Subject: Re: pc164/ncr scsi problems
To: Ross Harvey <>
From: Brett Lymn <>
List: port-alpha
Date: 08/30/1999 10:42:26
According to Ross Harvey:
>I hate to sound like a broken record, but 4 drives is really too many for
>a singled-ended chain, especially if any of them are external.

4? Hell, the thing had 5 devices on it - one was external (external
cd, old drive 1, old drive 2, new drive, new cdrom).  I _knew_ I was
pushing the limits and I expected problems which is why I did not log
a PR.  The whole purpose of me getting the new stuff was to get rid of
the 3 hard disks that were on the chain and replace it with something
more capacious in a single device (you ever tried shoe horning two
full height drives, a qic tape & 2 floppies into a PC tower case? :-)

>(How long was the cable, all total?)

Hmmm internal is about 1.5m-2.0m, add another .5m for external.

> What's also
>important, for pushing the limits like this, is to avoid PVC and other
>hi-dielectric-constant cables.  You want an e(r) < 3 and preferably around
>2, and low-skew cable construction.

I am not sure what the cable I have is made from.  I scrounged it from
work, like I said it is twisted pair ribbon cable - pairs of wires are
twisted together and the pairs welded to a plastic sheet.  Means I get
a signal/ground twisted pair for each signal :-)

>  Of course, if you went differential
>you could use the cheapest cable and random garbage terminators and everything
>would be fine.

And you can run it for much longer.  I am almost tempted to get a
fast, wide diffential controller since there are some 2Gig FWD disks
that may be coming spare here :-)  The only problem is lack of pci
slots :-(

Brett Lymn, Computer Systems Administrator, British Aerospace Australia