Mail Archives: djgpp/1997/08/31/15:54:48

From: Temujin <temujin AT sentex DOT net>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Dos Version 6.20 and 6.21
Date: Mon, 25 Aug 1997 12:33:52 -0700
Organization: Sentex Communications
Lines: 23
Message-ID: <>
References: <5to298$5js AT hyperion DOT triode DOT net DOT au>
Mime-Version: 1.0
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

Andrew Happ wrote:
> ========
> I've been looking at the difference between these 2 MSDOS releases.  A
> file compare between the respective versions of IO.SYS and MSDOS.SYS
> reveals no difference, although the build dates do vary.  Comparing
> the  two COMMAND.COMs reveals identical code except for two op codes,
> vis
> DOS 6.20 uses
>   XCHG   AH,AL
>   XOR     AH,AH

This basically acomplishes nothing, if AL is moved into AH and then
zeroed out, the XCHG line is an extra useless line.

> DOS 6.21 uses
>   XOR   AH,AH
>   MOV   AL,15
> Does any machine code buster or os guru know what this difference
> means in terms of the command processor's operation?

- Raw text -

  webmaster     delorie software   privacy  
  Copyright 2019   by DJ Delorie     Updated Jul 2019