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5.25in DD disks, reading in DD drive after writing in HD drive?

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First post, by torindkflt

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I have two vintage PCs with 5.25in floppy drives. One of them has two double-density drives, and the other has one high-density drive. The system with a high-density drive also has a 3.5in floppy drive, so I would like to use it as an intermediary to copy files onto the system with the double-density drives. Now, I know that double-density disks written in a high-density drive are borderline impossible to properly read with a double-density drive simply because of the mechanical differences between how they are physically designed, and of course this is causing me some extreme difficulty.

What I would like to know is if there is anything I can do, other than replacing or swapping drives between the two systems, that'll make it easier for double-density disks written in a high-density drive to be read in a double-density drive. Perhaps a special utility to "half-step" the write head on the high-density drive to write the same data twice to the wider double-density tracks, if such a thing exists? Or maybe a Debug command I can run on the double-density system to do an equivalent of a low-level format on the disks between copies to help reduce noise and cross-contamination of the different track widths? FORMAT /U doesn't help at all. If at all possible, I'm interested in software-only solutions, as I'd like to avoid tearing these machines apart yet again just to copy some files.

Please be aware that the system with the double-density drives is currently only running a bare basic minimal install of DOS 3.3 and therefore has no terminal programs or any other means of copying files via serial. I'm limited to what's currently on the hard drive, and whatever I can get onto disk using the other system that it is then able to successfully copy.

Thanks for any assistance on this potentially futile endeavor.

Reply 1 of 4, by Malvineous

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Can you get hold of a degaussing wand for demagnetising CRTs? I've heard if you use those they can reset the disk to a "neutral" state, which in theory will at least remove the crosstalk from the other half of the track.

The only method I'm aware of to write the same track twice is by using a Kryoflux, but even they recommend using a DD drive to write DD disks.

Sounds like the first program to put onto the floppy is a program capable of receiving files over a serial port!

Have you tried sending a file over the serial port just by using DOS commands? e.g.

copy test.exe com1   ; Run on source PC
copy com1 test.exe   ; Run on target PC

You'll probably have to press Ctrl+C to end the copy, and might need to look up the MODE command to work out how to set serial port settings, but it might at least let you get enough files across to run a proper terminal program to copy other things.

Reply 2 of 4, by torindkflt

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I don't have access to a degaussing wand...would a strong neodymium magnet work? 🤣

Update: Actually, it DID work! I ran a neodymium magnet over the disk radially outward from the center, making sure to slowly work around the disk. Then I formatted it in the high-density drive, copied some files onto it, and put the disk in the double-density drive. It read the disk no problems. 😀

I did not know it was possible to copy files via serial directly from the command prompt! I shall have to try that as soon as I can locate a 9pin/25pin serial adapter. 😊

Reply 3 of 4, by Malvineous

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Interesting! I think the key is a continually changing field, so if you move the magnet too slowly it may be less effective, or you might have to do it a few times to get the effect you need.

If you do copy files via serial port, make sure you have used MODE or similar to set both serial ports to the correct baud rate etc. I'm not 100% sure whether MODE from DOS 3.3 could do this, so it probably hinges on that.

Reply 4 of 4, by torindkflt

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Indeed, I did move the magnet fairly quickly, but slowly rotated the disk in increments so there was some overlap to make sure the entire disk was evenly erased. I did learn that I have to repeat this process every time I want to change files on the disk, so it is kinda tedious for copying a lot of files. But, at least it's a means of getting INTERLNK or another terminal program onto the system...assuming they'll run on it since it's actually not quite 100% IBM compatible. 🤣

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