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From: dave@tygra.UUCP (David Conrad)
Subject: Re: 8086 vs. 80286 : How to detect which one?
Organization: CAT-TALK Conferencing System, Detroit, MI
Date: Mon, 1 Apr 91 08:06:59 GMT
Message-ID: <1991Apr1.080659.9077@tygra.UUCP>
References: <1991Mar26.223512.1@rulcri.leidenuniv.nl> <1991Mar28.094957.11834@tygra.UUCP>

In article <1991Mar28.094957.11834@tygra.UUCP> dave@tygra.UUCP (David Conrad) writes:
>In article <1991Mar26.223512.1@rulcri.leidenuniv.nl> vereijken@rulcri.leidenuniv.nl (Jan Joris Vereijken) writes:
>>Hi,
>>
>>
>>Actually, I want more, I want a way where I can decide wheter I'm dealing with:
>>
>>8088 / 8086 / 80188 / 80186 / V20 / V30 / 80286 / 80386 / 80486
>
>The only one I know how to do is 86,186,286 vs. 386,486 (the i586 is due out
>this year!).  The 386 only looks at the low 5 bits of CL when shifting (hey,
>the registers are only 32 bits wide, why would you need to shift farther
>than that!)  The earlier processors are not so smart.  They do what you tell
>them, even if it makes no sense (the way computers *should* work! :).
> 
>On 286's and previous all the bits would be shifted right out of AX, but on
>the 386, 486, and (presumably) 586 shl ax, 33 is equivalent to shl ax, 1, so
>AX ends up with 2 in it.  I don't know if the equivalent TPas would work:
> 
>     If (1 SHL 33) = 2 then
>       (* 386+ *)
>     else
>       (* 286- *);
> 
>Damn!  It produces 2 on my 286!?!  Either TP is too smart, or my information
>is wrong.  I got the info from a magazine, Dr. Dobbs I think.
>

Well, the problem was my memory was bad (in head, not computer).  As the
Turbo Assembler Quick Reference Guide tells me, the 80286/386 only allows
shifts of up to 31 bits for max. speed, but the 8086 allows 8 bits of
shift in CL.  So this is the right test, but it differentiates between
8086/8088 and later.  (Not sure about 186.)
 
Sorry to have posted incorrect information.

Dave Conrad
dave%tygra@sharkey.cc.umich.edu
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