equipment Corporation's VT series.
These terminals did not display the graphical desktops that have been mainstream since 1995 so. They were text-only devices, typically presenting 25 lines of 80 characters each, without icons or windows. Some applications used the full screen, presenting numbered menus and fill-in fields for data entry. The bulk of the Unix software tools, especially those used by programmers, were controlled from the command line, and sent back scroll-up-from-the-bottom output.
Linux works the same way. Put most simply, Linux is Unix. Linux does not use external ''dumb terminals'' like the 1970s DEC VT100, but the DEC-style terminal-oriented software machinery is still there inside Linux and still functioning, in the form of terminal emulation.
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