SCSI Magic

Device Types
Removable-media devices can fall under any of several SCSI device categories: direct-access read/write devices, sequential-access devices (tape), direct-access read-only devices (CD-ROM), and write once/read many (worm) devices are all commonly used schemes. Of these, the direct-access read/write devices are of the most interest to us, since these devices use the same command set as standard SCSI hard drives. This means that these devices can be added directly to a CMD HD system without any real need to adapt the HD-DOS.

When it comes to direct-access removables, there's yet a further breakdown; different technologies and mediums are employed by the various manufacturers to provide us with a wide variety of storage capacities. There are floppy drives, flopticals, rigid-disk cartridges and more. While I haven't had the opportunity to try all of these, most should be similar in many respects so far as how they operate under SCSI.

CMD Controller Requirements
While most of the direct-access removable devices can probably be used with a CMD HD system, the one device type that we can be sure will work well is the Syquest, a removable rigid-disk cartridge drive. Why the Syquest? That takes a little explaining...

The CMD HD system was designed primarily for use with hard drive mechanisms -- devices which have a fixed size, and which are willing to report that size to you when asked properly. One of the things that the CMD "ADD DRIVE" utility does when adding a new device to the system is to poll the device to see how big it is. This is necessary in order to maintain internal tables used by HD-DOS for creating and locating partitions quickly.

The Syquest drives respond to this polling in the same manner as a real hard drive would, so no special new utilities are required to add a Syquest drive to a CMD HD system.

Which Syquest?
Syquest makes a variety of drives in different sizes. For many years, these drives came in only 44 MB and 88 MB sizes, both in 5.25" cartridges. Early 88 MB Syquest drives couldn't read the 44 MB cartridges, but later models accepted both. Eventually, Syquest added a 200 MB cartridge and drive to top off their 5.25" line. This latter model can read and write all three of the 5.25" cartridge types.

Ever striving to improve, however, Syquest has also created two 3.5" drive models. The first of these to arrive was a 105 MB model; this was quickly followed by a 270 MB unit which is currently the highest capacity model Syquest manufactures. These drives are faster than the older and larger types, but any of these drives will offer equal or better performance than the old Seagate hard drive mechanisms originally used in the CMD HD drives.

Reliability
In the past, many have questioned the reliability of Syquest cartridges. In my own experience, I've found them to be very reliable on their own. I should note, however, that removing a Syquest cartridge at the wrong time can and will cause data loss. Used properly, though, the cartridges appear to be as reliable as most hard drives.

Adding a Syquest
There are some very simple steps to follow when adding a Syquest drive to an existing CMD HD system. But first, make sure you get everything you need when you buy the unit. It should be an external drive with its own case and power supply; ask the vendor you buy from to include a terminator and a SCSI cable (DB-25 to Centronics 50-pin SCSI).

Before you attach the Syquest drive, use the HD-TOOLS program to allocate as much of your current HD as possible. When you finish this step, you should have less than 256 blocks available for partitioning.

Now hook up the drive to the HD using the SCSI cable, and place the terminator in the second SCSI port on the Syquest. Set the SCSI device number to anything but 0 or 7. Turn on your equipment, and place a cartridge in the Syquest. Now run LLFORMAT to format the cartridge (this will take a few minutes). Once the cartridge has been formatted, run ADD DRIVE to add the Syquest to your system.

At this point, you're all set to add some new partitions. This is a little tricky. First, create a 256-block FOREIGN partition, to act as a "bridge" between your hard drive mechanism and the Syquest. Now you can create whatever partitions you wish, but keep this important fact in mind: Every cartridge you use will have the same partition arrangement, since the partition table is kept on the main hard drive -- not on the cartridge.

Whenever you get a new cartridge, you'll need to use LLFORMAT to low-level format it. Don't run ADD DRIVE again, though, since the drive has already been added. Don't try adding new partitions, either, unless you didn't use the full capacity when you created partitions for the initial cartridge. DO format each of the individual partitions you created for the previous cartridge, using the standard HD-DOS format command. Since you're using a new cartridge, these will appear to be unformatted until you do.