View Full Version : AT&T Unix PC (7300/2B1) floppy reading

July 7th, 2014, 02:48 PM
Has anyone figured out a way to read 7300/3B1 UNIX PC floppies on other systems?

From looks of the 5.25" disks (8 and 10 sector), it appears to be a SysV filesystem, but with a different superblock and magic ID.

Any tips or confirmations? Were I to alter the superblock, would it be possible to BSD or Linux to read the disk?

July 9th, 2014, 07:33 PM
I got most of my 7300 software by downloading to disk and reading into 7300 using the UNIX. pc's DOS emulator card and/or Kermit-ing. When I return from my travels I can check details from manual, I remember going through hoops to accomplish. Exhibited my 7300 at HOPE convention in 2008.

July 9th, 2014, 08:10 PM
I've been offered a used 7300 but it has no keyboard and condition is unknown. It could well take me a long time to get it going.

I think I've got the details of the disk format down, so it's mostly of writing some code. Basically S51K with some twists as near as I can tell.

July 9th, 2014, 08:46 PM
there's something called DOS 73 that is used to read IBM DOS disks on a UNIX PC. I think there is a card you need to install that goes with it.

July 11th, 2014, 07:04 AM
The DOS73 card looks like this:

July 11th, 2014, 08:41 AM
I looked at the unixpc.org site and was a bit surprised not to find much on the floppy format. I did find a part of a ROM that someone disassembled that verified that floppies did use a modified SysV file system, with extra space allocated for a boot area--the boot code uses that instead of trying to work through inodes and such. Browsing the floppy, it's pretty easy to see the 2-byte (big endian) inode+14 byte filename directory entries. I'll probably tackle a reader this weekend.

July 12th, 2014, 01:37 AM
Hey guys, I just wanted to say that I am glad you are discussing this topic and others like it here.

I don't have any answers or ideas to share on this topic as of yet, but gaining this level of understanding of the way the UNIX PC operates is exactly why I am trying to get one working myself just this past week.

Just reading this discussion makes me want to figure out all of the answers to these questions myself.

Thanks for sharing this discussion here. It is inspiring and encouraging.


July 18th, 2014, 11:07 PM
Problem solved--rolled my own code to extract files from the diskettes and I'm fine now.

August 8th, 2014, 06:27 PM
Problem solved--rolled my own code to extract files from the diskettes and I'm fine now.

Hi, would you share the code? I've got some floppies still in a box I wouldn't mind recovering.

One glitch for me is that the got formatted 9 sector instead of the standard 8 -- this was a unix pc feature to get more space, if I recall.


August 8th, 2014, 07:40 PM
I think I responded in another thread that the Unix PC was basically a plain SysV filesystem with some Convergent "tweaks". On the unixpc.org, there are a set of "development' floppy images. Just concatenate them and run cpio on the result to get all of the important include (*.h) file definitions. Other than being big-endian architecture, it's not that different from a plain-Jane SysV implementation. I wouldn't dare inflict my coding on anyone...

Are you certain that you don't mean "10 sector" floppies and not 9? My own samples were 8 and 10 sectors.