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foone @Foone
, 16 tweets, 4 min read Read on Twitter
Time to see if my disk imager can handle DMF disks!
DMF is a weird subformat Microsoft designed to squeeze 1680 kb onto a 1.44mb HD disk.
You might think such a small increase is pointless, but keep in mind: This program ships on 33 floppies.
Sticking an 240k per disks means they don't need /38/ floppies.
That's 5 floppies saved for each copy sold.
"an extra", I mean.
BTW the answer appears to be "NOPE!"
huh. trying just a simple dir on the first 4 floppies gives me 4 different errors.
weird. maybe this drive is fuckt?
yup, this drive can no longer read a standard 1.44mb disk.

I'd have to search far and wide for a working 3.5" disk in this day and age!
oh here's one. I didn't even have to get out of my chair
uh oh.
swapped the drives, and it still isn't working.
that's not a good sign.
OK so I switched to my desktop, which has a USB-based 1.44mb drive, and it can explicitly only see 2880 (512byte) sectors.
So while it can view the FAT and looks like it can copy the disk just fine... it'll error out if you try, because the disk has more sectors than that.
so this is not something I can fix in my reader.
the best I could do is put in a "uh-oh, this appears to be a DMF disk and your drive is limited to 1.44! Go image it on a better drive, please" message
This is what happens when you copy it on a USB 1.44mb drive.
OK now it has a "sectors per track" option you can pass, which'll let it read a 1680k DMF disk just fine.
Next step: autodetect when it's needed, from the BPB
Fun fact: Windows has an IOCTL to get the geometry of a disk, which should tell you if it's a DMF disk or not.
Less fun fact: IT FUCKING LIES TO YOU.
If you're using one of the USB drives that can't do more than 1.44mb, it'll just lie and pretend the disk is 1.44mb
For comparison, the same disk in a non-USB drive
I guess it does give me a way to detect if you have a 21-sectors-per-track supporting drive or not.
Just manually parse the BPB and see if windows is lying to your face about what the BPB says.
BTW, the MediaType 2 means "1.44mb 3.5" disk".
There's no MediaType for a 1.68mb 3.5" disk, because you can't expect Miccrosoft to properly support weird floppy disk formats created by small companies like *lemme check who made DMF* oh yes, Microsoft.
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