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Disk overlays, FreeDOS, disk-archiving and Photography

2023-03-09

Last few weeks I've spent more and more time down in my basement

darkroom. I've worked with some printing projects, but mostly I've

been spending time with the old 486 and the OpenBSD workstation I keep

down there. The greaseweazle I got some months ago has been frequently

used to dump old discs. I have started getting some of the floppies I

ordered through the auction-site, and I've started doing disk-dumps in

a more controlled manner. I also got a good deal on some random 5,25"

disks in a local thrift-shop that I munched through quickly. Mostly

PC-stuff, really ancient DOS-boot-disks and the like. Also some local

word processors and spreadsheet software that I think will make a

good addition to archive.org. I also got a large box of Amiga disks

that proved to contain some cover disks from computer magazines. These

have so far proven to be mostly overwritten and re-used unfortunately,

so not very interesting to upload anywhere I guess.

I also got my CF-card reader working on the 486, by using an old

disk overlay. There were several choices, but I ended up using

Ontrack Dynamic Disk Overlay. It worked like a charm, and I was

able to format the 16GB CF-card to FAT32 and install FreeDOS 1.3

on it successfully. The problem with disk overlays is of course

that they tend to confuse systems that will not run the code they

place in MBR, so if you try to insert the card in, for example,

an OpenBSD-machine with an USB-adapter, it will not find the FAT32

partition, only an unknown entry in the partition table. I was able

to find a solution to this, in an old twitter thread of all places!

The user "Foone"/"@Foone" made a thread in 2021, where it is described

that you can use losetup to mount a Ontrack-formatted disk with an

offset, to skip the first part of the disk where the overlay resides,

and make it mountable. It works well after testing, the only problem

I see is that OpenBSD does not have losetup. It instead has vnconfig,

which lacks the possibility to set an offset of the image you are

adding. I'll look further into it, but worst case, I can use Linux

on another system I have in the basement to access the card. Not

that convenient, but at least a lot better than transferring files

through floppy images via the Gotek I have installed. I'll link Phils

Computer Lab (where I found the Ontrack software and disk image)

and the Twitter thread below. I don't use twitter, so I cannot thank

Foone for this great thread though.

This is how I used a disk-image of the CF-card I made to test it out:

sudo losetup -o $(( 16#fc00 )) /dev/loop5 CFCARD_FREEDOS_ONTRACK.img
sudo mount /dev/loop5 /media/removeable/image1 -o uid=1000,gid=1000

The number "fc00" will probably differ for you. I got to that by

checking with hexdump -C to find where "FRDOS5.1" was occuring.

The example from Foone was using MS-DOS, so in that case, it would

have been "MSDOS5.0" or something instead. This is what my output

looked like:

---SNIP---
0000fbf0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 55 aa  |..............U.|
0000fc00  eb 58 90 46 52 44 4f 53  35 2e 31 00 02 10 20 00  |.X.FRDOS5.1... .|
0000fc10  02 00 00 00 00 f8 00 00  3f 00 ff 00 3f 00 00 00  |........?...?...|
0000fc20  db 06 dd 01 92 3b 00 00  00 00 00 00 02 00 00 00  |.....;..........|
0000fc30  01 00 06 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
0000fc40  80 00 29 11 5f ba 07 44  49 53 4b 31 5f 56 4f 4c  |..)._..DISK1_VOL|
0000fc50  31 20 46 41 54 33 32 20  20 20 fc fa 29 c0 8e d8  |1 FAT32   ..)...|
0000fc60  bd 00 7c b8 e0 1f 8e c0  89 ee 89 ef b9 00 01 f3  |..|.............|
0000fc70  a5 ea 7a 7c e0 1f 00 00  60 00 8e d8 8e d0 8d 66  |..z|....`......f|
---SNIP---

I've actually also spent some time updating my photo-projects on

158.nu. A new album / project was introduced, that I called "The

perception of doors". It's basically a cliché door-photo-project,

but I kind of like the idea of it. Even if it is pretty cheesy

and over-done these days. Most of this first update contains old

photos from several years ago, but I've also thrown in stuff from my

vacation last summer. The name is of course a nod to Alouds Huxley's

"The doors of perception".

I also have other projects in mind that I will

probably develop during spring/summer. I need to get back to actually

photographing more. My motivation is always low during winter, since

it is pretty cold and snowy up here, but once spring is coming along

it's a lot more fun being outside.

Ontrack Disk Manager, on Phils Computerlab.

Twitter-thread by Foone, with instructions for mounting Ontrack-disks on Linux.

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