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From: timd@hotwheel.dell.com (Tim Deagan)
Newsgroups: comp.sys.ibm.pc.hardware,comp.sys.intel
Subject: Re: Question -- 386DX versus 386SX
Message-ID: <14964@uudell.dell.com>
Date: 7 Feb 91 22:22:54 GMT
References: <1991Feb7.182436.17262@athena.cs.uga.edu>
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Reply-To: timd@hotwheel.dell.com (Tim Deagan)
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In article <1991Feb7.182436.17262@athena.cs.uga.edu>,
boone@athena.cs.uga.edu (Roggie Boone) writes:
> I know this has probably been asked before, but I am new to this group.
> 
> Could someone please explain or direct me to an article that explains in 
> some detail the difference(s) between a full 80386 microprocessor
> (80386DX) and the 80386SX?  Are they both 32-bit processors?  I've 
> heard that the main difference is that the SX "talks" to the outside 
> world (memory, disk, etc) at 16-bits while the DX uses 32 bits.  Is this
> true and is this the only difference?  Are there any limitations on 
> the 386SX running 386-specific software?
> 
> _Any_ info that can be provided (technical or not) would be appreciated.

Your description of the difference is accurate.  Internally the SX and DX
have the same bus, 32-bits.  All the internal registers are the same, as 
are the protected mode features.  To the outside world the SX looks the same
as a 286, a 16-bit external bus.  Perfectly adequate for all the ISA (AT) bus
cards out there now.  This is the same trade-off INTEL made when they started
the whole PC thing by taking the 8086 16-bit processor and making an external
8-bit version called the 8088.
The SX comes in two official flavors, 16 and 20 MHz.  Most DX's are 20
or 25 MHz.
The SX has had some reported problems with protected mode applications such as
WIN 3.0, but most all of these have been traced down to the chip-set the
CPU was
glued to.  There is one technical consideration with 386SX's, it'll only matter
to HW developers but it is frustrating, the SX only comes in one package, 
PQFP, the Plastic Quad Flat Pack.  Only one company sells a chip-clip and it
costs hundreds of dollars and takes 6-8 months to ship, if ever.  So, hardware
debugging is a MAJOR bitch.  Small point, but it can completely stymie
development
in a pinch (inverse assembling and such is impossible).
There are some differences such as prefetch queue size which are invisible and
probably won't matter to anyone.  Price wise the SX, especially with caching,
can be a good deal.  It all depends on what you want to do.  I'd probably
buy one if the price were right.


------------------------------------------------------------------------
------------------"Wake up!  Wake up!" - Spike Lee ---------------------
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                         Rev. Tim Deagan
                     timd@hotwheel.dell.com
                     timd@twaddle.dell.com