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[OM] [OT] SCSI Question, was: OT computer question but related to OM

Subject: [OM] [OT] SCSI Question, was: OT computer question but related to OM
From: Chuck Norcutt <chucknorcutt@xxxxxxxxx>
Date: Sun, 20 Apr 2003 08:11:20 -0400
Mike gave his tale of woe regarding his "SCSI" cards, cables and devices. The two Toms said:
---------------------------
<snip> I do not understand why it is you say you cannot connect the two
> scanners to the same (existing) SCSI-card. Except, of course, if your
> scsi-cards are seriously crippled....
-----------
They are, at least the one that came with the E3 is.  The card will NOT
support more than one SCSI device. Can't for the life of me explain why, but I used to have one. Probably still have the card, but the scanner is long gone.
---------------------------
Warning:  Long tutorial coming up.
The two Toms have almost smoked this out here. The first advice is that a user of an older PC device should not ask SCSI advice from a Mac user. SCSI is very complex being a somewhat abbreviated form of the original IBM 360 mainframe's data channel architecture which could support 16 devices. Being complex, it was very expensive to implement fully in PC hardware of some years ago. Macs have employed SCSI for a long time and have always fully implemented the SCSI standard of the day (of which there are about a half dozen)... cost be damned.

PC manufacturers discovered that SCSI was good for high data rate peripherals (like scanners) but too expensive for a competitive market. Their solutions in the earlier days (but not recently since the hardware had gotten lots cheaper) was to build custom "SCSI" cards tied directly to their (single) peripheral. These adapters are "SCSI" in name only. They do not fully implement the SCSI standard and are only meant to support the single, specific device they were designed for.

In addition to bus mastering, a true SCSI device must support daisy-chaining from one device to the next. The first thing to look for is a second connector on the device for attaching to the next device in the chain. I'm not familiar with the specific Microtek and HP scanners mentioned here but if they don't have the second connector it's an immediate tip-off that the supporting "SCSI" cards are probably custom designed for each specific device.

Here is an alternative solution since Mike seems to have at least one available PCI slot. I'm not familiar with the Microtek Scanmaker E3 flatbed but given the ISA "SCSI" card it is fairly old. My supposition (and it's only a supposition) is that even low end flatbed scanners of today will equal or exceed the performance of the (once probably expensive) Microtek.

If you have access to a Staples or other large office supply chain store watch their adds for scanners. Staples frequently has deals on Visioneer USB flatbeds that, after rebate, typically cost no more than $20. These are not top-of-the-line, state-of-the-art but still do a pretty decent job and probably as good or better than the older Microtek. I've had two Visioneer flatbeds and have only paid $20 for each of them. I bought the second one (Visioneer OneTouch 5800) since it was technologically better than the first and gave the first one to my daughter. Unless you're trying to use a 35mm transparency adapter, 300-600 dpi is as much as you'll ever need from a flatbed. What you might give up over a much more expensive scanner is a bit on the dynamic range.

To the $20 for the scanner add another $10-20 for a USB 2.0 adapter and Win98 compatible driver. The inexpensive scanner will probably be USB 1.0 but can still be plugged into the USB 2.0 interface. Pretty soon even the cheap scanners will probably be USB 2.0 but USB 1.0 is plenty fast enough since the data rate is throttled by the mechanical speed of the scanner.

This gets you a scanner that is probably as good as what you've got and gets rid of one of the pseudo-SCSI cards. It gets rid of an IRQ-eating ISA card and substitutes a PCI card which can share interrupts. With judicious shopping you can probably do this for not more than the cost of the SCSI cables you would need even if your problem can be solved via cabling (which it probably can't be).

Chuck Norcutt
Woburn, Massachusetts, USA



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