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From: guy@gorodish.UUCP
Newsgroups: comp.unix.questions
Subject: Re: Multiscreen on Unix
Message-ID: <20550@sun.uucp>
Date: Sun, 7-Jun-87 04:23:02 EDT
Article-I.D.: sun.20550
Posted: Sun Jun  7 04:23:02 1987
Date-Received: Sun, 7-Jun-87 20:03:59 EDT
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> Windows and multiple screens are not the same thing.
> 
> My UNIX PC has windows.  You can create them, then you can reshape them
> and move them.
> 
> My Microport System V/AT has multiple screens.  You can's reshape them
> amd move them.

I presume "You can's reshape them and move them" really should have
read "You can't reshape them or move them".

> The difference is like night and day.  On my UNIX PC, it's so much
> of a bother to use multiple windows that I got rid of them altogether.
> It's no fun pressing keys here and there, then finding the mouse,
> then location a corner here and here, and then finally (a few minutes
> later) getting a new window to work in.
> 
> On my Microport system, I can hit a key and be working on a fresh new screen
> in about 50 milliseconds.  I don't waste time finding keys and mice, and
> I don't waste screen space on fancy but useless borders.

There is nothing about a window system that obliges you to have
"fancy but useless borders".  There is also nothing about a window
system that obliges you to use mice or multiple keystrokes (you will
*still* have to find the one key that gets you a new screen, even on
your Microport system, although it may be placed so that "finding" it
is trivial) to create a new window, or that requires the creation of
a window to take minutes.  (Yes, I know, SunView puts stuff on the
borders and can take a while to create windows, and may not make it
possible to pop up a new window and move to that window in one
keystroke.  I'm saying what's possible here.)

> But it's good to be precise in our terminlogy, and I just wanted to
> emphasize that:
> 
>      WINDOWS AND MULTIPLE SCREENS ARE NOT THE SAME THING.

Multiple screens are just windows that are obliged to cover the
entire screen; in other words, a multiple-screen system is just a
window system with a number of restrictions.  The only fundamental
difference between a multiple-screen system and a general window
system is that a multiple-screen system doesn't have to arrange to
multiplex the display, and can possibly use tricks to multiplex the
keyboard.

The person requested multiple screens "on UNIX".  The only way to do
this "on UNIX", rather than on a particular UNIX machine or set of
UNIX machines, is to assume that all you have available is a dumb
terminal.  Doing so requires you to do things like maintaining
virtual screens, separate from the physical screen; after doing this,
the extra work of supporting non full-screen windows isn't much.  All
that you'd get from not making that step is that you wouldn't have to
worry about having programs capable of dealing with variable-size
screens, and there are even ways of providing some of that by playing
games with things like the TERMCAP or TERMINFO environment variables.

In the particular case of a PC, there may be tricks you can play with
multiple screens that won't work with windows.  The programs running
in the "active" window can be given direct access to the screen, and
when switching screens you can just copy the entire screen image to a
holding buffer; you could just freeze programs running in inactive
windows, and thus not have to worry about multiplexing input or
output.
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com