chris@genly.UUCP (Chris Hind Genly) (06/17/91)
I'd like some help understanding the various types of floppies. I have a
really old machine at home, an 8088, with a 5 1/4 inch floppy drive that
works with DS DD disks. I'm running PCDOS 2.10. I tried to format a 5 1/4
inch DS HD floppy on my machine and I got an error message along the lines of
'track 0 unwritable.' The two types of floppies appear identical to the eye.
I assumed that I'd be able to format the HD floppy as a DD floppy and just
waste the bandwidth.
1) Why can't I format a DS HD diskette as a DS DD disk?
2) Is there a slot or hole somewhere in the floppy jacket that tells
the drive what capacity disk is inserted?
2) What are the various diskette formats available now, and what
are thier capacities?
Thanks in advance.
* * *
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/ Chris Hind Genly chris@genly.uucp uunet!hsi!genly!chris \
----------------------------------------------------------------cctr132@csc.canterbury.ac.nz (Nick FitzGerald, CSC, Uni. of Canterbury, NZ) (06/18/91)
In article <chris.3717@genly.UUCP>, chris@genly.UUCP (Chris Hind Genly) writes: > I'd like some help understanding the various types of floppies. I have a > really old machine at home, an 8088, with a 5 1/4 inch floppy drive that > works with DS DD disks. I'm running PCDOS 2.10. I tried to format a 5 1/4 > inch DS HD floppy on my machine and I got an error message along the lines of > 'track 0 unwritable.' The two types of floppies appear identical to the eye. > I assumed that I'd be able to format the HD floppy as a DD floppy and just > waste the bandwidth. > > 1) Why can't I format a DS HD diskette as a DS DD disk? Assuming that you do not have a diskette that has a genuinely "bad" spot on track 0 (referred to below as the first track), the following may be useful: I seem to remember (vaguely) that DOS used to be fussy about formatting already formatted diskettes to a _different_ format than they were already formatted to. Eg. A DS DD formatted to 320K would not be re-formatted to 360K, but to 320K. _Most_ (OK, so yours doesn't! _I_ am yet to see one that don't) DD drives accurately read the first track of both DD and HD disks (you can usually do a DIR listing of a HD, but trying to TYPE, COPY or execute the files results in a "Sector not found" error, or less often, a "Bad sector" error. My guess is that the HD diskettes are pre-formatted and the DOS FORMAT prog is reading the media-descriptor byte from the FAT OK (cause it's on that first track). This tells FORMAT the disk format to use, and something is going wrong from there - the error message may itself be erroneously identifying the source of error. (I doubt that DOS 2.10 knew anything about HD 5 1/4's, so may be spitting over the 1.2M media- descriptor value it gets - it make "err on the side of caution", suspecting that it is actually a non-DOS disk and the "unwritable" message would be something of a warning.) Now, I'm not sure if this "problem" with FORMAT being "bloody minded" about this sort of thing is in later versions of DOS or not, so trying on a PC with a more recent DOS may do the trick, or use a third-party FORMAT routine (eg. the one in PC-Tools formats to what you select, regardless of what's already there). > 2) Is there a slot or hole somewhere in the floppy jacket that tells > the drive what capacity disk is inserted? Not with 5 1/4's for DOS-like machines (that I've ever seen - to be on the safe side 8-) ). > 2) What are the various diskette formats available now, and what > are thier capacities? What school did you go to? 1, 2, 2 ?? 8-) But seriously: I think this has already been answered in another post. --------------------------------------------------------------------------- Nick FitzGerald, PC Applications Consultant, CSC, Uni of Canterbury, N.Z. Internet: n.fitzgerald@csc.canterbury.ac.nz Phone: (64)(3) 642-337
dj@ctron.com (DJ Delorie) (06/18/91)
In article <chris.3717@genly.UUCP>, chris@genly.UUCP (Chris Hind Genly) writes: > 1) Why can't I format a DS HD diskette as a DS DD disk? The HD drive lays down two skinny tracks where the DD drive lays down one fat one. The DD drive isn't capable of erasing the two skinny HD tracks, as it misses one. This left over track does interfere with the read operation, as it's close enough to the head for that. You can reformat HD floppies as DD if you bulk erase them first, to erase all the skinny HD tracks. For this same reason, a 360K floppy written with a 1.2M drive cannot be reliably read on a 360K drive, as the track written is too skinny for the fat DD head in the drive. And a 360K floppy formatted with a 360K drive cannot be reliably written with a 1.2M drive, as the HD head is too skinny to erase the fat DD track. > 2) Is there a slot or hole somewhere in the floppy jacket that tells > the drive what capacity disk is inserted? Only on 3.5" floppies. The presence of the hole indicates a 1.44M disk. > 3) What are the various diskette formats available now, and what > are thier capacities? 8" : Your guess is as good as mine, but I think some of the 5.25" formats are supported. 5.25" : 160 (SS/DD 8spt) 180 (SS/DD 9spt) 320 (DS/DD 8spt) 360 (DS/DD 9spt) 640 (DS/QD 8spt) * 720 (DS/QD 9spt) * 1.2 (DS/HD 15spt) 3.5" : 720 (DS/DD 9spt) 1.4 (DS/HD 18spt) 1.6 (Sun workstations) 2.8 (?) * Not IBM standard, but I can read them on my IBM clone, and some Z100's use this format. DJ dj@ctron.com
anthony@convex.csd.uwm.edu (Anthony J Stieber) (06/19/91)
In article <1991Jun18.050747.26870@bronze.ucs.indiana.edu> rschmidt@copper.ucs.indiana.edu (roy schmidt) writes: >Chris Genly writes: >> 1) Why can't I format a DS HD diskette as a DS DD disk? >> > The DS HD diskette uses a different type of medium for recording. It >is designed to hold a weaker magnetic "charge" for each bit written so Actually it's the reverse of that. HD disks of both sizes have a higher coercivity magnetic medium. This means the write current has to be higher, not lower. Trying to format a HD disk to DD may fail as the write current may not be high enough to write data reliably. Coercivity for 5.25" HD is about double that for DD. Try to format a DD disk as HD may fail as bit density is too high, and it lacks the coercivity to retain the magnetic field. In practice either can be swapped for the other, results will vary based on the drive and floppies used. In general, it's a good idea to not cross format HD and DD disks. I've only done it under duress. >> 2) Is there a slot or hole somewhere in the floppy jacket that tells >> the drive what capacity disk is inserted? > > Not on the 5-1/4" disks. The difference in medium is only important In recent years HD floppies almost never have a hub ring, will DD always do. In the past this was not true, so it's certainly possible to find a DD disk without a hub ring. As far as a I know, no drive can detect a hub ring. -- <-:(= Anthony Stieber anthony@csd4.csd.uwm.edu uwm!uwmcsd4!anthony Psion Mailing List subscriber submissions psion ----------\ the (human) moderator psion-owner -------+--@csd4.csd.uwm.edu subscriptions and file requests psion-request ----/
boyd@cs.unca.edu (Mark Boyd) (06/19/91)
While the difference in coercivity is large for 5.25 inch disks, about a factor of two if I recall correctly, the difference is on the order of 10 % for 3.5 inch disks. I suspect that is within manufacturing tolerances! If you try to format a 360 K to 1.2 M, you will get lots of bad blocks, almost all on the inner tracks. If you try to format 720 K as 1.44, you will get good disks. That is my experience and the experience of everybody I know who has tried it. Mark PS I find that my swiss army knife makes an adequate 720K to 1.44M disk converter. Of course I consider my swiss army knife to be the ultimate tool!
pshuang@athena.mit.edu (Ping-Shun Huang) (06/19/91)
You've gotten a good bunch of replies. More comments: In article <chris.3717@genly.UUCP> chris@genly.UUCP (Chris Hind Genly) writes: > The two types of floppies appear identical to the eye. That's not quite true, at least not with the diskettes which I have experience with (specifically, most of them are either brand name or from the mail order company MEI). If you hold them up so that light glares across the disk surface, you can see that the high density disks have a bluish tinge and are a lighter color than the brownish double-density floppies. I would disagree with <rschmidt> in that a HD should be able to be formatted as a DD. Since the two kinds of disks are made with different materials with different magnetic coercivities, you can neither format a high-density to low-density nor low-density to high density. The low-density drive is *NOT* indifferent to the medium. Like you, I have had no success getting my (Teac) low-density drive to format high-density medium. Also, I think a high-density drive uses a more powerful but also more focused magnetic flux in its heads, not less. <cctr132> is incorrect about HD diskettes being preformatted, because they are not, unless you pay through the nose for the special ones which have been. The DOS-FORMAT program as a general rule does not check the disk to see what density it is; it only checks the BIOS for the drive type and any relevant command line switches. (This can be verified with one of several TSR DOS function snoopers, which show DOS calling the BIOS format disk option with the appropriate number of sectors for the format selected without ever reading from the disk.) Many third-party replacements for FORMAT.COM, such as the ones which come with Norton or with PC-Tools, have a quick-format option which does always format a floppy which already been previously formatted to the same capacity. With this option, they do not do true formatting at all, but merely wipe the directory and the FAT tables for the diskette. -- Singing off, UNIX:/etc/ping instantiated (Ping Huang)
killoran@xn.ll.mit.edu (06/21/91)
Actually, many times one can tell a 360K disk from a 1.2M disk. 360K disks (2S/2D) tend to have a strength ring around the hole in the middle while 1.2M disks (2S/HD) tend not to. Mike Killoran killoran@xn.ll.mit.edu
anthony@convex.csd.uwm.edu (Anthony J Stieber) (06/21/91)
In article <1991Jun18.234702.9028@bronze.ucs.indiana.edu> ntaib@silver.ucs.indiana.edu (Nur Iskandar Taib) writes: >>In recent years HD floppies almost never have a hub ring, will DD >>always do. In the past this was not true, so it's certainly possible >>to find a DD disk without a hub ring. As far as a I know, no drive > >I remember someone selling a gizmo for putting >on hub rings years ago. Me too. >Incidentally, why don't HD diskettes have hub >rings? You'll also notice that HD floppies I don't really know, I remember reading about how HD drives don't need them. It seemed to me that hub rings are there to protect the hub from dammage, perhaps someone out there knows the real reason? >rotate all the time, DD stop spinning between >reads or writes (for 5 1/4s, that is). They do? I just checked on an old AT here, and it only spins for a moment when a disk is first inserted, and on disk activity. I do know that some 8" floppy drives did spin all the time, a solenoid would push the heads against the disk only when transfering data, to reduce disk and head wear. I'm cross posting this to alt.folklore.computers. -- <-:(= Anthony Stieber anthony@csd4.csd.uwm.edu uwm!uwmcsd4!anthony Psion Mailing List subscriber submissions psion ----------\ the (human) moderator psion-owner -------+--@csd4.csd.uwm.edu subscriptions and file requests psion-request ----/
knudsen@cbnewsd.att.com (michael.j.knudsen) (06/21/91)
I guess I'm just lucky -- my old Compaq Portable II (286 AT) can format HD disks as DD and read/write them OK. So far. The guy who sold it to me told me the drive was HD 1.2 Meg, so I bought and scrounged some HD diskettes, and found oaut the hard way that I couldn't get more than 360KB on them. What tipped me off was trying one of Norton's quick formats on a used HD floppy -- of course that didn't work. However, raw DOS format of a virgin HD seems to work, tho I shouldn't take a chance on this with valuable data. I shouldn't have much trouble trading a couple boxes of HD flops for the same number of DD floppies :-) -- "What America needs is A Thousand Points When Lit..." knudsen@ihlpl.att.com
afdenis@lims05.lerc.nasa.gov (Stephen Dennison) (06/29/91)
In article <13264@uwm.edu>, anthony@convex.csd.uwm.edu (Anthony J Stieber) writes... >In article <1991Jun18.234702.9028@bronze.ucs.indiana.edu> ntaib@silver.ucs.indiana.edu (Nur Iskandar Taib) writes: >>Incidentally, why don't HD diskettes have hub >>rings? You'll also notice that HD floppies > >I don't really know, I remember reading about how HD drives don't >need them. It seemed to me that hub rings are there to protect >the hub from dammage, perhaps someone out there knows the real reason? > One possible explanation I heard is that HD disketts have their magnetic media impregnated to thicker mylar disks for stability. The reasoning was that the hubrings "thicken" the DS DD disks for positive clamping, and the HD disks, being thicker initially, don't require them. Could be BS but it made sense to me. "My life is a sine wave. Now, if I could just get the damned amplitude down..." Stephen Dennison