NetNews Usenet Archive 1992 #19/NN_1992_19.iso/spool/comp/sys/ibm/pc/hardware/23025

Internet Message Format | 1992-08-31 | 1.8 KB

Path: sparky!uunet!noc.near.net!mars.caps.maine.edu!maine.maine.edu!ree700a
Organization: University of Maine System
Date: Monday, 31 Aug 1992 10:33:20 EDT
From: <[e-mail]>
Message-ID: <[e-mail]>
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: 486 DX vs DX2: What's the difference ?
References:  <[e-mail]>
Lines: 23

  The MHz rating of either the DX or the DX2 chips is the speed at which
data is handled internal to the chip.  Thus, both 50MHz DX and DX2 run
at the same speed, given that all of the data they need is in the internal
8K cache <yeah, right!>.
  On the same motherboard (not local bus), they handle I/O, such as disk,
video, serial, parallel and ethernet at the same rate <slowly>.
  So, the difference is in how fast items may be brought from main memory
to the internal cache.  This is heavilly influenced by the speed and
structure of the memory and cache system.  Consider a system with zero
(effective) wait state RAM (e.g. 4-way interleaved 60 nS SIMMs and 15 nS
cache on a DX 50)...  Let this memory speed be a reference.  The DX2 uses
an external clock speed of one-half the internal speed.  Thus, for what is
effectively a 25MHz memory system (and hence cheaper!) you get half the
memory throughput.
  OK, you ask why the I/O, which is external, runs the same?  Other than
local bus, show me a system with even a 25MHz AT bus!
  So, what is the performance ratio?  Rather depends on what you do.  Most
PC systems are I/O bound anyways... no loss there.  Some applications are
CPU bound...  no loss there.  So, unless your application is memory bound,
you might never know whether it was a DX or DX2!  Benchmarks run anywhere
from 50% to 90% performance ratio of a DX2 to a DX...

   Jeff Andle