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From: dj@ctron.com (DJ Delorie)
Newsgroups: comp.os.msdos.programmer
Subject: Re: 8088 vs 8086
Message-ID: <1722@balrog.ctron.com>
Date: 21 Jun 91 12:30:33 GMT
References: <1991Jun21.030948.10951@cs.mcgill.ca>
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In article <1991Jun21.030948.10951@cs.mcgill.ca>, storm@cs.mcgill.ca (Marc WANDSCHNEIDER) writes:
> Could somebody please tell me the difference between the 8088 and the 8086
> processors..?
> 
> Obviously, both are 16bit processors, but is the width of the data bus the 
> only difference between them...?
> 
> Which was developed first, and why is it that the 386 and 486 chips create 
> virtual 8086s instead of virtual 8088s...?


Software differences:

  * Timing of opcodes, but only due to memory fetch times and
    instruction prefetch queue size.
    

Hardware differences:

  * 8-bit data bus vs. 16-bit data bus.

  (The 8088 had a "minimum" mode for 8085-ish compatibility; I don't
   recall if the 8086 had it also)

Same is for 80186 vs 80188.  I find that the only practical difference
is the cost of the external circuitry required.  With an 8088, you can
use one 8-bit ROM and one 8-bit RAM.  With an 8086, you need at least
two of each, with special circuitry to enable byte-wide writes.

As for the V86 mode, I *guess* that it's because the chip can do the
16-bit reads/writes you ask for, instead of 8-bit r/w.

I don't recall which was developed first, but my recollection is that
the original IBM PC had an 8088, and the IBM XT had an 8086.

DJ
dj@ctron.com