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From: markc@wpi.wpi.edu (Mark B. Cohen)
Newsgroups: comp.binaries.ibm.pc.d
Subject: Re: Sys Req - key.
Keywords: SysReq
Message-ID: <6075@wpi.wpi.edu>
Date: 7 Dec 89 17:10:46 GMT
References: <187@nmtvax.nmt.edu> <1989Dec5.190738.17084@ux1.cso.uiuc.edu> <20358@pasteur.Berkeley.EDU> <1989Dec6.054648.17589@usenet.ins.cwru.edu>
Reply-To: markc@wpi.wpi.edu (Mark B. Cohen)
Organization: CS Dept., Worctechnic Polyester Institute, Worcester, MA
Lines: 22

In article <1989Dec6.054648.17589@usenet.ins.cwru.edu> 
  trier@skybridge.scl.cwru.edu (Stephen Trier) writes:
]Peter Norton's _Programmer's_Guide_to_the_IBM_PC_and_PS/2_ contains a pretty
]complete description of the Sys Rq key.  The key is apparently meant to be
]used for operating systems, perhaps as a hot key to switch between virtual
]terminals or to suspend a process and return you to a shell.  When it is
]pressed, the BIOS does an Int 15H with AH=85H and AL=00H.  When the key is
]released, it does the same interupt, but with AL set to 01H instead.  That
]way, your program can use it as a shift key, kind of like Alt.
]
]Apparently, very few (if any) programs or operating systems use the key.

For Microport's System V/AT with DosMerge, the SysReq key _is_ used
to switch between virtual terminals under UNIX, or between DOS and
UNIX screens when using a Merge (DOS) application.  

I know some other PC compatible UNIX's have this feature.  I don't know 
if they also use the SysReq key.  Microport is now defunct.
-- 
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