MicroVAX I Floppy Drive

Having archived the disks i tried to mount them on the Microvax.

Each disk has a “label” written to it. I didn’t know the labels for these disks but if you put in a random word it will fail and tell you the actual label. I found most would not mount regardless.

$ mount dua1: <label>

I also tried to initialize a fresh disk but this also failed which didn’t seem like a good sign. I even tried a disk that had been erased with the Greaseweazle erase function. No joy.

$ initialize dua1: test

It was the same with the second drive. This dual drive is a curiosity in that it has only one hub motor and one head position motor shared by the two drives. The disk is inserted upside down in the bottom drive.

At this point i thought it would be worth pulling the drive, giving it a good clean, and testing it out with ImageDsk on an old PC. I found enough commentary on the web to believe that the interface was generally consistent with the shugart interface – noting that there are a few variations.

This allows the alignment to be checked and some read/write tests to be done. Alignment relies on reference disks and with the drive being 80 track double density my commercial DOS disks weren’t going to cut it. Instead, i just used the disks that came with the machine.

One of the pressure pads was loose and the other seemed to be worn. I re-glued the good one and replaced the other with a handcrafted felt.

The rotational speed was good, but the drive was a little out of alignment. Adjustment is by loosening the head position motor screws and rotating the body a little. DEC have made this more awkward than it needed to be:

1. Remove the rear side plate screws and loosen the middle ones.
2. Remove the rear PCB
3. Loosen the screws on the body motor – but just a little
4. Reassemble
5. Test and adjust (it is hard to get a good grip) using the Image disk alignment function
6. Repeat steps 1-2. Tighten the motor body screws.
7. Reassemble

After this i could mount all the DDSS disks that came with the unit. They generally have backup files on them so i have not had time yet to install.

I still found there was a problem initialising disks. I could only initialise disks that had been previously initialised. I think this may be a DEC thing. I suspect that they sold pre-formatted disks rather than providing a genuine format program.

It is easy enough to work around this by writing an archived disk using greaseweazle and then initialising it. Once that’s done the freshly initialised disk can be archived and used to write more formatted disks.

Lexitron pulled a similar swifty with their word processors.