vturner@dante.nmsu.EDU (Vaughan Turner) (11/28/89)
I heard somewhere that High Density Mac Disks shouldn't be used on a low density drive (400 or 800K). I kindof understand why this might be, but I was wondering if anyone could point me towards some technical information that confirms this (or not, I'd just like to know which it is). Any help would be appreciated, Vaughan -- Vaughan Turner BITNET: mcswvt@nmsuvm1.bitnet Box 3AT Computer Center INTERNET: vturner@nmsu.edu Las Cruces, NM 88001
phaedrus@blake.acs.washington.edu (the Wanderer) (11/28/89)
In article <VTURNER.89Nov27165819@dante.nmsu.EDU> vturner@dante.nmsu.EDU (Vaughan Turner) writes: >I heard somewhere that High Density Mac Disks shouldn't be used on a >low density drive (400 or 800K). I kindof understand why this might >be, but I was wondering if anyone could point me towards some >technical information that confirms this (or not, I'd just like to >know which it is). > >Any help would be appreciated, > Well, there are two reasons that I know/have heard of for not using HD disks in a normal drive (aside from the obvious one of wasting money... :) ). 1) I've talked to several people who theoretically know a lot about such things, and they say that the magnetic coating on the HD disks is not designed for the level/type of current that drives use in writing to the lower-density formats, and that more frequent I/O errors result. I've never run into this personally, but it's something you might want to consider if you're storing critical data. 2) Let's say you ignore 1), and initialize a high-density disk with a 400/800K format in a 400/800K drive. You then try to use said disk in a FDHD (high-density) drive. The Apple FDHD will steadfastly refuse to admit the possibility that an HD disk could conceivably be formatted in anything other than the HD format, and the Mac will give you the infamous "This disk is unreadable" dialog, even though the disk is fine. There is a way around this: just put a strip of dark tape over the square hole at the top-left corner of the HD disk. Of course, beware the usual hazards of tape getting stuck in your drive and disks getting stuck and other such catastrophes. >Vaughan >-- >Vaughan Turner BITNET: mcswvt@nmsuvm1.bitnet >Box 3AT Computer Center INTERNET: vturner@nmsu.edu >Las Cruces, NM 88001 -- Internet: phaedrus@u.washington.edu (University of Washington, Seattle) The views expressed here are not those of this station or its management. "If you can keep your head while those about you are losing theirs, consider an exciting career as a guillotine operator!"
vturner@dante.nmsu.EDU (Vaughan Turner) (11/29/89)
I have gotten several responses on how to *make* HD disks work as low density, and I appreciate the help. But what I was looking for is reasons *NOT* to do this. I work in a macintosh lab where *lots* of students want me to recover disks for them. If this could be minimized by not using HD disks as low density, that would make me happier. So, to clarify: I know you can use tape to fool the FDHD, but my question is: Can you do this without added fear of losing information off of the disk, and if so, why did Apple make the FDHD sensitive to the second hole, instead of letting you take your chances formatting a low density disk in a HD drive. Many people have commented on my using HD disks as low density disks and wasting money in the process. Although noone probably cares, I'm not the one who does this, but several of our users *do*. Our lab setting is a mixture of Plusses, SEs, SE/30s, and IIcxs, so HD problems will be a reality soon, I was just hoping to go into the fight well informed. Once again, any help appreciated, Vaughan -- Vaughan Turner BITNET: mcswvt@nmsuvm1.bitnet Box 3AT Computer Center INTERNET: vturner@nmsu.edu Las Cruces, NM 88001
legg@sirius.ua.oz.au (Christian Legg) (11/29/89)
Vaughan Turner (vturner@nmsu.edu) writes... >I heard somewhere that High Density Mac Disks shouldn't be used on a >low density drive (400 or 800K). I kindof understand why this might >be, but I was wondering if anyone could point me towards some >technical information that confirms this (or not, I'd just like to >know which it is). Well Vaughan, I believe the answer that you are looking for is a technical one. It is possible to format an HD disk in a Plus or SE (or similar 800k drive equipped Mac) and use it as a 400/800 k disc. However, if you then place this disk into a Mac with an HD disk drive it will try to read the disk as a 1.44 meg disk regardless. This is enforced by hardware - the Mac detects the extra hole in the disk and assumes that it is a 1.44 meg disk. Thus, it considers the 800k disk as faulty and gives you the option of formatting it. This problem could probably be overcome by blocking the high density hole, but then you may as well use normal 800k capable disks! Christian Legg ***************************************************************************** * Christian Legg, * * * University Computing Services, * 'Base 8 is just like base 10 really... * * University of Adelaide. * ...if you're missing two fingers.' * * * * * (08) 228 5549 * Tom Lehrer * * ACSnet : legg@sirius.ua.oz * * *****************************************************************************
allison@oyster.cis.ohio-state.edu (Mark Allison) (11/30/89)
Well Vaughan, I have been using HD disks in low density drives for a
couple of months now with no problems at all. I also know several
people who have used DD disks in SD drives, with no problems. The only
problem would be if you tried to format DD disks with HD format. 800K
would fit onto a 1.4M disk easily.
By the way, the reason I have been buying HD disks lately is that I am
anticipating buying an SE 30 (which of course comes with the HD drive)
and I don't want to waste any more money on 800K disks... all I will
have to do is copy the data off of the disks, then reformat them to get
the full 1.4M. I have tried this part too, and it works flawlessly.
Mark
--
Mark Allison - allison@cis.ohio-state.edu
"He who makes a beast of himself gets rid of the pain of being a man"
--- Hunter S. Thompson
-=-
"He who makes a beast of himself gets rid of the pain of being a man"
--- Hunter S. Thompsondatta@cpsc.ucalgary.ca (Slarti) (12/06/89)
In article <4658@blake.acs.washington.edu> phaedrus@blake.acs.washington.edu (the Wanderer) writes: > 2) Let's say you ignore 1), and initialize a high-density disk with a >400/800K format in a 400/800K drive. You then try to use said disk in a >FDHD (high-density) drive. The Apple FDHD will steadfastly refuse to admit >the possibility that an HD disk could conceivably be formatted in anything >other than the HD format, and the Mac will give you the infamous "This disk is >unreadable" dialog, even though the disk is fine. There is a way around this: >just put a strip of dark tape over the square hole at the top-left corner of >the HD disk. Of course, beware the usual hazards of tape getting stuck in >your drive and disks getting stuck and other such catastrophes. I have found that if you put the 800K formatted HD disk in a SuperDrive, you get the unique "This disk is incorrectly formatted for this drive" error message, and this appears to be the only case where that message occurs, so you can tell what's going wrong. I have also found (this could be my imagination) that if I format HD disks low-density, they sometimes refuse to reformat in an HD format and are thus basically trashed.... I have no idea why this occurs or if it is caused by the 800K format, but it is something to think about.
user7@amdcad.AMD.COM (Unix class) (12/07/89)
>I have also found (this could be my imagination) that if I format HD disks >low-density, they sometimes refuse to reformat in an HD format and are thus >basically trashed.... I have no idea why this occurs or if it is caused by the >800K format, but it is something to think about. If this is purely a software problem(i.e. it's because the 800K formatting left some garbage info behind) and not a hardware prob (damaged the disk physically) then try formatting it on an IBM drive as a 1.44m (or 720k?) and then reformat it on the mac. Basically, you want to remove whatever garbage the 800k formatter left behind. -Chung