A shell is a user interface for access to an operating system’s services. Mostoften the user interacts with the shell using acommand-line interface (CLI). The terminal is a program that opens a graphical window and lets you interactwith the shell.
Background
Originally, a computer terminal was an electronic or electromechanical hardwaredevice used for entering data into, and displaying data from, a computer or acomputing system. The terminal of the first working programmable, fullyautomatic digital Turing-complete computer, the Z3 (1941), had a keyboard and arow of lamps to show results.1
Early computers where huge machines taking up a lot of space. Commonly a systemconsisted of multiple cabinets, for example one cabinet for the main processorunit, one or more cabinets for tape drives, one cabinet for each disk drive, onecabinet for a punched card reader and one cabinet for a high speed printer. In thebelow image, a Univac 9400 system (1967) consisting of multiple cabinets isshown.
Teletypewriter (TTY)
Early user terminals connected to computers were electromechanicalteleprinters or teletypewriters (TeleTYpewriter, TTY). In the above image of theUnivac 9400 system, the cabinet marked UNICAC 9400 is the mainprocessor cabinet. The terminal is the machine looking like a huge typewriterplaced on the desk to the left of the main processor cabinet. Another example of an early terminal isthe Teletype Model 33 ASR (1963) shown below.
Video display terminal
As technology improved, teleprinter terminals was replaced by video displayterminals. One example of such a video display terminal is the DEC VT100 (1978)shown below.
Note that the DEC VT100 terminal shown above is not a computer. The DECVT100 terminal wasonly used for input and output to and from a connected computer. In the below image DEC VT52 video terminal (1974) is connected to a PDP 11/55 computer (1975).
Terminal emulator
A terminal emulator is a program that emulates a video terminal within someother display architecture.2 Today, the term terminal isoften used synonymously with a terminal emulator running a shell.
