MicroVAX I Archiving Floppy Disks

The system came with about 15 floppy disks which were archived using a Greaseweazle. Several were a high density format, one was not a VMS disk, and the rest were RX50 format. The first thing i wanted to do was to archive these disks.

There is some basic information on the rx50 format here:

https://www.vaxarchive.org/hardware/rx50.html

I wasn’t sure if the disks were RX50 disks so i started by reading them as SCP files using greaseweazle.

An 80 track 96 TPI drive capable of writing double density disks is required. One option is the rx50 itself, but there are other drives that work fine as well. I have previously used a Panasonic JU-475-5 drive for making 80 track disks for the Sirius One and the BBC Master. I’d expect other drives to work as long as they observe the density select pin including changing the rotational speed to 300rpm for double density disks.

These disks can be archived with greaseweazle simply by reading the flux into an SCP file.

gw read --revs=5 --tracks="c=0-79:h=0" <file>.scp

I could then load them into the HxC software for a look.

Then i exported them to IMG.

Greaseweazle is also capable of doing the conversion using a custom disk format and this is the more efficient approach if you already know the disk format.

# Example custom.cfg
disk RX50
  cyls       = 80
  heads      = 1
  tracks * ibm.mfm
    secs       = 10
    bps        = 512
    interleave = 1 
    rate       = 250
    rpm        = 300
  end
end

gw write --diskdefs=custom.cfg --format=rx50 <file>.img

Greaseweazle could attempt the deinterleave here by setting interleave=2, but it turns out to be more convenient to not do this.

There was nothing particularly notable about the media. Given the format is 80 track 96 TPI single-sided disks i expect DEC would have insisted on quad density disks, but generally this was a labelling/certification exercise rather than any fundamental difference from normal double density (or single density) media. The disks that were labelled were single sided double density.

As it turned out, some of the disks were high density disks (probably RX33 compatible) and one was not for the MicroVAX at all.

I was hopeful of retrieving some games from them but it turns out that the first disk in the backup set is rotten. The remainder of the disks don’t have a lot of interest. Sometimes the journey is more interesting than the destination.