486 DX vs DX2: What's the difference ?

[e...@dstos3.dsto.gov.au]

486DX Vs 486DX2: What's the difference

Sorry if this is an FAQ but I've scoured this news group to no avail.
Can anyone explain the difference between the DX and newer DX2 chips?

Much Appreciated
Themie Gouthas

[REE...@maine.maine.edu]

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

[Joel Ross]

From jross Mon Aug 31 12:14:09 1992
To: /afs/acpub/users6/jross/.article

I would like any advice available on controller cards for RLL (for an ST
238R drive specifically) that can be configured as the secondary drive in an
AT clone that already has an IDE drive.

Thanks in advance,

Joel Ross

[Michael Nolan]

<REE...@MAINE.MAINE.EDU> writes:

> 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...

So, which is better: a 50Mhz DX2 or a 33Mhz DX? (Yeah, I know, it depends.)
And this is NOT an academic question, these kinds of systems are showing up
in the discount stores for roughly the same $$. What you are saying would
seem to say that most of the time the 50Mhz DX2 will beat the 33Mhz DX,
right?
---
Michael Nolan, no...@tssi.com "Freedom of the press is still alive in
Tailored Software Services, Inc. America, at the U. S. Mint" (Gallagher)
Lincoln, Nebraska (402) 423-1490

[t...@gibdo.engr.washington.edu]

This is what PC magazine says in its review of 63 DX2/50 systems
in a box entitled "DX2 vs. OverDrive: Do You Want Your Speed Boost
Now or Later?"

"Does the OverDrive chip give true 50-MHz 486DX performance?
No, but it's close. Intel claims 1.8 times the performance
of a 25-MHz 486. This coincides with the performance of
factory installed DX2s seen in this roundup, which performed
at 96 [sic: they meant 92] percent the speed of a true 50-MHz
486DX on PC Magazine Labs' processor benchmark test."

This 92 percent figure roughly matched what I figured for my own
486DX2/50 from GW2000. The performance turns out to be BETTER
than any of us were expecting and luckily the prices won't go
back *up* because of it. The trick seems to be in the cache size.
Under "What the Numbers Mean: 486 DX2 PCs" they state:

"Considering only those DX2s that feature at least a 128K
cache we found that the average DX2/50 performed at 96
percent of the speed of the average DX/50 (505 versus 525
operations per second)...

The average memory performance for all the DX2s was 6,314
KBps (compared with 8,017 KBps for the DX/50s)--78% of the
performance of true 50-MHz systems....

The reasonable conclusion: Under most applications, PCs
utilizing the clock-doubler technology should perform
nearly on the same level as a true 50-MHz 486 when the
DX2 chip used with an appropriately designed external
cache. Memory intensive work will suffer, since memory
accesses leave that fast 50-MHz world inside the CPU
and venture onto the memory bus at 25MHz."

So there you have it. Hope this helps. (BTW: Occidental's 486DX2/50
(with 8MB RAM, 240MB 12ms IDE hard drive, one (of eight) local bus
slots, and SAME DAY SHIPPING) looks pretty good at $2495 depending on
the video card they're using (The ad doesn't say what it is.).

-- Tad Perry Internet: t...@gibdo.engr.washington.edu
CompuServe: 70402,3020
NIFTY-Serve: GBG01266

[John Manning]

In article <1992Sep1.0...@u.washington.edu>, t...@gibdo.engr.washington.edu writes...

I took advantage of Occidental's faxback service to get specs on their
offerings. The only bad thing(and this is a matter of perspective) is that
their 240MB HD is a Seagate.

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| John Manning | Opinions expressed are my own. |
| j_ma...@csc32.enet.dec.com | I do not represent Digital Equip. |
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