Path: utzoo!attcan!uunet!mailrus!hellgate.utah.edu!hellgate!jacobs From: jacobs@cs.utah.edu (Steven R. Jacobs) Newsgroups: comp.sys.ibm.pc Subject: Re: Formatting 1.2 Meg disks to 360K question Message-ID: Date: 13 Jan 90 22:14:38 GMT References: <3226@ucrmath.UCR.EDU> <7715@nigel.udel.EDU> <25AD7F7A.26599@maccs.dcss.mcmaster.ca> Organization: University of Utah CS Dept Lines: 62 In-reply-to: cs4g6ag@maccs.dcss.mcmaster.ca's message of 12 Jan 90 06:55:53 GMT In article <25AD7F7A.26599@maccs.dcss.mcmaster.ca> cs4g6ag@maccs.dcss.mcmaster.ca (Stephen M. Dunn) writes: > In article jacobs@cs.utah.edu (Steven R. Jacobs) writes: >$>Having just had this problem, I asked around and it seems that High Density >$>disks and Double Density disks (used for 360k) do have physical differences. [[[On the High Density disks, there are only certain places for the sectors [[[while the DD's are more flexible since there's less stuff to squeze [[[together. >$The person that told you this was either joking or making it up to >$disguise their ignorance. The part that had sounded like a "joke" to me was the part the you conveniently deleted from the previous message (which I've added back in, highlighted by "[[[" above). I even _said_ in my message that the two disk types are physically similar (see below). But the part about "certain places for the sectors" is absurd, since the magnetic material covers the entire disk. Granted, the surface of the disk is polished (especially on the high density disks) but there are no "special" places on these particular disks. >$Physically, the two types of disks are ^^^^^^^^^^ >$similar, with oxide covering the entire surface of the disk. The ^^^^^^^ >$difference is in the oxide itself. On the high density disks, the >$oxide is a different material which requires a stronger magnetic >$field to record information. > That sure sounds like a physical difference to me. And also, as I > understand it, it's actually the other way round. A 1.2M disk actually > uses a weaker magnetic field, which makes 360K disks written in a 1.2M > drive unreadable in many 360K drives. I was not claiming that there were no physical differences, I only intended to claim that the physical differences were nothing like what the original poster had been told. Besides, if there were no physical differences then all disks would work in all drives. > If the problem was that 360K drive heads didn't generate strong enough > magnetic fields, then I should be able to format 1.2M floppies at 360K in > my 1.2M drive. Well, it doesn't work any better in that drive than it > does in my 360K drive. This would imply that 1.2M drives cannot write data on 360K disks, but people do this all the time. I've had no problem reading or writing 360K disks in 1.2M drives (this is not a good idea, however, since many 360K drives will have trouble reading data written by a 1.2M drive even if the floppy is formatted at 360K originally). The problem with formatting 1.2M floppies at 360K is the difference in the width of the recording heads. The recording heads for a 1.2M floppy are about 1/3 the width of the recording head in a 1.2M floppy. The 360K drives sometimes have trouble reading the narrow data path created by the 1.2M recording heads. Now I'm sure you will point out that the 1.44M microfloppy drives will format/read/write data at 720K. The reason that this works is that the data is _exactly_ twice as dense, so that the 1.44M drive can write the data on two neighboring tracks to make it look like 720K data. This is not possible with the 1.2M drive, since 1.2M is not an integer multiple of 360K (there are probably other complications as well). -- Steve Jacobs ({bellcore,hplabs,uunet}!utah-cs!jacobs, jacobs@cs.utah.edu)