Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!ukma!psuvm.bitnet!cunyvm!ndsuvm1.bitnet!nu013809
From: NU013809@NDSUVM1.BITNET (Greg Wettstein)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Interesting 80X86 instruction
Message-ID: <255NU013809@NDSUVM1>
Date: Mon, 10-Aug-87 08:08:25 EDT
Article-I.D.: NDSUVM1.255NU013809
Posted: Mon Aug 10 08:08:25 1987
Date-Received: Fri, 14-Aug-87 00:55:16 EDT
References: 767@custom.UUCP
Organization: North Dakota Higher Education Computer Network, Fargo, ND
Lines: 18
DISCLAIMER: Author bears full responsibility for contents of this article.


I don't know how factual the following comment is but I have heard a
rationale for the two byte instruction which implements the AAD operation.
     
Folklore has it that when the 80x86 chipset was designed the chip designers
got caught in a microcode storage bind.  Rather than wasting valuable
micro-code space they simply setup the AAD class of instructions to carry
the parameter for the adjustment in in-line code rather than coding the
full instruction in microcode.
     
Whether this is true or not may be the subject of much debate.  However
it provides an interesting story if nothing else.
     
     
                                        As always,
                                        G.W. Wettstein