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From: jones@acsu.buffalo.edu (terry a jones)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Why buy a DX over an SX?
Message-ID: <72386@eerie.acsu.Buffalo.EDU>
Date: 22 Apr 91 20:11:31 GMT
References: <14534@encore.Encore.COM> <1991Apr12.162615.13529@holos0.uucp> <1991Apr21.203004.9909@unlv.edu>
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In article <1991Apr21.203004.9909@unlv.edu> whitney@reed.cs.unlv.edu (Lee Whitney) writes:
>In article <1991Apr12.162615.13529@holos0.uucp>, lbr@holos0.uucp (Len Reed) writes:
>) 
>) So what?  You're running *all* 16-bit software and you want to know
>) why having a a 32-bit data path doesn't buy you much?  Windows puts
>) the machine into proctected mode, but it doesn't use 32 bit mode.
>) 
>Your statement is impratical and misleading.  First, the 386SX DOES have 
>a 32 bit data path or else it would not be a 386!  It's bandwidth is only 
>limited across the bus, and since 90% of 386 buses are 16 bit (ISA), most DX 
>systems would not realize a tremendous advantage over SX's when using 
>32-bit protected mode software.
>
>A $200 cache may be worth a 25-30% performance increase, but the 5-10% 
>increase of a DX over an SX with a 16 bit bus is probably not.

	You are also confusing the issue somewhat.  The 80386DX system will
no doubt have a 32bit wide memory bus.  Granted, the ISA bus is only 16 bit,
but that is a real good reason not to hang memory out there in the form of
an expansion card.  Put it all on the motherboard if at all possible.  This
memory bus is separate and very different than the ISA bus.  In the case
of the 80386SX, the processor's memory accesses are 16 bits wide, period.
So the memory bandwidth of the DX is much greater than that of the SX without
even considering the cache benefits.  It really is a matter of cost, if you 
have the money to spend, and are concerned about performance or are going
to run Unix, etc., go with the DX.  If you are on a budget, go with the SX.
The SX system will be cheaper since the cost of the CPU is lower, and the
cost of the motherboard will be cheaper since they only have to implement
the 16bit wide memory bus.


	Terry



Terry Jones   				{rutgers,uunet}!acsu.buffalo.edu!jones
SUNY at Buffalo ECE Dept.	  or: rutgers!ub!jones, jones@acsu.buffalo.edu




-- 
Terry Jones   				{rutgers,uunet}!acsu.buffalo.edu!jones
SUNY at Buffalo ECE Dept.	  or: rutgers!ub!jones, jones@acsu.buffalo.edu