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Thread: 5.25" floppy disks with bad sectors - any solutions?

  1. #31

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    Quote Originally Posted by kishy View Post
    I'm not sure I want to try an unconditional format...if it is refusing to do it, wouldn't that possibly result in drive damage if the drive was instructed to, for example, seek to a location it doesn't know how to seek to (for example smash the r/w heads into something internally)? Obviously that's less catastrophic for a floppy drive which moves slowly compared to a hard drive, but still not good.
    You are misunderstanding something there:

    An unconditional format aren't dangerous to the drive at all. The only difference betwen unconditional format and normal format is that normal format tries to verify/write to the existing disk layout while an unconditional format will rewrite the disk layer before starting a normal format. Because of this, "un-format" information can't be saved to the disk, and in cause you had some imporiant files on the disk when it was "accidentally" formated, you won't be able to restore them.

    Of course you are not trying to "accidentally" format any of the disks, so an unconditional format is totally safe in your cause.

    (the R/W head of the floppy drive slides on a rail. When it reaches the end of this rail, the head can't possibly move any futher. And, when it comes to floppy disks, the heads are touching the surface of the disks all the time, soyou don't have to worry about disk carsh.)
    Last edited by per; September 13th, 2009 at 02:17 PM.
    Current systems owned by me:
    Vintage:IBM PC/XT submodel 087 ( 1983 ), [Kon]tiki-100 rev. C (1983), Compaq Portable I ( 1984 ), IBM PC/XT submodel 078 ( 1985 ), IBM PC/XT286 ( ~1986 ), 3x Nintendo Entertainement Systems ( 1987 ).
    Obsolete:Commodore A500 ( ~1990 ), IBM PS/2 model 70/386 type 8570-161 ( 1991 ), Atari Lynx II ( ~1992 ), Generic Intel 486SX PC ( ~1993 ), AT/T Globalyst Pentium w/FDIV bug MB ( 1994 ), Compaq 486DX4 laptop ( ~1995 ).

  2. #32

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    Quote Originally Posted by per View Post
    You are misunderstanding something there:

    An unconditional format aren't dangerous to the drive at all. The only difference betwen unconditional format and normal format is that normal format tries to verify/write to the existing disk layout while an unconditional format will rewrite the disk layer before starting a normal format. Because of this, "un-format" information can't be saved to the disk, and in cause you had some imporiant files on the disk when it was "accidentally" formated, you won't be able to restore them.

    Of course you are not trying to "accidentally" format any of the disks, so an unconditional format is totally safe in your cause.

    (the R/W head of the floppy drive slides on a rail. When it reaches the end of this rail, the head can't possibly move any futher. And, when it comes to floppy disks, the heads are touching the surface of the disks all the time, soyou don't have to worry about disk carsh.)
    Oh, that's good to know then...thanks. I do know the head is on a rail, but I wasn't sure if it's possible to knock things out of alignment.

    However, in this case, isn't it true that even an unconditional format won't format the disks to 720k, since the format command doesn't actually support 720k 5.25" disks?

  3. #33

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    Quote Originally Posted by kishy View Post
    As one of the replies after yours states it looks like the format command /f:720 refers exclusively to 3.5" 720k disks, which are far more common it would seem (I actually have some of them, bought them new when I was younger...3 out of the set of 10 still work).
    3.5" DD disks were much more widely used than you might think. Aside from PCs, they would include the MSX, Mac, Apple II, Lisa, Amiga, Atari ST, Commodore 1581 drives, HP 150, and also things like music synthesizers, embroidery machines, and word processors.

    Quote Originally Posted by kishy View Post
    I wonder...I have a few Super-I/O cards, I wonder if the floppy controllers on any of them support 720k 5.25" formatting. Something to investigate in the future...those cards are never as simple to set up as they appear.
    Since QD disks use the DD bitrate, any PC controller can use them. You just need an 80-track drive.

    Quote Originally Posted by kishy View Post
    I figured it might be something about that (720k 3.5" disks), but was hoping maybe the format command could use the same switch for either type. Apparently not.
    FORMAT can only use the disk types supported by DOS, which do not include 5.25" 720k.

    Quote Originally Posted by kishy View Post
    I've probably missed something in this thread, but are "QD" disks actually different physically, or is it simply the recording method that differs?
    It's just the recording method; there's no physical difference with DD disks. Usually, QD disks were tested more rigorously because it was thought that 80-track formatting was more demanding on the disk. I actually have two boxes of QD disks that I use on my 5150 as 360k disks.

    Most DD disks will format to 80 tracks with no problems, except perhaps for some no-name brands, which as Chuck mentioned, tend to have lower-quality media.

  4. #34

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    Quote Originally Posted by kishy View Post
    Oh, that's good to know then...thanks. I do know the head is on a rail, but I wasn't sure if it's possible to knock things out of alignment.

    However, in this case, isn't it true that even an unconditional format won't format the disks to 720k, since the format command doesn't actually support 720k 5.25" disks?
    There is almost nothing that can get the head out of alginment unless you drop the drive or physically alter the head manually.

    Well, as I said, an Unconditional format is simply a "low-level" format of the floppy disk, and absolutely all data (including the controll data) is being rewritten. Since your disks has been formated a way they weren't supposed to, the magnetic data is all mixed up and an Unconditional format is actually the only way to fix them.

    About 720KB 5.25" disks and the format utility, the format program isn't what's limiting your posibilities. when you format a disk while using the "/F:x" parameter, the Format utility checks with the BIOS to see if the drive actually IS what you specify. If the BIOS don't agree, you'll get an error. (I think. It may also check the drive itself without going through the BIOS.)

    However, there is one way to override this (IIRC), and that is to manually specify the number of heads/cylinders(tracks-per-head)/sectors into the format utility. This should override the BIOS, and hopefully format it to what you want.

    Just be aware that you can get into some problems by formating a 5.25" disk to 720KB. This wasn't/isn't usual for PC's, and many programs will either think that the disk is a 720KB 3.5" floppy or a 360KB 5.25" floppy.
    Current systems owned by me:
    Vintage:IBM PC/XT submodel 087 ( 1983 ), [Kon]tiki-100 rev. C (1983), Compaq Portable I ( 1984 ), IBM PC/XT submodel 078 ( 1985 ), IBM PC/XT286 ( ~1986 ), 3x Nintendo Entertainement Systems ( 1987 ).
    Obsolete:Commodore A500 ( ~1990 ), IBM PS/2 model 70/386 type 8570-161 ( 1991 ), Atari Lynx II ( ~1992 ), Generic Intel 486SX PC ( ~1993 ), AT/T Globalyst Pentium w/FDIV bug MB ( 1994 ), Compaq 486DX4 laptop ( ~1995 ).

  5. #35

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    I originally got a lot of information from Scott Mueller's Repair book. IIRC, it explains most of what I've seen here. Regarding physical writing of the disks, this Floppy Primer page explains, among other things, azimuth and radial alignment. I thought this might be of interest here.

    I've also had a lot of educational fun playing with different formats. Programs such as the MS format command obviously have their own agenda, but there are other programs out there which allow you the freedom to make your own choices. My favourite is FreeForm, a menu-driven floppy disk formatter. It's a 91K download from Simtel.Net. Look for ffrm231a.zip. Almost any combination of formatting parameters can be chosen using that program.

    Because of the menus, FreeForm is very educational (to me) but for a modern formatter I use, and recommend, the one from FreeDos. Look for FMT091v.ZIP here. It will let you specify tracks and sectors and, AFAIK it is written solely for the benefit of the users. It also has no licensing encumbrances.

    Didn't MicroSoft use 1.7Mb distribution diskettes at one point? I seem to recall that one purpose was that you couldn't copy them using MS's own software. Of course those were 3.5" diskettes, but I'm sure the same trick has been used for 5.25s. You can certainly format 1.2s to 1.4, although I notice that the reliability goes down.
    Last edited by Ole Juul; September 13th, 2009 at 03:45 PM.

  6. #36
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    Quote Originally Posted by kishy View Post
    Are there any specific advantages to the 5.25" 77 cylinder 100tpi format? I imagine it's useless without hardware support but interesting to know.
    None that I'm aware of; they were an early 5.25" format and there were comparatively few systems that used them. At Durango, we recorded GCR using a WD1781 controller and a whole bunch of glue ICs and got about 960K per 100 tpi 5.25" floppy. Had the 96 tpi drives been available, we would have happily used those instead--the Micropolis drives were glacially slow when it came to seeking.

    There are some small differences in the connector assignments, but generally the drives are electrically compatible with the PC floppy interface.

    Sort of an interesting evolutionary dead end, like 3.25" diskettes and Drivetec floppies.

    Quote Originally Posted by Ole Juul View Post
    Didn't MicroSoft use 1.7Mb distribution diskettes at one point? I seem to recall that the one purpose was that you couldn't copy them using MS's own software. Of course those were 3.5" diskettes, but I'm sure the same trick has been used for 5.25s. You can certainly format 1.2s to 1.4, although I notice that the reliability goes down.
    Both IBM and Microsoft used "extreme" formats. Google "DMF" and "XDF" formats--there's plenty of information out there on them. Both IBM and MS offered to send you conventionally-formatted floppies if you yelled loud enough.


    (I don't really collect either, but I have a ton of old stuff hanging around from having been in this racket for too long. Even if I could find the systems that I used when I was young, I couldn't afford to run them...)

  7. #37

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    There's pretty much too much stuff there for me to specifically address (I'm sure you all understand).

    Basically, I don't have any more questions...you've been that thorough

    About 1.7 DMF floppies - yes, MS used them for Win95 and possibly other releases on floppies. For the person today who may be trying to write those disks, I advise you to pick disks you won't care to lose...they will NOT be reliable when formatted back to 1.44 afterwards!

  8. #38

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    Quote Originally Posted by kishy View Post
    About 1.7 DMF floppies - yes, MS used them for Win95 and possibly other releases on floppies. For the person today who may be trying to write those disks, I advise you to pick disks you won't care to lose...they will NOT be reliable when formatted back to 1.44 afterwards!
    I doubt that the media is actually damaged and I'm fairly certain that the disc would be perfectly good if you wiped it. Of course if you don't have anything to do that with then there might be a problem, I don't know about that.

  9. #39

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    Quote Originally Posted by Ole Juul View Post
    I doubt that the media is actually damaged and I'm fairly certain that the disc would be perfectly good if you wiped it. Of course if you don't have anything to do that with then there might be a problem, I don't know about that.
    I'm referring to starting with a 1.44mb floppy disk, formatting it to 1.7 DMF for holding files during an install, then formatting back to 1.44 afterwards. Every disk I used in that set (I installed Win95 via floppies once just for the experience...what a waste) was trash afterwards. Basically, you'd format the disk back, put a file on it, then pop it in a few minutes later and the file is gone (or heavily corrupted).

  10. #40

    Default 1.7 to 1.44 OK

    I just took an old Mackintosh 3.5" disk which, of course, wouldn't read on a DOS system. Then I formatted it to 1.7M and wrote a file to it and ran chkdsk. All was fine. Then I formatted it to 1.4M and wrote a file to it and ran chdsk. All is still fine! It is indeed possible to format to 1.7 and then go back to 1.44. This was all done in the drive and I did not need to remove the disk to wipe it.

    The program I used was FreeForm v2.31. I tried reformatting with FreeDos Format v1.0 and it appeared to work but upon writing a file or running chkdsk it complained. So, it looks like it all depends upon the formatting program.

    I have heard people complaining about inadequacies of the MS format program, but I am surprised that the FreeDos program has the same bug. However, I am not completely sure that the FreeDos program would not be able do it if given the correct parameters. It has several ways of using it. FreeForm is just a no-brainer that's why I used that.

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