Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!mcgill-vision!bloom-beacon!snorkelwacker!usc!samsung!think!masscomp!jeffj
From: jeffj@masscomp.ccur.com (Jeff Jonas)
Newsgroups: comp.binaries.ibm.pc.d
Subject: Re: Sys Req - key.
Summary: the 'sys req' key has it's origin in earlier equipment
Keywords: What is it for?
Message-ID: <5604@masscomp.ccur.com>
Date: 19 Dec 89 00:36:36 GMT
References: <187@nmtvax.nmt.edu> <216@edpmgt.UUCP>
Organization: CONCURRENT COMPUTER CORP. WESTFORD MA
Lines: 34

In article <216@edpmgt.UUCP>, gpitcher@edpmgt.UUCP (Glenn Pitcher) writes:
> In article <187@nmtvax.nmt.edu>, jeff@nmtvax.nmt.edu (- Jeff -) writes:
> > This is probably a useless question, but there is a mysterious key on my 
> > XT-keyboard called the 'Sys Req' key. I've seen this key on many other ...

> If I remember correctly, the sys-req is a key that is used on the big IBM's
> (303x, 308x).  Now, you asking, "well, why then is this key on my PC 
> keyboard?"  Well, glad you asked.  Very early on in the PC's life, there 
> were a couple of specialized products that were produced.  These were called
> the 3270 PC and PC/370(?). 

I remember in high school, we had a big RJE terminal
(keyboard, printer and card reader).
In the IBM tradition of "speak when you are spoken to",
the keyboard was disabled until the controller was ready to listen.
The 'sys req' key requested keyboard input,
and the keyboard was then unlocked for input
(yes, all the other keys were disabled until the keyboard was selected).

Perhaps there were batch systems intended for the PC  :-)

So far, all responses confirm that 'sys req' is an out of band signal,
so it was intended to have an important function.
I guess an underutilized function is better than an overutilized
function, where applications would fight over control of the key interrupt.


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