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From: trier@wrangell..scl.cwru.edu (Stephen Trier)
Newsgroups: comp.binaries.ibm.pc.d
Subject: Re: Sys Req - key.
Keywords: SysReq
Message-ID: <1989Dec6.060703.19022@usenet.ins.cwru.edu>
Date: 6 Dec 89 06:07:03 GMT
References: <187@nmtvax.nmt.edu> <1989Dec5.190738.17084@ux1.cso.uiuc.edu> <20358@pasteur.Berkeley.EDU>
Reply-To: trier@skybridge.scl.cwru.edu (Stephen Trier)
Organization: Smith Undergrad Lab, CWRU, Cleve., OH
Lines: 12

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.

                         <=> Stephen Trier    sct@po.CWRU.Edu
                                              trier@skybridge.scl.CWRU.Edu