Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!strath-cs!cs.glasgow.ac.uk!bru-cc!md89mch
From: md89mch@cc.brunel.ac.uk (Martin Howe)
Newsgroups: comp.sys.intel
Subject: Re: Difference between a 386 and a 386sx
Keywords: 386 386sx
Message-ID: <1824@Terra.cc.brunel.ac.uk>
Date: 21 Sep 90 13:30:44 GMT
References: <1990Sep16.194605.11968@ecn.purdue.edu>
Reply-To: md89mch@cc.brunel.ac.uk (Martin Howe)
Followup-To: comp.sys.intel
Distribution: comp
Organization: Dept. of Elec. Eng. & Electronics, Brunel Univ., Uxbridge, UK
Lines: 41

In article <1990Sep16.194605.11968@ecn.purdue.edu> tlhilde@ecn.purdue.edu (Troy Hildebrand) writes:

>Can anybody help me with the difference between a 80386 and a 80386sx?  
The SX is to the DX what the 8088 is to the 8086, that is it is the SAME
internal execution unit, but the external bus size is smaller in order
to be able to make cheaper systems from it, with about 40% loss of
performance (depending on cache hit rates).

CHIP NAME		8088    8086    386SX   386DX
**internal** CPU	8086	8086	386DX	386DX
Prefetch queue		4       6	?	 16	bytes
External Addr Bus	20	20	24	 32	bits
External Data Bus	8	16	16	 32	bits


>I have been warned _not_ to go with a 386sx when purchasing a computer,
>no matter what the cost difference is.  What exactly is the difference
>between an 386 based motherboard and an 386sx motherboard?  This is in 
>regards to third party motherboards.  Are there any particular features
>which distinguish the 386 and 386sx boards?  

The SX motherboards are pretty much the same as DXs, performance-wise, *if*
they're ISA BUS (16-bits) based; a 386DX running over ISA bus is approx ==
to an SX, except when running out of any 32-bit memory installed on the CPU
local bus. On an EISA or PS2 bus, a 386DX will win easily, unless the menory
speed is lousy or the cache is badly implemented.  Also, the max. SX chip
speed is 20MHz and that's unofficial at the moment. The DX can be obtained
up to 33MHz. Again, this means nil over the ISA bus, which is the limiting
factor in speed for I/O or AT-style memory cards.

Anyone making an EISA (32-bit) SX motherboard is likely to be off
his or her trolley. If you see one, tell me what the hell a 32-bit
motherboard does for an SX chip (:-).

Regards,
Martin
-- 
  -   /|  . . JCXZ ! MOVSB ! SGDT ! iAPX ! | "Good morning Citizens. I would
  \`O.O' .    Martin Howe, Microelectronics|  remind you that Armed Robbery
  ={___}=     System Design MSc, Brunel U. |  is illegal in Megacity One." - JD
   ` U '      Any unattributed opinions are mine -- Brunel U. can't afford them.