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Thread: HD on 3.5" DD floppies--DON'T DO IT!

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    Default HD on 3.5" DD floppies--DON'T DO IT!

    Got a bunch of 1.44M-recorded 3.5" floppies the other day for data recovery.

    About half were written on DS2D (720K) floppies. IBM PS/2s could do this, as they aped the 1.2M drive and used host-determined (not drive/media-determined) density. The batch I have here were written about 1988.

    The 720K disks worked for some time and saved a pile of money (my first box of 10 HD 3.5" floppies cost somewhere north of $40, while a box of DD floppies could be had for $10). For those non-PS/2-ers who wanted to do the same, you could purchase a punch that would produce the high-density aperture in a DD floppy.

    The proponents pointed out that the coercivity of the coating between the two was pretty close. That was about as apt as pointing out that beef gravy worked as well as chocolate in an ice-cream sundae because both are brown. There's more than one measurement that separates the two type of media.

    So today, I have to inform a customer that, while the data on his echt HD media, by and large is still good after almost 30 years, the stuff on the DD is only about 30% recoverable. Literally, the data on the tracks past about 20 isn't recoverable.

    For that matter, I can remember resorting to the "add the hole" method for creating HD floppies back in the day. Not one has survived intact.

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    These days DD floppies are so rare I've resorted to doing the reverse, bulk-erasing HD floppies so I can use them in double-density machines. (Specifically old Apple 3.5" drives.) I've gotten away with it (in the sense the disks will usually work semi-reliably in most of the drives I've tried them in, at least for a while), but the only thing I ever use those disks for is writing OS and program disks that are disposable and trivial to recreate.

    Back in the day, though, the fact that PS/2s would let you do this without even trying was a huge pain in the neck. It happened *all the time*, someone who wasn't even trying to cheat the system would format a DD disk to 1.44MB because that was the default on their PS/2 at work and bring home work on it which they subsequently couldn't read on their generic PC. I kind of suspect this was a significant factor in preformatted floppy disks becoming a thing.
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    You could punch a density hole in the 720K disks written as 1.44M and read them on a standard drive--for awhile anyway.

    But crikey--you'd think that since the standard for the HD media mandated an indicator hole, IBM would have enforced checking for it. Nope.

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    Quote Originally Posted by Eudimorphodon View Post
    These days DD floppies are so rare I've resorted to doing the reverse, bulk-erasing HD floppies so I can use them in double-density machines. (Specifically old Apple 3.5" drives.) I've gotten away with it (in the sense the disks will usually work semi-reliably in most of the drives I've tried them in, at least for a while), but the only thing I ever use those disks for is writing OS and program disks that are disposable and trivial to recreate.
    I picked up a huge pile of floppy disks from a seller on facebook recently. I noticed there were dozens of them that had a hole drilled in them so they could be formatted as HD. I was going to toss them, because I don't really want to use them like they are, but after reading this, perhaps they can be saved? I've got plenty of NOS DD and HD 3.5" disks, so I don't really need to save them, but I hate the idea of creating more garbage if they can be of use. What do you use to bulk erase them? I remember when I was in college, the library had a audio cassette (or maybe it was video?) eraser that was used for checking in books. I guess it reset the little detection strip in the book. We always called it "ironing books" because that's what it looked like they were doing.

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    The old VHS videotape erasers could do an acceptable job--you can also "roll your own" using magnets reclaimed from a scrap magnetron used in a microwave oven (I've posted on this).

    This video from 2009 shows the use of a Radio Shack VHS tape eraser.

    But forget about the disks with the hole punched in them--they hail from a time when HD media was significantly more expensive than DD stuff, so it was a cheapskate's way of making HD diskettes--they probably won't work for long anyway.

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    Quote Originally Posted by Chuck(G) View Post
    You could punch a density hole in the 720K disks written as 1.44M and read them on a standard drive--for awhile anyway.
    I did that to a few disks that were formatted the wrong way so the data could be read off, but my policy was the disk went in the garbage afterwards.
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    Chuck, out of curiosity, what brands of disks were these that experienced the failures? Were there any known issues with how they were stored?

    I've still got a bunch of bulk-no-name 720k that I formatted HD back in the day, and the ones I have tested recently were still fine. I'm not saying that even a single person on this planet other than myself would have any luck with that - I formatted, tested, re-tested, double checked, and re-checked every one of my disks to make sure they would hold data to my satisfaction. Few others would have even run Disk Test after copying a file.

    I wonder if some brands or even lots may have been better or worse for this purpose than others.

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    Oh, I suspect that there was a considerable amount of brand-dependency, given the wide variation in coating formulation.

    The sample in question is unbranded, but carries a Nashua sticky label.

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    A valuable PSA, Chuck. I found this out myself trying to trade software with a friend who owned a PS/2 Model 30-286. I have that same model in my collection just to prove that I wasn't going crazy, and that IBM (of all people) weren't honoring the density hole. (Why?!?)

    I remember the magazine adverts for the DSDD hole punch: "We wrote to this disk every minute for a week and it read back EVERY TIME!" Yes, well, try reading it back after only 6 months and see how many bits have flown away.

    I saved money on the punch by burning the hole with a soldering iron through the plastic. Today I can't read any of those disks, and just cover up the hole and reformat them when I see them. I did later get a 3.5" punch, only because I wanted my 5.25" punch to have a companion.
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    The big sinking feeling comes when I get asked, "well, how much of the (30 year old) data can you recover?".

    About 25-30% as a rule. The clients don't like that answer, but what are you going to do? I can appreciate the feeling that a dentist gets when talking to a patient who's done DIY dentistry by plugging his cavities with super glue.

    I think that the issue is more particle size and coating thickness than coercivity. I used to have a chart from NML (and there's probably one on the web) of the various characteristics of the cookie dough used on HD and DD microfloppies.

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