SCSI v USB Scanners?


J

John

Hello

A lot of people seem to recommend SCSI connected scanners over USB
ones, but isn't USB faster than SCSI?

Maybe I'm wrong but I thought the speeds for the two standards were as
follows:

USB2 480 Mbps
SCSI-3 Ultra 20 MBps

I thought that even USB 1 was 40 Mbps? So wouldn't that have been
faster than the latest SCSI-3 Ultras speed can muster?

Or perhaps the difference comes with the controllers and the SCSI just
has better controllers and drivers, and the USB takes up too much
resources? Or perhaps the USB can't achieve the top speeds it is
supposed to be capable of, but the SCSI can?

I'm a tad confused on this, but it does seem from what people say in
comp.periphs.scanners that SCSI is faster?

Thanks for any clarification on this

John
 
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M

Mac McDougald

Hello

A lot of people seem to recommend SCSI connected scanners over USB
ones, but isn't USB faster than SCSI?

Maybe I'm wrong but I thought the speeds for the two standards were as
follows:

USB2 480 Mbps
SCSI-3 Ultra 20 MBps

I thought that even USB 1 was 40 Mbps? So wouldn't that have been
faster than the latest SCSI-3 Ultras speed can muster?

Or perhaps the difference comes with the controllers and the SCSI just
has better controllers and drivers, and the USB takes up too much
resources? Or perhaps the USB can't achieve the top speeds it is
supposed to be capable of, but the SCSI can?

I'm a tad confused on this, but it does seem from what people say in
comp.periphs.scanners that SCSI is faster?

Thanks for any clarification on this

John
Think you have megaBITS (Mb) and megaBYTES (MB) mixed here.
Here's a pretty good chart of USB/SCSI/Firewire speeds:
http://www.macspeedzone.com/archive/5.0/de/gifs/firewirevsscsi.gif

Few if any consumer grade scanners made with SCSI interface now anyway,
so fairly moot, unless you're using older ones (like me)...


Mac
 
D

David Littlewood

Mac McDougald said:
Think you have megaBITS (Mb) and megaBYTES (MB) mixed here.
Here's a pretty good chart of USB/SCSI/Firewire speeds:
http://www.macspeedzone.com/archive/5.0/de/gifs/firewirevsscsi.gif

Few if any consumer grade scanners made with SCSI interface now anyway,
so fairly moot, unless you're using older ones (like me)...
The really important difference IMO is that SCSI peripherals are an
utter pain in the backside to get working (and the pain increases as a
high power of the number you daisy-chain), whereas every USB device I
have ever used has connected and worked first time right out of the box.
 
J

Julian Knight

From John on 02/Aug/2004 00:12:
Hello

A lot of people seem to recommend SCSI connected scanners over USB
ones, but isn't USB faster than SCSI?

Maybe I'm wrong but I thought the speeds for the two standards were as
follows:

USB2 480 Mbps
SCSI-3 Ultra 20 MBps

I thought that even USB 1 was 40 Mbps? So wouldn't that have been
faster than the latest SCSI-3 Ultras speed can muster?

Or perhaps the difference comes with the controllers and the SCSI just
has better controllers and drivers, and the USB takes up too much
resources? Or perhaps the USB can't achieve the top speeds it is
supposed to be capable of, but the SCSI can?

I'm a tad confused on this, but it does seem from what people say in
comp.periphs.scanners that SCSI is faster?

Thanks for any clarification on this

John
Don't forget that to achieve 480Mbps, USB has to make very heavy use of the PC's
CPU unlike SCSI and Firewire. This is probably OK for scanning but often
catches people out for Video and other more intensive work.
 
J

Julian Knight

From Mac McDougald on 02/Aug/2004 00:55:
Think you have megaBITS (Mb) and megaBYTES (MB) mixed here.
Here's a pretty good chart of USB/SCSI/Firewire speeds:
http://www.macspeedzone.com/archive/5.0/de/gifs/firewirevsscsi.gif

Few if any consumer grade scanners made with SCSI interface now anyway,
so fairly moot, unless you're using older ones (like me)...


Mac
Anyone had any joy with a SCSI->USB converter? I currently only have an ISA SCSI
card which doesn't fit in my newer computers and was thinking this would be the
best bet (avoiding the PCI/PCI Express/... issues altogether!).
 
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G

Glenn

Julian said:
From John on 02/Aug/2004 00:12:

Don't forget that to achieve 480Mbps, USB has to make very heavy use of
the PC's CPU unlike SCSI and Firewire. This is probably OK for scanning
but often catches people out for Video and other more intensive work.
USB definately uses a lot of CPU power. When I have my USB scanner
driver GUI opened, CPU usage is 50% and CPU temps jump to about 50 C.

Julian, are you looking for a PCI SCSI card? I have one just sitting
here. I used it for optical drives, but I have gone IDE. I haven't
used it since August 2002, I assume it works, it's been boxed up since then.
 
T

Thor

Don't forget that to achieve 480Mbps, USB has to make very heavy use of
USB definately uses a lot of CPU power. When I have my USB scanner
driver GUI opened, CPU usage is 50% and CPU temps jump to about 50 C.
I think much depends on the USB chipset in particular, not necessarily the
spec. I just transferred a 500MB file from my external hi-speed USB 2.0
harddrive to my local harddrive, and my CPU utilization averaged around
15-18% throughout. I'm using a USB 2.0 interface card with an NEC controller
chip.
 
D

David R

David Littlewood said:
The really important difference IMO is that SCSI peripherals are an
utter pain in the backside to get working (and the pain increases as a
high power of the number you daisy-chain), whereas every USB device I
have ever used has connected and worked first time right out of the box.
I have never had any problems with SCSI devices. My experiences have
found them to be fast, reliable, and easy to configure. I've had
drives and scanners running from Windows 98 to Windows XP.
 
D

David Littlewood

David R said:
I have never had any problems with SCSI devices. My experiences have
found them to be fast, reliable, and easy to configure. I've had
drives and scanners running from Windows 98 to Windows XP.
That's great; I wish you could share your secret. I have rarely been
able to get two devices to work on the same chain, whatever combination
of terminators/no terminators, permutations of device numbers etc. I
tried.

Life is too short to waste on stuff like that...
 
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R

RSD99

SCSI is really quite easy to set up.

(1) Put terminations on both of the *physical* ends of the transmission line(s). ONLY two
terminations, one on each end. Usually, that will be (a) the adapter card, and (b) the
last device on the chain. HOWEVER, if there are two cables coming out of the adapter, the
adapter card should be unterminated, and the last device on each cable should be
terminated.

(2) Device #7 is the adapter card in the PC ... do not assign anything else to that number

(3) EACH device on the SCSI chain needs a unique device number, make sure that there are
no duplicated. That leaves Device numbers 0, 1, 2, 3, 4, 5, 6, and 7 for your devices. If
you are setting up devices such as a scanner, try to steer clear of 0 and 1, which are
normally used for disk drives.

(4) If you are installing Hard Disks, 'Device 0' will be the boot drive.
 
D

Dances With Crows

[ alt.computer removed ]
["Followup-To:" header set to comp.periphs.scanners.]
That's great; I wish you could share your secret.
It probably involves goats and blood sacrifices. SCSI cards, like
certain Elder Deities, must be placated properly.
I have rarely been able to get two devices to work on the same chain,
whatever combination of terminators/no terminators
Um? No terminators = no workee. A SCSI bus must be terminated at both
ends of the bus, and *only* at both ends, not in the middle. Many SCSI
cards have "auto-termination", which can be turned on in the card's BIOS
or with a jumper on the card. You typically want to set that to "on"
unless you have both external and internal SCSI devices.

Then connect your SCSI devices, daisy-chaining them from the card's
ports. Each SCSI device must have a SCSI ID ranging from 0 to 6 (or 0
to 15) and in a chain, no 2 devices can have the same ID. IDs are
settable with jumpers or with buttons on the devices; check your
devices' manuals for info. The SCSI card itself almost always takes ID
7.

Terminate the bus. Make sure you use 2 terminators if you have both
external and internal devices. Make sure you use the proper
terminators; if you mix 68-pin and 50-pin devices on a chain, you need
to use 68-pin terminators or your 68-pin devices won't work.
permutations of device numbers etc. I tried.
I've never had to troubleshoot SCSI problems on 'Doze, only Linux. How
would you do the equivalent of "grep -i SCSI /var/log/messages" on
'Doze, anyway? Also, remember that some SCSI scanners were sold with
cut-rate SCSI cards that only supported a subset of the SCSI protocol.
These cards typically refused to work with peripherals other than the
scanners they were shipped with. If you really want help with your SCSI
problems, give a detailed description of your SCSI bus and the makes and
model#s of every periperal including the SCSI card that's attached to
it.
Life is too short to waste on stuff like that...
SCSI is very nice when it works properly, and it's practically essential
for any medium-to-high-end operation. It's probably too complicated for
Joe User though, what with termination and IDs and the lack of decent
diagnostics for things like "bus not terminated on one end" and goats.
Now, if it were only possible to get USB2/Firewire tape drives....
 
D

David Littlewood

RSD99 said:
SCSI is really quite easy to set up.

(1) Put terminations on both of the *physical* ends of the transmission
line(s). ONLY two
terminations, one on each end. Usually, that will be (a) the adapter
card, and (b) the
last device on the chain. HOWEVER, if there are two cables coming out
of the adapter, the
adapter card should be unterminated, and the last device on each cable
should be
terminated.

(2) Device #7 is the adapter card in the PC ... do not assign anything
else to that number

(3) EACH device on the SCSI chain needs a unique device number, make
sure that there are
no duplicated. That leaves Device numbers 0, 1, 2, 3, 4, 5, 6, and 7
for your devices. If
you are setting up devices such as a scanner, try to steer clear of 0
and 1, which are
normally used for disk drives.

(4) If you are installing Hard Disks, 'Device 0' will be the boot drive.
Did all this, in every permutation, with two different SCSI cards.

I know quite a few other people who also find them a PITA.
 
D

David Littlewood

[ alt.computer removed ]
["Followup-To:" header set to comp.periphs.scanners.]
That's great; I wish you could share your secret.
It probably involves goats and blood sacrifices. SCSI cards, like
certain Elder Deities, must be placated properly.
I have rarely been able to get two devices to work on the same chain,
whatever combination of terminators/no terminators
Um? No terminators = no workee. A SCSI bus must be terminated at both
ends of the bus, and *only* at both ends, not in the middle. Many SCSI
cards have "auto-termination", which can be turned on in the card's BIOS
or with a jumper on the card. You typically want to set that to "on"
unless you have both external and internal SCSI devices.
The reason I mentioned "no terminators" is that (IIRC - it was a couple
of years ago) one of the devices had a built-in switchable terminator.
Then connect your SCSI devices, daisy-chaining them from the card's
ports. Each SCSI device must have a SCSI ID ranging from 0 to 6 (or 0
to 15) and in a chain, no 2 devices can have the same ID. IDs are
settable with jumpers or with buttons on the devices; check your
devices' manuals for info. The SCSI card itself almost always takes ID
7.
Done.

Terminate the bus. Make sure you use 2 terminators if you have both
external and internal devices. Make sure you use the proper
terminators; if you mix 68-pin and 50-pin devices on a chain, you need
to use 68-pin terminators or your 68-pin devices won't work.
Now that last point ^is^ new to me - and just could be why I had so much
trouble. Problem is it was, as I say, a couple of years ago, but I could
just possibly have been using a 50-pin terminator with a 68-pin scanner
in the middle. Why do they never tell you these things?
I've never had to troubleshoot SCSI problems on 'Doze, only Linux. How
would you do the equivalent of "grep -i SCSI /var/log/messages" on
'Doze, anyway? Also, remember that some SCSI scanners were sold with
cut-rate SCSI cards that only supported a subset of the SCSI protocol.
These cards typically refused to work with peripherals other than the
scanners they were shipped with.
Funnily enough, the only* trouble free SCSI use I had was with one of
these that shipped with a Umax scanner about 6-7 years ago. Things only
got bolloxed up when I got another SCSI device and had to use a grown-up
card.

*Actually, truth be told, I think I also had some good experiences with
a PCMCIA card in a laptop, at least when only using one device.

If you really want help with your SCSI
problems, give a detailed description of your SCSI bus and the makes and
model#s of every periperal including the SCSI card that's attached to
it.
Thanks for the kind offer, but I gave up on it and bought new and much
better) stuff that uses USB. Don't care how much system power it uses,
it scans fast and trouble free! Gave the old stuff (including cards) to
my daughter a couple of weeks ago to see if she and her boyfriend can
make it work. Maybe they know the right kind of goats...
SCSI is very nice when it works properly, and it's practically essential
for any medium-to-high-end operation. It's probably too complicated for
Joe User though, what with termination and IDs and the lack of decent
diagnostics for things like "bus not terminated on one end" and goats.
Now, if it were only possible to get USB2/Firewire tape drives....
I guess I should have gone to Hogwarts.

Thanks for the help anyway.
 
R

R. P.

David Littlewood said:
Funnily enough, the only* trouble free SCSI use I had was with one of
these that shipped with a Umax scanner about 6-7 years ago. Things only
got bolloxed up when I got another SCSI device and had to use a grown-up
card.
That Umax SCSI cards was the DMX (DoMeX) model, right? I've been
trying to configure my Umax 2200 with a Tekram DC-390 U2W card to no
avail, despite the DC-390 being listed on the Umax Web site as being
compatible with this scanner. However, it looks as if the Umax SCSI
installation method is still installing the DMX drivers which are
probably the reason I have trouble making it run with my SCSI adapter.
Unfortunately Umax support by email is not very helpful. They only
responded to my first email and mostly were trying to steer me to the
use of the USB interface which this scanner also has. But I bought this
scanner mainly for its SCSI interface as I run a totally SCSI system and
quite trouble-free for a long time. Plus SCSI is much faster than
USB-1.

To those who might not know, this Tekram DC-390 U2W adapter is a pretty
interesting one, as if it was two cards in one, one of them operating a
wide U2W bus using 68-pin connectors, the other a narrow SCSI-2 bus with
50-pin connectors. So I run 3 SCSI-3 HDs on the wide bus at 80 MBS each,
with nothing connected to the external 68-pin connector. I run a
Pioneer SCSI DVD drive from the internal 50-pin connector and wanted to
use the scanner from the external 50-pin connector through a custom made
50-to-25 converter cable because the scanner uses two Apple type 25-pin
SCSI connectors (one in, the other out, in case of daisy chaining.) I,
of course terminated the other 25-pin connector with an active 25-pin
terminator. All but the scanner are sync devices, the scanner is async.
As far as I can see my setup works fine with the adapter as all the
devices are recognized on different IDs by the SCSI BIOS and all the
SCSI devices work fine until I try to scan something. Than the Umax
driver locks up the SCSI bus and my system freezes. Only hard reset
gets me out of it. Fortunately the XP file system integrity is
maintained and I can reboot. Actually, if I reboot, I usually don't
even see my DVD drive on the narrow SCSI bus till I power off and then
power on again. This is probably because only a poweroff/on cycle resets
the SCSI bus completely.

I am still trying out some new combinations, but I would appreciate any
tips from those of you who might have some special insight or
experienced similar situation and found the cure for it.

Rudy
 
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R

R. P.

Julian Knight said:
Don't forget that to achieve 480Mbps, USB has to make very heavy use of the PC's
CPU unlike SCSI and Firewire.
Firewire is as light on the CPU as SCSI? I had no idea. That's good
to know when trying to decide what kind of external HD backup drive to
get: USB-2 or Firewire.

Rudy
 
J

Julian Knight

From Jim Berwick on 02/Aug/2004 10:16:
[email protected]:




What PCI/PCI Express issues?
The fact that none of my PC's have PCI Express. If I upgrade to a motherboard
with it, I will have to replace: Memory, Processor and power supply at the very
least - again! If I don't replace, we are at the end of the line for PCI within
a few years.

If I choose USB it is likely to last another 10 years.
 
J

Julian Knight

From R. P. on 03/Aug/2004 07:15:
of the PC's



Firewire is as light on the CPU as SCSI? I had no idea. That's good
to know when trying to decide what kind of external HD backup drive to
get: USB-2 or Firewire.

Rudy
One of the reasons that Firewire has been more expensive than USB.
As someone pointed out though, perhaps some newer chipsets now don't need to hit
the CPU as hard? However, the spec does allow it.
 
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J

Julian Knight

From Glenn on 02/Aug/2004 14:47:
USB definately uses a lot of CPU power. When I have my USB scanner
driver GUI opened, CPU usage is 50% and CPU temps jump to about 50 C.

Julian, are you looking for a PCI SCSI card? I have one just sitting
here. I used it for optical drives, but I have gone IDE. I haven't
used it since August 2002, I assume it works, it's been boxed up since
then.
Thanks Glenn, but as I said in my other post, I think I would rather choose a
USB converter if I can simply for the flexibility (I can use it in any PC
including my laptop and lend it to friends without having to trash their PCs)
and the fact that I don't want to end up with another useless card when I next
upgrade my desktop.

I was interested though to here if anyone had used one of these converters,
especially with scanners.
 

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