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June 2003

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SCSI on OS/2 - A Personal View

By Per Johansson© June 2003

This article is about my personal experience of using SCSI devices on my computer. I'm more of a software than a hardware person, but sometimes it's fun to try new hardware stuff. Although I'm an OS/2 user, most of my work is platform-agnostic, and most of my OS/2-specific knowledge is about making this and that hardware and software work. My profession is software developer.

SCSI Overview

I will keep this short, since SCSI is written about elsewhere, for instance at The SCSI Workshop (VOICE Newsletter March 2002) and Gary Field's SCSI Info Central.

SCSI means "Small Computer System Interface" and is a set of ISO / IEC standards for connecting devices to your computer via a standard hardware interface, which uses standard SCSI commands. Lately, SCSI has become less important for the average user since external devices such as scanners often use the USB interface and internal CD-writers, that formerly required a SCSI connection, now run happily on the IDE ( a.k.a. ATA) bus, which is what PC hard disks usually are connected to.

However, as an OS/2 user, there's no choice but SCSI if you want to use a scanner (Lately, Tame/2 has begun to provide USB scanner support).

SCSI advantages include up to 7 or 15 devices on a bus (as opposed to IDE's 2 devices), speed and quality of the device.

SCSI devices mean extra cost, but it can be kept down by getting devices from internet auction sites such as eBay. Doing this has worked fine for me so far.

Scanner and Adapter

My first entry into the world of SCSI was in late 2000, when I thought I was in need of a scanner. I chose the Umax Astra 2200 model, partly because it had both a SCSI and a USB interface. Also, it was relatively inexpensive, as the model was being phased out. Unfortunately, USB seemed to be the default connection, so there was a USB but no SCSI cable included.

You also need to get a SCSI adapter (an expansion card), unless your motherboard has SCSI built in, which is rare. Here in Sweden, the retailers mainly stock adapters from Adaptec (expensive) and Tekram (sometimes less expensive). Now, connectors on SCSI adapters are either 50-pin or 68-pin (a.k.a. Wide). Modern hard disks use 68-pin, while devices like DVD players and CD writers use 50-pin. Scanners usually have 25-pin connectors ("The Apple kludge"). There are also 80-pin (SCA) connectors, for high-end devices, of little interest for a home user.

I won't go into details about the different connectors and SCSI versions. See above links, Storage Review and Adaptec for more info.

I went for the cheapest adapter I could find, the Tekram DC-395U with an external and an internal 50-pin connector. Since I thought I'd be using it with the scanner only, I looked for an adapter with a 25-pin connector, but such animals were not to be found. I also bought a cable with 50 pins on one end and 25 pins on the other (there's also the possibility to use a 50-25 converter). Finally, I bought a passive terminator. SCSI buses need to be terminated in both ends either by a device or by a terminator. The adapter would terminate one end, but the scanner provided no termination, hence the need to get the terminator.

Another thing to do with the SCSI adapter is known as "flash the BIOS", meaning that you download the latest BIOS from the manufacturer and install it on the adapter. The reason for this is to have more features and less bugs. This is usually done while booted from DOS and using a special flash program. This can also make the adapter unusable if something goes wrong, such as a power blackout during the flashing. But we need some adventures and excitement in our lives, don't we? So I flashed the BIOS to the latest version on all adapters.

Installing the Tekram DC-395U SCSI adapter just means putting the OS/2 driver in the \os2\boot directory and adding the line basedev=trm3x5.add to config.sys. Same with other adapters, just add the pertinent driver for your make/model SCSI adapter.

This scanner worked fine when I had installed the software, which I bought from CFM, since the included software didn't... well, you know. CFM's OS/2 development seems to have come to an end so better look elsewhere for drivers now.

Hard Disk and Another Adapter

One year later, I thought I needed a bigger hard disk, and it would be a good idea to buy a SCSI one. These are two or three times as expensive as IDE hard disks, but who cares? I bought a less expensive one, IBM Ultrastar 36LP. It was now I discovered that current hard disks all had 68-pin connectors, so another SCSI adapter was needed. I had no objections to Tekram, so I bought the DC-395UW, which is similar to the other one, except that there's also an internal 68-pin connector. Again, this disk had no termination, so I bought an active terminator. Active ones are better than passive ones, and I thought it would be the better choice with a hard disk on the bus. The power line on the bus cable may be too weak (that is what the passive terminators use), especially for longer cables.

Now a problem: this SCSI adapter could see only 8 Gbyte of the hard disk! Flashing its BIOS didn't help, and no newer OS/2 driver was available. This is a known problem and there's nothing to do about it. I guess I should have returned this useless adapter to the retailer, but I kept it anyway for some reason.

Third Adapter

I looked through the newsgroup discussions about good and inexpensive SCSI adapters, and now opted for the Tekram DC390F. It had a Symbios SYM53C875 chip, not a Tekram chip like the others. It would use the tmscsiw.add driver. Unfortunately, this driver consistently failed to load. However, there's a fallback driver, the sym8xx.add from Symbios, now LSI Logic. This one loaded fine, but a new problem struck: I could not boot from the hard disk! I spent some days rearranging the hardware and the load order in config.sys, but the boot always halted at "something".dmd. I asked at Usenet, and learned more than I thought I'd ever need about the OS/2 boot process, but to no avail. No help from Tekram either, and the support at LSI Logic just replied that their driver wouldn't support the Tekram adapter, and I would have to use the Tekram driver. To this day, I haven't resolved this problem.

I kept a boot volume on the old IDE disk, and moved the other volumes to the SCSI disk. I always separate the volumes like that anyway.

The DC390F's external connector is a 68-pin as opposed to the other adapters' 50-pin. This meant that I had to buy another SCSI cable to get rid of the old DC-395UW adapter.

DVD Player

Next, I figured I had to get a DVD player. The only relatively inexpensive SCSI one I could find was the Pioneer DVD-305S. It has a 50-pin connector so it can't be connected to the same cable as the hard disk (it can with a converter, but it's probably better avoided). Furthermore, on a single channel adapter, one can't connect to all three connectors of the adapter at the same time, due to the SCSI topology. Since the scanner, the hard disk and the DVD player were on three different cables, this meant that I had to bring the old DC-395UW adapter back into action. It soon turned out that connecting the DVD player to that adapter wasn't a good idea. The system would trap at any time when the player swung into action. The safe configuration seemed to be having the hard disk and the DVD player on the DC390F adapter and the scanner on the DC-395UW adapter. Fortunately, the player had termination built-in, so another terminator wasn't necessary.

CD Writer

The next move was to bring a CD-writer into the mix. I use it mainly for backups onto CD-RW and transporting data (and eComStation betas!). By now, I had finally learned how to use internet auction sites, and I guessed I could get a cheap device there. It happened to be a Lite-On brand, which turned out to be another mistake as it wouldn't work with the RSJ CD Writer software! RSJ support told me that they were aware of the problem, but had no solution for now. So I got rid of this device and got myself an HP CD-Writer+ 9200 1.0c. It works, but can only be flash upgraded using Windows 9x! (Many hardware devices can be flashed, not just SCSI adapters)

One SCSI-unrelated fact I wasn't aware of at the time is that these old CD-writers write to CD-RW at 4x speed only, while newer ones write at 12x. They use different discs too. This means that my backups take longer time than necessary. On the other hand, next step is probably to get a DVD-writer anyway.

Fourth Adapter, and Good Bye IDE

Finally, I felt the need to get rid of the IDE hard disk that was needed for booting OS/2 (but not DOS or Windows). I had enough of Tekram's offerings (although other people are happy with their products, except the 395 series that no one seems willing to defend) and I wanted an Adaptec adapter. I decided to go for the newer Ultra160 ones, the 29160 or 29160N.

I was inspired by the article Adventures in Adaptec U160+ Land in the December 2000 VOICE newsletter. I found a 29160N at the QXL Sweden auction site. I was a bit nervous since I had read warnings that OEM adapters may not work and may not be able to be flashed. Anyway, I got the adapter, and it looked like a standard adapter. I flashed it with the latest BIOS, and installed it with the aicu160.add driver.

Unlike the Tekram adapters, it warned me that the cable with the CD-writer and DVD-player was badly terminated, and yes, both devices had their termination turned on which shouldn't be the case! After verifying that the adapter worked, I backed up the contents of the SCSI hard disk, moved the cable from the Tekram to the Adaptec adapter, and did a low-level format. This is recommended when you change to another adapter, but I don't know if it was necessary. Then, I restored the backups, and moved the boot volume from the IDE hard disk using DFSee. And now, I could boot from the SCSI hard disk! Soon thereafter, the IDE hard disk was removed along with the IDE drivers.

There's one more thing to do: the Adaptec adapter and the hard disk can operate in LVD mode, but they will need a special cable and terminator for that.


The SCSI devices show up like this. The first four images are real screenshots from a digital camera, so I apologise for the quality.


The SCSI Workshop:
Gary Field's SCSI Info Central:
Storage Review:
Adaptec SCSI Connectors:
IBM (now Hitachi) Ultrastar 36LP:
Tekram DC-395U:
Tekram DC-395UW:
Tekram DC390F:
LSI Logic:
Pioneer DVD-305S:,1444,1744,00.html
HP CD-Writer+ 9200 1.0c:
Adventures in Adaptec U160+ Land:
Adaptec 29160N:

Per Johansson is a systems developer in his native Sweden. He can be found on IRC in Undernet #OS/2 and other channels as Hawklord. You can visit his home page at where you can read more about his interests in travel, media and of course computers.

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