billlund@hpindwa.cup.hp.com (Bill Lund) (04/08/91)
I've noticed some odd behavior when using high density disks in a 800K drive. When formatted at 800K, it seems that the high density disks, which should be able to be formatted to 1.4M, have a high failure rate. In one case my Mac II couldn't format it at all. I had some of the high density disks sitting around and was going to use them as 800K formatted disks, but not if they are going to keep failing. Is there something particular to the high density disks that I'm not aware of? Thanks, Bill Lund HP Cupertino, CA
Charles.E.Dubuque@dartmouth.edu (Charles E. Dubuque) (04/10/91)
Using high density disks in an 800K drive is not like using Chrome cassette tapes in a tape deck meant for regular cassettes (which works fine but gives none of the advantages of Chrome). HD disks simply CANNOT be used as reliable 800K disks. I believe the problem is two-fold. Since HD disks have to store about 2 times as much information in the same surface area, I would imagine that: 1) the HD drive writes a signal that is of lesser strength than an 800K disk, otherwise it would destroy data. 2) that the HD disks are of a more sensitive medium than 800K disks, since it needs that extra sensitivity to pick up the weaker signal. Now, put a piece of Scotch tape over the HD disk and format it in a dumb 800K drive. It seems to work fine, but everytime you write, things start to get erased and overwritten, or mis-written or misread because (1) the 800K drive is writing a stronger signal to a more sensitive medium (2) the 800K drive is looking for a strong signal from a weaker signal medium. All this adds up to the problems you describe. Moral of the story: never use HD disks in 800K drives. It isn't meant to work that way (notice that Apple doesn't give you the option of formatting HD disks ar 400K,800K or 1.4M) Chuck ------------------------------------------------------------------------ Chuck Dubuque ||"It's one thing to think something that seems Dartmouth College || completely impossible. But quite another to HB 4233 Hanover NH || say it..." -- Silent Invasion, book II 03755 || C.Dubuque@Dartmouth.edu || DartmouthUs -not- the Review, but it's close ------------------------------------------------------------------------
rcook@ircsun1.ccmblab.nd.edu (Robert Kelley Cook) (04/11/91)
In article <1991Apr10.160835.5153@dartvax.dartmouth.edu>, Charles.E.Dubuque@dartmouth.edu (Charles E. Dubuque) writes: |> |> Since HD disks have to store about 2 times as much information in the |> same surface area, I would imagine that: 1) the HD drive writes a |> signal that is of lesser strength than an 800K disk, otherwise it would |> destroy data. 2) that the HD disks are of a more sensitive medium than |> 800K disks, since it needs that extra sensitivity to pick up the weaker |> signal. |> . . . |> |> All this adds up to the problems you describe. |> |> Moral of the story: never use HD disks in 800K drives. It isn't meant |> to work that way (notice that Apple doesn't give you the option of |> formatting HD disks ar 400K,800K or 1.4M) |> |> Chuck Actually, A high density disk needs a greater signal to flip the particles, because the medium used is magnetically less susceptible to spurious changes. They won't let you format high densitys as low density disks, because a low density drive doesn't nessecarily have the oomph to flip the bits of a high density disk even though it can read them. Robert Kelley Cook U. of Notre Dame '91
winders@aux.support.apple.com (Scott Winders) (04/12/91)
In article <1991Apr10.204450.8125@news.nd.edu> rcook@ircsun1.ccmblab.nd.edu (Robert Kelley Cook) writes: > In article <1991Apr10.160835.5153@dartvax.dartmouth.edu>, Charles.E.Dubuque@dartmouth.edu (Charles E. Dubuque) writes: >> >> Since HD disks have to store about 2 times as much information in the >> same surface area, I would imagine that: 1) the HD drive writes a >> signal that is of lesser strength than an 800K disk, otherwise it would >> destroy data. 2) that the HD disks are of a more sensitive medium than >> 800K disks, since it needs that extra sensitivity to pick up the weaker >> signal. >> > . . . >> >> All this adds up to the problems you describe. >> >> Moral of the story: never use HD disks in 800K drives. It isn't meant >> to work that way (notice that Apple doesn't give you the option of >> formatting HD disks ar 400K,800K or 1.4M) >> >> Chuck > > > Actually, A high density disk needs a greater signal to flip the > particles, because the medium used is magnetically less susceptible to > spurious changes. They won't let you format high densitys as low density > disks, because a low density drive doesn't nessecarily have the oomph to > flip the bits of a high density disk even though it can read them. > > Robert Kelley Cook > U. of Notre Dame '91 Not true Robert, Chuck is right. The coating on high density diskettes is thinner and has finer particles. This requires a less intense magnetic field from the read/write head to properly align the magnetic particles within the data cell during a write cycle. The magnetic field generated by Apple 800K and 400K drives is too strong and may cause data loss. Scott Winders internet: winders@aux.support.apple.com AppleLink: winders.s@applelink.apple.com
ldo@waikato.ac.nz (Lawrence D'Oliveiro, Waikato University) (04/12/91)
I don't know who's right about which type of disk uses the stronger magnetic fields, but I do know that, not only is it a bad idea to use a high-density disk in a double-density drive, but you're also going to have problems reformatting it in a high-density drive afterwards. The solution is to put the disk through a bulk eraser (or close to some other unshielded source of strong, oscillating magnetic fields) to completely wipe any trace of the incorrect formatting. Speaking of which, does anybody know of common, household items which can work (or be adapted to work) as a bulk eraser? Say, if I wave a disk about close to the compressor motor at the back of my refrigerator, or even the motors in my washing machine--would that work? Obviously, something that would only partially scramble the magnetic fields on the disk wouldn't be good enough; it's got to wipe it completely clean. Lawrence D'Oliveiro fone: +64-71-562-889 Computer Services Dept fax: +64-71-384-066 University of Waikato electric mail: ldo@waikato.ac.nz Hamilton, New Zealand 37^ 47' 26" S, 175^ 19' 7" E, GMT+12:00 Scientists on the verge of breakthrough: a longer-lasting light bulb that people _will_ have to keep on buying!
xdpq8@CCVAX.IASTATE.EDU (04/12/91)
the solution to the disk problem is quite simple:\ Use HD disks only in HD drives and use the DD ones in either one. Why would anyone want to use HD disks in a DD drive anyway??????? Steve Fuller xdpq8@isuvax.bitnet