I'm using a Asus A8N-SLI motherboard that has two PCIx-16 slots that
can accomodate two graphics cards in tandem. However, I need to use
only one of these slots to accomodate my graphics card. I'd like to
use the other PCI-x slot for a legacy 3.5v SCSI card.

I understand that PCIx slots are backward compatible as long as the
card is 3.5v. However, the slot is positioned at a greater distance
from the rear of the computer than the other plain PCI slots, and so
there seems to be a mechanical incompatibility.

Is that second slot usable for 3.5v SCSI adapter even though it is a
SLI motherboard that assumes it will be used for a graphics card?

If so, Will the presence of a slower SCSI adapter in one slot degrade
the performance of the graphics card in the other?

The alternative would be to purchase a PCIx SCSI adapter, but those
I've seen have been very expensive. If I must use a PCIx SCSI adapter
card, are there any available that may be slow, but are reliable and
inexpensive?

A bit OT, but the reason for my question is that the motherboard has
three conventional PCI slots that are being used by a sound card, NIC,
and U320 SCSI adapter. There are slow internal and external SCSI
devices I'd like to add without degrading the U320 SCSI bus, and hence
my question. I gather that it is best not to use the onboard NIC (I'm
running Linux), and I plan to make special demands on the sound card
which the onboard sound chip may not support (to digitalize analog
inputs that involve some RF).

--

Haines Brown
KB1GRM

In message <87psp71ofc.fsf (AT) teufel (DOT) hartford-hwp.com>, Haines Brown
<brownh (AT) teufel (DOT) hartford-hwp.com> writes

--
Jeremy Boden

Previously Haines Brown <brownh (AT) teufel (DOT) hartford-hwp.com> wrote:
These are PCI-E and not PCI-X. PCI-E is not backwards compatible to
PCI/PCI-X. It has an entierely different bus concept with serial
lanes, while PCI(-X) use a paralell bus layout. And yes, you can put
normal PCI cards in PCI-X slots, at least for the PIC-X 66MHz/64bit
slots I have in a server mainboard it works both electrically and
mechanically. But as I said yu don't have these.

Arno

Arno,

Thanks for the reply. I had assumed in my ignorance, that "X" and "E"
were just different ways to say "Express." My current SCSI adapter is
an Adaptec 29320. My experience is that attaching a vintage device to
it (external connection to a HP ScanJet IIcx) resulted in I/O errors
(disasters a better word) at boot time, to say nothing of its effect
on my internal U320 HD performance.

--

Haines Brown
KB1GRM

Previously Haines Brown <brownh (AT) teufel (DOT) hartford-hwp.com> wrote:
Don't blame yourself, I thought the same until I read a detailed
technical description.

Incorrect termination? SCSI is very reliably if the cabeling and
termination is done right. If done wrong, it shows symptoms as
the ones you describe. Also the differential bus (LVD) goes back to
single-ended (SE) when one or more targets do not support
differential signals. That also means lower speed. Maybe that is
the problem? Best connect the scanner to its own contoller or get a
controller that has a dedicated SE channel for external devices.
Might be cheaper to get a comparable USB scanner though.

Arno

In message <3tkm5vFspnrcU1 (AT) individual (DOT) net>, Arno Wagner <me (AT) privacy (DOT) net>
writes
Your 29320 has an internal 50 pin SE connector which could be used with
a "breakout connector" for your scanner, thereby isolating your HD's
from scanner problems. It is also a 64 bit device and should be happy in
PCI-X.

--
Jeremy Boden

Arno Wagner <me (AT) privacy (DOT) net> writes:

Your question caused me to look and sure enough, no termination. A
termination is sitting there (connected to a DB-25 on the scanner),
but the cable is instead connected unterminated to another connector,
a Centronics 50-pin. The new SCSI U320 SCSI adapter I'm using has what
I guess is a microD-50 connection, and the only cable I had handy for
that terminated in a Centronics, and I must have at one point
carelessly plugged it in where it fit rather than think about the
termination.

I finally found advertised (Newark) a Centronics-Centronics
termination, which would be a lot cheaper than buying a USB
scanner. I'll give it a try, for I've got no spare slot for an
additional SCSI adapter.

Thanks.

--

Haines Brown
KB1GRM

Previously Haines Brown <brownh (AT) teufel (DOT) hartford-hwp.com> wrote:
O.k., so you have termination (the second connector is for daisy-chain
or terminator), but only on the lower 8 bits. Still, if the external
connector is 8 bit SCSI, the terminator should be o.k.. I think thet
the external bus is a separate 8 bit SCSI bus, in which cases it needs
to be terminated at both ends, i.e. at the scanner (which you seem to
have) and on the card. If the card also has an internal 8 bit scsi
connector, then it will have termination in the card for the 8 bit bus
optionally but not mandatorily. Check whether the card has termination
for the 8 bit SCSI bus turned on. Could be in the Card's BIOS, could
also be a switch or a resistor array on the card.

That thing will do the same as the terminator on the second scanner
connector, so it should not help. Sorry.

Arno

Arno Wagner <me (AT) privacy (DOT) net> writes:

Thanks. I thought I was being careless, but in fact I knew what I was
doing ;-)

Unfortunately, my datasheet for the Adaptec 29320 says it is "single
channel", which I assume means a single bus, and so a slow external
device will degrade performance on an internal U320 hard disk. In any
case, what would be a good way to measure relative bus transfer speed?

Also, I gather that if I terminate my LVD Ultra320 (or Ultra2) bus
with an old Ultra SCSI termination, I could be in trouble.

A very elementary question. The adapter's single internal connector is
described as "68-pin internal LVD/SE" and the external connector as
"68-pin LVD/VHDCI". Can I infer from that description the bus
bandwidth? I know that 80-pin means that the device connected would be
self-powered, but does the difference between 50-pin and 68-pin imply
something about the bit width of the bus?

Why I ask is because my scanner cable is VHDCI 68-pin at the computer
end, and Centronics-50 at the scanner end. Does use of this cable
require the enabling of 8-bit termination for the bus in the
adapter's BIOS? If, as I suspect, adapter does not support this (can't
reboot to the adapter's BIOS set up at the moment), the use of the
scanner with this adapter would seem impossible.

The adapter manual I says I must use a proper Ultra320/160 or Ultra2
cable and terminator. Can I infer that my scanner is Ultra2 from the
fact that it has a Centronics-50 connector?

Unless I figure out how to add another SCSI adapter, I may have to buy
a USB scanner after all.

Incidentally (OT), my Asus A8N-SLI manual refers to the non-PCI
Express slots as simply "PCI". How would I know by inspecting them
whether they are 64-bit? The motherboard board itself does supports
64-bit architecture.

--

Haines Brown
KB1GRM

Previously Haines Brown <brownh (AT) teufel (DOT) hartford-hwp.com> wrote:
Correct. Part of the bus will be unterminated if you do that.

I don't think so.

I think you scanner is old enough to be just SE. I am sorry, but I don't
know whether the external connector supports that. May be that it does
not. Centronics-50 is used for SE as well, you cannot infer much from it.
I think you cannot terminate the external bus propperly with that
scanner attached.

The only remaining option I see is a Ultra2 or Ultra320/160 to SE
adapter on the scanner. May be expensive and will degrade performance.

I think you should do that.

Unlikely. But you can insert a PCI-X card into a PCI slot.
Not all of the connector will be inside the slot, but it should work
at reduced speed.

Arno