Memory requirements for 386/ix

[John G. De Armond]

In article <710 at ncs.dnd.ca> marwood at ncs.dnd.ca (Gordon Marwood) writes:
>We will shortly be installing 386/ix for the first time (on a
>Honeywell-Bull 386).  The recommended minimum memory is 2MB.  I would be
>interested to hear about recommendations for memory size, and its
>practical effect on performance of 386/ix.  I realize that this depends
>a lot on the way in which the machine is used.  All I can say about our
>projected use is that it will be used for mail by a group of, perhaps 20
>people, though I suspect no more than 6 at a time.  We also expect to
>use it as a file server for the same group, using NFS.  I suppose that
>the closest comparison might be with someone who has used 386/ix on a
>similar machine (20 MHz) for a similar group size.


Don't even think of starting with less than 8 MB for a group that size.
I've run 386/ix with 2, 4, and 8 meg and the transformation at each
stage is awsom.  This machine is used for development by 2 people, news
reading by a few more and handles a very heavy news redistribution load.
With 2 people logged in and any kind of news processing going on in the
background, the 4 MB machine paged rather badly.  When we upgraded to 
8 meg, the personality of the machine changed markedly.  Even when the
system is not paging, it is much more responsive.

Note:  I have done no tuning on this system.  The kernal is configured 
exactly as shipped and/or as kconfig builds it.  

With 20 users I presume you are connecting these in through an Ethernet?
I hope so.  4 or 5 users on TTY logins is pushing it pretty far on this
20 mhz machine.  If you are installing Ethernet, you must use an intelligent
card such as the Interlan unit supported by ISC.  I've used this card and
can report that it performs very well.  In general, you want to avoid
creating interrupts on the PC bus.  I've determined that it is almost 
essential to have intelligence in anything that handles a datastream.

The configuration here is a no-name klone 20 mhz 386 with 8 mb of 80 ns
RAM running 0 wait state.  The drive controller is an Adaptec 1272 SCSI
adaptor with floppy interface (Recommended!).  Video is a mono graphics
board (slow).  Serial interfaces consist of an 8 port intelligent card
from StarGate (highly recommended) and a single PC-type async card with
a 16550 uart (mandatory!)  Hard drive configuration is a high speed
CDC Wren 40 meg drive for the root partition and 2 380 MB Newbury
Data SCSI drives (Trash, but cheap at the time.)  The Wren is run from
a fast ST-506 AT controller.  Tape backup is a Wangtek 60 mb unit.  Slow
but reliable.

I HIGHLY recommend a separate drive for the root partition.  I spent
many miserable days reinstalling from floppies after one disk problem
or the other before I put a stone cold reliable root drive on the system.
Unless you have at least 2 physical drives, almost any reconfiguration 
of the file system mandates going back to floppies.

One further comment on the Stargate board.  This board and the company 
behind it has been fantastic.  I have an older 8 bit interface version,
though they make a 16 bit interface one.  With the performance I've
seen, I really can't imagine a pressing need for the 16 bit one.  My
initial test of the board consisted of setting up 8 simultaneous
cats of a large file to each of the 8 ports at 38.4 kilobaud.  SAR 
reported a CPU idle time of 98%!  I verified with a protocol analyzer
that the pipe was being kept full on all ports.  In practical use,
I can now force handshaking on all my Telebit feeds downstream even one
using the Bell smart card.  I run zmodem transfers at 38.4 kb between 
a PC and the system with no problems at all.  

The installation went perfect.  Set a couple of dip switches on the board
and tell the installation script these settings and let it rebuild
a kernal.  I called tech support with a minor question (800 number)
and was serviced by a very knowledgable person who helped me immediately.

An additional note.  The manual documents how to write applications
to run on the 80186 coprocessor on the board.  The firmware is loaded
as pump code when you go to run state 2.  Since the board uses Z80 SIO
equivelents and since each port has full modem control and all handshake
lines, all kinds of communications processing applications ideas arise.
At the least, one could program the thing to answer the phone and output
a "system down" message when dialin is not available.

One should also note that this board can be run in polled mode if you
don't have a spare interrupt.  I tried it polled and found performance
to be below that of interrupt-driven service.  I suspect tuning would
solve that problem but since I had a spare interrupt, I just flipped
a switch.  One thing I noted in the manual is that all shared memory
mapping is done by  the pump code and that multiple boards can 
share the same shared memory segment.  Very nice when high memory segments
are getting tight as in my system.

My only complaints are that the manuals are fairly poor, with the Unix
section being an addendum to the DOS/Generic version and the fact that
they charge $50.00 for additional system drivers.  If you wanna use it 
on Xenix or DOS too, that's extra money.  Minor quibbles.

I didn't mean for this to turn into a Stargate commercial but it's 
so rare to run into quality support in the PC Unix field, I thought
a positive note for a change would be welcome.

BTW, after working with Stargate and their vendor-supported driver, I'm
suddenly glad that Interactive is shoving driver support off to the 
vendors.  Knowledgable service is refreshing.

John

-- 
John De Armond, WD4OQC                     | The Fano Factor - 
Radiation Systems, Inc.     Atlanta, GA    | Where Theory meets Reality.
emory!rsiatl!jgd          **I am the NRA** |