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Conversion of 1.44Mb to 720Kb floppy disk doesn't work as expected

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djyuran

Experienced Member
Joined
Dec 27, 2017
Messages
53
Location
Seattle, USA
Hello!

I got 8088 laptop Panasonic Business Partner 150 (https://space-nerd.com/en/1990/05/2...150b-no-frills-laptop-features-bright-screen/).
Person I bought it from replaced FDD to 1.44Mb but controller supports only 720Kb 3.5".
I have a lot of 1.44Mb floppy disks so I converted several disks to 720Kb with a patch on a small window and formatted them to 720Kb.
They work well on my other retro PCs (with 1.44Mb FDD) but they work weird with this laptop.

FAT is readable but when I try to copy a file it shows me a error with Abort, Retry, Fail.
Retry sometimes helps. So it works but very unstable and mostly unusable for me.

What could be a reason?

I found an interesting explanation here https://www.instructables.com/Convert-a-144mb-floppy-to-720k/
"I have experienced that converting an HD (1.44MB) to a DD (720K PC/800K Mac) disk this way it may cause problems when the disk is used and already formatted in the HD format.
The original HD layout will not be properly erased, instead only the DD format will be recorded over the HD format causing an unusable disk."
Does it sound correct?
 
djyuran said:
Retry sometimes helps. So it works but very unstable and mostly unusable for me.
Click to expand...
That's exactly what is supposed to happen. You can not just turn a HD disk into a DD one, as the material used is different. A HD disk needs a higher magnetic field to store data in a reliable way. A DD drive or a HD drive in DD mode uses a signal which is too weak.

Solution: get some real DD disks.
 
Replacing DD drive with HD drive should not be in any way problematic. HD drives are capable od DD operation. They should switch to DD mode automatically when a DD diskette is inserted.

Why dont you try DD diskettes?
 
Bulk erasing the HD disk can help. The magnetic coercivity of 3.5” DD and HD media isn’t very different (compared to the differences in 5.25” media) so most DD drives do “okay” with reused media, but I found, for instance, that the internal drive in my 512k Macintosh had issues overpowering the format already on a newly recruited disk. My black magic solution was to wave a powerful refrigerator magnet over the disk for a minute or so (weaving around in a circular pattern over the entire donut), and it usually works.

I do have my doubts that disks written in these drives that seem to have unusually weak head strength will be reliable over the long haul, but they seem fine for scrap use. (IE, maybe use them for your program disks, save data you care about on actual DD disks.)
 
It isn't the magnetic characteristics of the coatings between 3.5" DD and HD disks that's the critical thing, but rather the coating thickness and particle size. You can usually see through the coating in an HD disk in strong light, but usually not so much with DD.

I do routinely bulk erase disks before formatting (I detailed how to make a very effective bulk eraser using a couple of ceramic ring magnets salvaged from an old microwave oven magnetron. Electronic junk does have its uses.) mostly because some old disks contain customer information and I want to be able to say that nothing escaped.

That being said, I reported last year on an interesting situation where I have a system that records GCR at somewhere around 400Khz on 5.25" DD disks. Works fine, but I wanted to archive some of the data from 1978-1980 on 3.5" floppies. I rigged up an external 3.5" HD drive off the controller and figured that if 5.25" DD floppies worked, then 3.5" DD floppies would also work.

Errrrp! No--my success rate with brand new 720K floppies was only about 1 in 6 decent copies. So, I figured that I'd try HD floppies (the drive is media-sense). Errrp! No such luck. So, as a last attempt, I taped over the media sense hole in a few old 3.5" HD disks. Result--perfect every time, even with old floppies that wouldn't format perfectly as HD ones. My guess is that "ideal" media characteristics in this case falls somewhere between DD and HD. (A year later and disks still read just fine).

Life can be very strange and often throws us unexpected curve balls...
 
I will say that I don't have a single surviving DD floppy formatted to HD. Used to get a few of them back in the PS2 heyday; I found it very annoying on my media-sense drives. Given the price differential at the time, some folks either drilled holes or punched them in DD floppies to make them work as HD in media-sense drives.

They just didn't last.
 
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