Path: utzoo!attcan!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!uunet!crdgw1!crdos1!davidsen
From: davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr)
Newsgroups: comp.sys.ibm.pc
Subject: Re: WANTED: info on 386-25 system board replacements
Message-ID: <1564@crdos1.crd.ge.COM>
Date: 7 Nov 89 14:10:49 GMT
References: <4548@cbnewsc.ATT.COM>
Reply-To: davidsen@crdos1.UUCP (bill davidsen)
Organization: GE Corp R&D Center
Lines: 72

wolfordj@cbnewsc.ATT.COM (j.w.wolford) writes:
|  1 - Processor and chips marked at rated speed (ie not 20Mhz parts at 25Mhz)

  I have the same feeling, although I have never seen a DX part which
wouldn't run 25MHz.

|  2 - Coprocessor slot for 80287/80387 (ok if it has Weitek, but I won't use it
|  	287 for now because a 387 is $450-500... and I don't need anything
|  	faster than a 10Mhz 287 for now (that does not mean I don't want a 387)

  This is a lousy economy. The 10MHz 287 will be about $200, the 25 MHz
387 about $450 (from _PC Week_ ads). The 387 will be about 10x faster.
If you have a real need for for a coprocessor buy the 387. The Weitek is
a lot more money (you have to buy a compiler which uses it, too). I have
a 10MHz 287 in my home system because I couldn't get a 387 in 1986, but
I regret it every time I do something f.p. intensive.

|  3 - Bus speed, for a 386's this usually 8Mhz... but

  Faster than 8MHz may give trouble with some boards. I would NOT buy a
machine which didn't offer the option of 8MHz operation, although you
can get some minor performance gains from a faster bus. The only thing
which really shows the gain is video, since disk, tape, serial and
parallel are all slower than the 8MHz bus.
|  4 - Being able to enable/disable shadow RAM... Have heard problems with
|  	this with non-DOS operating systems

  You may lose 384k with UNIX or OS/2. Never heard of an operational
problem, and even if you turn off shadowing you may not get the 384k back.

|  5 - System board memory...amount, speed, type (DIP, SIMM, SIPP), 256K, 1M
|  	anywhere from 4MB to 8MB maxed.

  If you get a system which will go 8MB on the sysbd you will not have
to buy an extension board for quite a while.

|  6 - 32bit wide memory bus slot... again, amount and type
|  	2-8MB per board.

  See 5.

|  7 - BIOS - AMI requested for configuration capability... Pheonix and Award
|  	acceptable.

|  8 - Cache....NOT required...32K, 64K, or 128K... Almost doubles the cost
|  	of the board... is a cache worth that much (I feel its mostly
|  	marketing hype... it helps, maybe ~20% over a interleaving system.

  cache can make a big difference for some operations in video memory
(if you are reading back for some reason). I don't see any indication
that it doubles the price of the board, dealer price goes up about $200.
Some of the cached boards are very pricy, but that's brand name, not
manufacturing cost (see my earlier posting about this).

|  9 - Number of layers - 6 min, 8 is better for noise.

  I guess... good layout is far more improtant than # of layers for both
noise and RF emission.

|  10- Chipset vs descrete....286 everyone uses a chip-set, but for a 386
|  	this does not seem as clear cut if one is better than the other.

  Generally the fewer connects the less failures. Since this is a
statistical thing, it doesn't apply to any single machine, but I feel
better about low part counts, if only because they allow the board
design to concentrate on noise rather than getting all those connections
in there.
-- 
bill davidsen	(davidsen@crdos1.crd.GE.COM -or- uunet!crdgw1!crdos1!davidsen)
"The world is filled with fools. They blindly follow their so-called
'reason' in the face of the church and common sense. Any fool can see
that the world is flat!" - anon