Getting 360K (5.25" low density) disks to read and write reliably in 1.2MB (5.25" high density) drives:

Due to the recent surge of old software resources on the 'net, I've been downloading lots of Tandy (XT clone) software off web pages onto my Pentium, which has a 5.25" 1.2 MB drive, in the hopes of copying it to a 5.25" disk for transfer. Everybody knows that trying to write to a 360K disk in a 1.2MB drive usually works fine for the 1.2 MB drive, but then renders the disk mostly unusable for the 360K drive. (This is because the 1.2 MB drive is built for reading 80 tracks instead of 40, and the read/write head is narrower, which results in some residual "noise" left behind at the outer edges of each track that confuses the 360K drive's wider head.) This makes it frustrating to try to copy software over to the Tandy, since it's hit or miss whether or not you can actually read the data off the disk when you're done.

I've found a procedure to get around this that always works (at least, on my hardware): Bulk erase a low-density diskette, then low-level format it in the high-density drive. Detailed steps follow:

  1. "Bulk" (erase) a used or blank 360K disk with a tape bulk eraser (can be bought at Radio Shack or other places for around $12) or with the BULKERAS program that comes with CopyIIPC. This quickly and *completely* erases *all* information on the disk, including between-track data, GAP bytes, etc. (Don't bulk a disk you need the info off of--it is utterly unretrievable once bulked!) A bulk eraser is essentially a portable contained electromagnet, and quickly scrambles all data on the disk. The disk *must* be bulked--simply reformatting it won't work, since some residual noise is always left over, and it's the noise that screws up the 360K drive.

    (The disk must be a standard double-sided double-density diskette for best results, instead of a high-density disk. You can usually tell if it's double-density by looking for a spindle reinforcement ring--that little ring of a sticker on the middle "hole" of the disk. If it has a ring, it's most likely double-density; if it doesn't, it's most likely high-density. This sounds like folklore, but over 95% of high-density disks don't have a reinforcement ring--look at your own disks next time and you'll see what I mean.)

  2. Format the disk in the 1.2 MB drive with the following command-line (DOS 6.22 tested):

    format b: /4 /u

    The /4 tells dos 6.22 to format the disk in the 1.2 MB drive for 360K (40 tracks (double-stepping), 9 sectors per track, sector size 512 bytes, two sectors to a cluster). The /u is undocumented depending on your version of DOS; it means "unconditionally format the disk without checking it first".

    (Other versions of DOS's format and other format programs can probably do the exact same thing, and better; I have DOS 6.22, so that's what I'm reporting on.)

  3. Copy the software to the 1.2 MB drive. Try to write it only once; for example, don't copy a .zip file, change your mind, delete it, then copy a different one. Multiple writes to the drive tend to mess up the process.

The 360K drive should read the disk perfectly. You might get lucky and be able to write to the disk from either drive repeatedly in the future and still be able to read it in the 360K drive, but this varies from disk to disk and drive to drive. I usually repeat the whole process for each disk's worth of info I need to transfer over, since bulking and formatting it only take about 45 seconds.

The 1.2 MB drive used to test this was a 3.5"/5.25" dual unit teac; the 360K drive is the original installed drive in my Tandy 1000 HD.

Jim Leonard (Trixter / Hornet)                       Email:
-- My ears burn: -------------------------------------------------------------
<Khyron> trixter is a mad crazy phat crackhead