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Path: utzoo!watmath!clyde!burl!ulysses!ucbvax!hplabs!hp-pcd!bill
From: bill@hp-pcd.UUCP (bill)
Newsgroups: net.micro.pc
Subject: Re: Undocumented DOS Interrupts
Message-ID: <15200022@hpcvlo.UUCP>
Date: Thu, 8-May-86 14:36:00 EDT
Article-I.D.: hpcvlo.15200022
Posted: Thu May  8 14:36:00 1986
Date-Received: Tue, 13-May-86 00:38:29 EDT
References: <1310@umcp-cs.UUCP>
Organization: Hewlett-Packard - Corvallis, OR
Lines: 21
Nf-ID: #R:umcp-cs:-131000:hpcvlo:15200022:000:895
Nf-From: hpcvlo!bill    May  8 10:36:00 1986



Int 21h function 52h does exactly what you've already stated: it returns a
a pointer (in ES:BX) to a list of interesting DOS variables.  It's an
undocumented function because the table is considered version dependent.
(Some of the more significant variables are accessible through supported
DOS functions, like current drive, time variables, etc.)
The table also appears to contain stuff like number of disk drives,
DOS critical section flag, various buffer pointers, DOS segment, and so forth.

(Is that vague enough to keep back flames from Microsoft?)

I'm not sure of the exact purpose of Int 2Ah, but it appears to be somehow
used by our HP OfficeShare network software.  When I boot up my AT (3.2) 
without the network stuff, Int 2Ah points to an IRET.  With the network
installed, it points at CMP AH,0 / JNZ / MOV AH,1 / IRET / etc.

More information, anyone?

Bill Frolik
hp-pcd!bill