Skip to content
Thoughtful, detailed coverage of everything Apple for 34 years
and the TidBITS Content Network for Apple professionals

SCSI Double Agents

If you use both Macs and IBM clones, you’ve probably wondered if you could buy a tape drive or CD-ROM drive or a removable cartridge drive or WORM drive or whatever that could be used both for your Macs and for your IBMs. I’m not talking about elaborate networking with servers and high-speed network communications. I’m talking sneaker-net, down and dirty: plug in the tape drive to your Mac and update one backup tape, then plug it into your IBM and update another backup tape. That’s a simple, economical approach for many of us and, if possible, would let us justify the purchase of nice new toys on the grounds that a single device could do double duty for a number of machines on both platforms.

Macs from the Plus up have SCSI ports, so when this possibility occurred to me two years ago I started looking at SCSI cards and devices for the IBM. I found some real problems. The old SCSI-1 standard (there is a faster, smarter, family-size SCSI-2 standard now) wasn’t much of a standard – there were a whole bunch of supposed "SCSI compatible devices" that weren’t compatible with much of anything other than the manufacturer’s own supplied SCSI adapter. But, you should be able to put up to six other devices on one SCSI card (the SCSI card itself takes one of the SCSI ID numbers from the usual seven, leaving six available for devices). If the cards and devices were not interchangeable, what could be done in a practical way?

Well, one approach was to buy the cards and devices from the same manufacturer. But that wasn’t easy. Dealers packaged everything for one platform or the other. If you wanted to use a NEC CD-ROM drive on a Mac, you bought the drive with a Mac interface. If you wanted it on an IBM clone, you bought the version with the IBM interface (including the card). If you wanted to buy the Mac version and then add the IBM card and software without the actual drive, good luck! No one sold it that way – nor would you want to fill your slots and empty your pocketbook buying different cards for each peripheral you added. But you had no assurance of anything working right if you mixed cards and devices from different manufacturers. What to do?

What I did was wait for some standards to be established, since it’s best to use a common language that all devices can understand. Now that enough time has passed we have some standards in this area. I know about three such languages: Microsoft’s Layered Device Driver Architecture (LADDR, which stretches the acronym), the Common Access Method (CAM), and the Advanced SCSI Programming Interface (ASPI). The arguments among these proponents are now settling, and my own bet is on ASPI, mostly because many vendors support it (it was created by Adaptec, which makes popular SCSI controllers) and because one software product on the market, CorelSCSI, is widely distributed and works only with ASPI drivers.

So here are my recommendations on how to buy Mac peripherals that will work with an IBM too. First, don’t buy anything old or used; stick to devices marketed since at least 1989. Second, check to see that your device is supported by the CorelSCSI drivers. Corel maintains a forum on CompuServe (GO COREL) and has a list of supported devices and controller cards available for downloading. You are concerned only with the internal mechanism. Many manufacturers sell Quantum hard drives, for example, packaged under hundreds of different names, but all recent Quantum drives are supported, regardless of the name on the external case.

Third, buy a SCSI Host Adapter card with ASPI drivers (usually priced between $125 and $200 for the latest SCSI-2 16-bit models); again, tested ones are on the Corel list. Many of these adapters will come with drivers for most of the devices you come across, and you will not need the drivers in CorelSCSI itself. In that case, you need not purchase CorelSCSI. But if you try to hook up a device and have problems, you might opt for CorelSCSI (which is sold with and without the controller card itself) for around $80 from the usual mail-order places.

Finally, buy the Mac version of the product so that you’ll be sure to get the software needed to run it on your Mac. I recently bought a Teac backup tape drive from Club Mac, although I could have gotten the basic external drive more cheaply from an IBM-only supplier. By buying from Club Mac, I received Retrospect as well, which would normally cost about $150 and without which I would have no way to back up from my Mac.

If all goes well, you should be able to just plug in your devices and use them. I’ve done that with a tape drive, CD-ROM drive, and an old SyQuest 44 MB cartridge drive. I’ve had two minor problems. The installation software for the card I use recognized the SyQuest drive easily but apparently regarded it as the newer 90 MB drive and reported that it couldn’t read the media after formatting. I had to format cartridges using SyQuest’s own software before the SCSI card could recognize them correctly (download DRIVER.ZIP from the SyQuest BBS at 510/656-0473). It turns out that CorelSCSI can install this drive through a custom installation in which you first identify the card as a Ricoh 50 removable and then make some changes in your CONFIG.SYS file. The details are in a file on the Corel section on CompuServe. The other problem? I couldn’t reinitialize a 1985 SuperMac DataFrame XP20 for DOS – the ROM in the DataFrame responded to a standard SCSI query about its capacity with a "0" and, recognizing that as an error and not knowing the true capacity of the device, CorelSCSI wouldn’t mount it. On the Mac, SCSI Probe had similar problems getting info from the device, by the way. (Hence my first rule above about sticking to new equipment.)

[Actually, it’s not in the least bit surprising that a DataFrame XP20 caused problems – those drives are notorious for causing problems even with third party formatting software when used on the Macintosh. -Adam]

— Information from:
Windows User — Feb-93, "Taming the SCSI Monster," pp. 158-162
Always Technology Upgrade Installation Guide for the
IN-2000 Adapter — 818/597-9595
CorelSCSI installation manual. Corel — 800/873-4374

Subscribe today so you don’t miss any TidBITS articles!

Every week you’ll get tech tips, in-depth reviews, and insightful news analysis for discerning Apple users. For over 33 years, we’ve published professional, member-supported tech journalism that makes you smarter.

Registration confirmation will be emailed to you.

This site is protected by reCAPTCHA. The Google Privacy Policy and Terms of Service apply.