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From: std-unix@ut-sally.UUCP
Newsgroups: mod.std.unix
Subject: Re: job control
Message-ID: <5979@ut-sally.UUCP>
Date: Fri, 10-Oct-86 16:18:00 EDT
Article-I.D.: ut-sally.5979
Posted: Fri Oct 10 16:18:00 1986
Date-Received: Sat, 11-Oct-86 04:50:45 EDT
References: <5932@ut-sally.UUCP> <5965@ut-sally.UUCP>
Organization: IEEE P1003 Portable Operating System for Computer Environments Committee
Lines: 40
Keywords: POSIX Appendix C
Approved: jsq@sally.utexas.edu
Summary: consider the virtual console paradigm as well

From: campbell%maynard.UUCP@harvisr.harvard.edu (Larry Campbell)
Date: Fri, 10 Oct 86 00:52:48 EDT
Organization: The Boston Software Works, Inc.

There's another flavor of terminal I/O multiplexing that Mark Horton
didn't mention.  It's widely available today; it requires no changes
to user mode code (in fact, its presence is not detectable by user
mode code); it does not require bit mapped or graphics terminals; and
I've found it to be more useful and pleasant than I would have guessed.

"It" is the "virtual console" feature found in most PC-based UNIX
implementations.  This does rely on memory-mapped video, but character-
mapped terminals work as well as bit-mapped ones.  Typically, four to
ten function keys are used to select four to ten virtual consoles.
Each virtual console occupies the entire physical screen;  you can
only see one at a time.  Keyboard input goes to the current (visible)
virtual console.  Since the video is memory mapped, switching is
instantaneous.

A process trying to write to a non-current virtual console will (fill
up some clists and then) block.  A process trying to read the keyboard
will block until the user switches to its console and types something.

This is all completely invisible to user programs;  they think they're
dealing with a perfectly ordinary 24x80 terminal.  No SIGTSTP, no window
size ioctls, etc.

I've used several "true" windowing systems before (Xerox Star, Apple
Macintosh, Microsoft Windows, Symbolics 3600) and I find I like the
virtual console paradigm far more than I would have anticipated.  It's
simple and uncluttered.

I'm not suggesting that virtual consoles become part of the standard;
just pointing out a useful alternative design.
-- 
Larry Campbell            MCI: LCAMPBELL   The Boston Software Works, Inc.
ARPA: campbell%maynard.uucp@harvard.ARPA   120 Fulton Street, Boston MA 02109
UUCP: {alliant,wjh12}!maynard!campbell     (617) 367-6846

Volume-Number: Volume 7, Number 46