Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!cs.utexas.edu!uunet!crdgw1!crdos1!davidsen
From: davidsen@crdos1.crd.ge.COM (Wm E Davidsen Jr)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 386SX replacements for 80286 machines
Keywords: 386SX motherboard questions.
Message-ID: <1541@crdos1.crd.ge.COM>
Date: 3 Nov 89 15:55:56 GMT
References: <786@awdprime.UUCP> <1989Nov2.080213.2989@ico.isc.com> <4521@utastro.UUCP>
Reply-To: davidsen@crdos1.UUCP (bill davidsen)
Organization: GE Corp R&D Center
Lines: 51

In article <4521@utastro.UUCP>, hgcjr@utastro.UUCP (Harold G. Corwin Jr.) writes:

|  I've been thinking of doing this myself.  Has anyone on the net actually
|  put a 386SX motherboard in an AT or a clone?  If so, would you be willing 
|  to comment on the project?  I am personally interested in the whole thing,
|  all the way from choosing a board and a dealer, through the actual mechanical
|  installation, to the moment of truth -- does it work as advertised or not?

  No big deal. Depending on how much stuff you have in there it can take
a long time. I did one with 2HD 2FD and a tape drive, 2S+3P, and it took
three hours total, most of which was spend uncabling and moving stuff.
Figure two hours for a more normal system. I put one (XT size) in an
original IBM portable (luggable). Both worked and more than doubled the
speed of the CPU. The portable got an EDSI controller and HH 160MB
drive, too, which probably helped more than the CPU.
|  
|  Particular questions of mine:  can the 120ns 256Kb RAM on the AT motherboard 
|  be used successfully on a new board, or should I plan on buying faster RAM?

  If you run 16MHz and 2w/s you can get away with it. It will not be
much faster than the 286 you take out. 100ns memory is <$100/MB, put in
what you need.

|  Similarly, what about my extended/expanded memory board with the same sort
|  of RAM?  The thought of replacing 2.5MB at today's costs for 80 or 100ns
|  RAM doesn't thrill me too much.  (I'm not particularly interested in speed, 
|  but mostly in the 386's memory management skills that are supposed to ease 
|  the problems of multitasking, working with large programs, data files, etc.)

  Since the SX is only 16 bit data, you don't lose on the bus, but you
will take a hit if you use slow memory. As VDISK it's okay, still a lot
faster than the disk, but if you execute in it, it's slow.

|  How about video cards and serial/parallel ports?  Can I use the ones I've got 
|  now, or will this be an added expense, too? (I'd like to keep my Hercules 
|  card until I have software that will use VGA.)  I know that I'll need a new 
|  hard/floppy controller, as well as a 387SX.

  The serial and parallel are so slow that you won't see a diference.
Saving 100ns of a device which cycles in ms is not worth money. The
387SX is a LOT faster than the 287, and you will like it if you do much
FP. The video depends on usage, for text it will be okay, for graphics
it will be slower than state of the art. State of the art costs a lot. I
have a rack of old superEGA and VGA boards I've pulled out looking for
better graphics. If you don't need it, don't spend money on it.

-- 
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