robs@ux1.cso.uiuc.edu (Rob Schaeffer) (02/22/91)
Can a high density drive be made to read a high density disk
that was formatted in a low density drive?
Hopefully via. an Init.
E-Mail, I'll post a summary. Unless you WANT to post...
Thanks.
Rob
--
robs@ux1.cso.uiuc.edu
"My God, [static] it's full of [static] toasters..."
-- 2001, A Hardware Odysseyrobs@ux1.cso.uiuc.edu (Rob Schaeffer) (02/22/91)
robs@ux1.cso.uiuc.edu (Rob Schaeffer) writes: >Can a high density drive be made to read a high density disk >that was formatted in a low density drive? Umm, add to this that the disks in question will be used a lot and a simple piece of tape will most likely peal off. Rob -- robs@ux1.cso.uiuc.edu "My God, [static] it's full of [static] toasters..." -- 2001, A Hardware Odyssey
bskendig@burn.Princeton.EDU (Brian Kendig) (02/22/91)
In article <1991Feb21.211235.11051@ux1.cso.uiuc.edu> robs@ux1.cso.uiuc.edu (Rob Schaeffer) writes: >Can a high density drive be made to read a high density disk >that was formatted in a low density drive? In a word: no. A high-density disk formatted in a low-density drive is unstable; even low-density drives other than the one it was formatted in probably won't be able to read the disk. Here's the reason as I understand it (and more knowledgeable souls may want to throw in a correction here and there): A high density disk crams much more magnetized information into the same amount of space. Therefore, the disk has to be made more resistant to having its data changed, or else the disk will end up scrambling itself! A high density drive uses a more powerful electromagnetic field to deal with the more resistant HD disks. So: If you format a high density disk in a low density drive, then in an ideal world, it should either format fine, or not at all because the low density drive field isn't strong enough to change the information. But in the real (?) world, it turns out that the slight imperfections in the disk and in the drive combine to affect some parts of the disk but not others, so the disk may become weakly formatted. Put this disk into any other drive, and it's like trying to fit the wrong puzzle-pieces together. If you format a low density disk in a high density drive as high density, then the disk will be treated with a much-too-powerful electromagnetic field. When you set one bit of information, you'll probably end up erasing four or five nearby bits. Note that high density drives can recognize and deal with low density disks as low density; they can reduce their field strength. I've also heard rumors that once you format a HD disk as DD (double density, or low density -- the SD single density disks went out of style years ago), you can never reformat it as HD again; the format always fails Or something like that. (Can anyone clarify this?) And I'd assume that the 2.88M ED disks behave in a similar way to all this. I hope I've cleared things up somewhat. << Brian >> | Brian S. Kendig \ Macintosh | Engineering, | bskendig | | Computer Engineering |\ Thought | USS Enterprise | @phoenix.Princeton.EDU | Princeton University |_\ Police | -= NCC-1701-D =- | @PUCC.BITNET | "It's not that I don't have the work to *do* -- I don't do the work I *have*."
tchi@sal-sun9.usc.edu (The Answer Company) (02/22/91)
In article <6481@idunno.Princeton.EDU>, bskendig@burn.Princeton.EDU (Brian Kendig) writes: |> In article <1991Feb21.211235.11051@ux1.cso.uiuc.edu> robs@ux1.cso.uiuc.edu (Rob Schaeffer) writes: |> >Can a high density drive be made to read a high density disk |> >that was formatted in a low density drive? |> |> In a word: no. A high-density disk formatted in a low-density drive |> is unstable; even low-density drives other than the one it was |> formatted in probably won't be able to read the disk. |> |> Here's the reason as I understand it (and more knowledgeable souls may |> want to throw in a correction here and there): |> |> A high density disk crams much more magnetized information into the |> same amount of space. Therefore, the disk has to be made more |> resistant to having its data changed, or else the disk will end up |> scrambling itself! |> |> A high density drive uses a more powerful electromagnetic field to |> deal with the more resistant HD disks. |> |> So: |> |> If you format a high density disk in a low density drive, then in an |> ideal world, it should either format fine, or not at all because the |> low density drive field isn't strong enough to change the information. |> But in the real (?) world, it turns out that the slight imperfections |> in the disk and in the drive combine to affect some parts of the disk |> but not others, so the disk may become weakly formatted. Put this |> disk into any other drive, and it's like trying to fit the wrong |> puzzle-pieces together. |> |> If you format a low density disk in a high density drive as high |> density, then the disk will be treated with a much-too-powerful |> electromagnetic field. When you set one bit of information, you'll |> probably end up erasing four or five nearby bits. |> |> Note that high density drives can recognize and deal with low density |> disks as low density; they can reduce their field strength. |> |> I've also heard rumors that once you format a HD disk as DD (double |> density, or low density -- the SD single density disks went out of |> style years ago), you can never reformat it as HD again; the format |> always fails Or something like that. (Can anyone clarify this?) |> |> And I'd assume that the 2.88M ED disks behave in a similar way to all |> this. |> |> I hope I've cleared things up somewhat. |> |> << Brian >> |> |> | Brian S. Kendig \ Macintosh | Engineering, | bskendig | |> | Computer Engineering |\ Thought | USS Enterprise | @phoenix.Princeton.EDU |> | Princeton University |_\ Police | -= NCC-1701-D =- | @PUCC.BITNET | |> "It's not that I don't have the work to *do* -- I don't do the work I *have*." Hmmm... From what I remember, the magnetic field strengths are the opposite from what Brian mentioned (ie. the low density drives have a higher field strength than the high density drives). The high density disks are more expensive because it is harder to make magnetic media that requires LESS field strength to write data to the disk. Therefore if one puts a hole in the DD disk and try to pass it off as a HD disk in a high density drive, the high density drive does not have enough field strength to writ e data to the disk so when you try to read the data the next time, boom! I used to work at ASUCLA's graphic services where we rent time on the Macintosh. I've had no problems with people using HD disks in low density drives (ie. Plus, old SE, and Mac II) as long as the disk is formatted in a low density drive (obviously) and they didn't use the disk in a high density drive. Again, the HD drives can read data from a DD disk since the HD head is more sensitive (ie. needs less field strength to distinguish ones and zeros) but the data is written a too low of a field strength for the DD head to pick it up. Maybe the HD drive recognized that a HD disk is in the drive and uses less power to write data and when a DD disk is in the drive, it steps up the juice to write to DD disks. Anyways... I was told all this by some Apple Certified Techs at the ASUCLA Computer Store awhile back. Hopefully what I've said (wrote) is correct. My solution is to stick with DD disks and not worry about the lost 650K and so far I've had no problems using them in a IIcx and a SE/30. Of course I only have a Mac Plus so I don't really have a choice... :) Sorry the message is so verbose... Tony Chi (tchi@usc.edu) The Answer Company: typesetting, graphic design, Macintosh consulting I'm getting my Masters in EE just for fun...
mkelly@cs.uoregon.edu (Michael A. Kelly) (02/22/91)
In article <6481@idunno.Princeton.EDU> bskendig@burn.Princeton.EDU (Brian Kendig) writes: > >If you format a low density disk in a high density drive as high >density, then the disk will be treated with a much-too-powerful >electromagnetic field. When you set one bit of information, you'll >probably end up erasing four or five nearby bits. > I've been doing this for almost two years now, and haven't had any problems. (Not that I don't believe you.) I'm a poor starving student and can't afford the _real_ HD disks, so I just put a hole in the corner of a DD disk, and voila! (I'm using a IIcx, if that matters.) Mike. -- _____________________________________________________________________________ Michael A. Kelly America Online: Michael792 mkelly@cs.uoregon.edu Compu$erve: 73567,1651 _____________________________________________________________________________
laszlo@hppad.waterloo.hp.com (Joe Laszlo) (03/01/91)
I've been using DD disks as HD disks for a while too... so far one disk
wouldn't format so I used it as an 800K (and it is fine).
High density drives use _lower_ field strengths - that's how more data can
be put on the disk - the density is higher, so the data takes less area.
(think of a low density track being twice as wide as a high density track if
you like that's :-)
Does anybody know where to get a 3.5" disk hole puncher? ( A good one; I
remember using a single-hole punch for 5.25" disks in the old days... some
machines used the timing hole and you had to open cut/force open the disk,
take the floppy out, punch a symmetric timing hole, replace the floppy and
tape the disk shut... )
---------------------------------
laszlo@waterloo.hp.com
jflaszlo@sunee.waterloo.edu
---------------------------------daveh@ccwf.cc.utexas.edu (David H. Huang) (03/01/91)
In article <15110001@hppad.waterloo.hp.com> laszlo@hppad.waterloo.hp.com (Joe Laszlo) writes: > >I've been using DD disks as HD disks for a while too... so far one disk >wouldn't format so I used it as an 800K (and it is fine). [ ... ] >Does anybody know where to get a 3.5" disk hole puncher? ( A good one; I >remember using a single-hole punch for 5.25" disks in the old days... some >machines used the timing hole and you had to open cut/force open the disk, >take the floppy out, punch a symmetric timing hole, replace the floppy and >tape the disk shut... ) How are you using DD disks as HD disks without the 3.5" hole puncher? Apple 5.25"s didn't use the timing hole, so you didn't have to go through all that fuss with opening the disk. I always used some sharp scissors and another disk to get the write protect notch in the right place... I guess that's what you get from using IBM :-) (just kidding! Put that flamethrower away!! I don't know if IBM drives use the timing hole or not, but I think they do). >--------------------------------- > laszlo@waterloo.hp.com > jflaszlo@sunee.waterloo.edu >--------------------------------- -- David Huang | Internet: daveh@ccwf.cc.utexas.edu | "Slight accidents with funny rays UUCP: ...!ut-emx!ccwf.cc.utexas.edu!daveh | can have serious consequences" America Online: DrWho29 |
laszlo@hppad.waterloo.hp.com (Joe Laszlo) (03/03/91)
> How are you using DD disks as HD disks without the 3.5" hole puncher? I use my trusty soldering iron with a small fan by a large window... stinks bigtime. :( > Apple 5.25"s didn't use the timing hole, so you didn't have to go > through all that fuss with opening the disk. I always used some sharp > scissors and another disk to get the write protect notch in the right > place... > I guess that's what you get from using IBM :-) (just kidding! Put that > flamethrower away!! I don't know if IBM drives use the timing hole or > not, but I think they do). no flames, but I use a PC only at gunpoint. (or when school demands :)