IBM in the AIX that ran on the 370/PS2/i860 had a
device called the
High Function Terminal that allowed you to swap screens on the
The HFT continued on the POWER RS/6000s.
I got intrigued by the fact on those systems you could
have a “shell”
that persisted across logins and could be detached and reattached on
another device at another time. I set about making such an
implementation. Not particularly efficient, it essentially grabbed
one of the BSD ptys and spawned the shell there and then a small
alternative login shell forwarded the real tty to that. You could
then detach it leaving the shell running on the PTY and reattach it
elsewhere. Much like ITS, on. login it reminded you that you had a
detached shell running and offered to reattach it rather than spawning
a new one (complete with the ITS-ish: space for yes, rubout for no).
It never really caught on.
It sounds like what screen(1), byobu(1), tmux(1), etc., do today except
the user normally runs the program from the shell after logging in
though I expect some of them support being chsh'd to being the log-in
Acorn's RISC iX, their 4.3 BSD launched in ’89 and running on their
ARM2, had what they called ‘virtual terminals’ where the user could
switch to one of several TTYs using the keyboard; getty would be
waiting. Similar to Linux today. What early systems had this idea
as a means of multiplexing terminals to a single user?