Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!tut.cis.ohio-state.edu!snorkelwacker!think!zaphod.mps.ohio-state.edu!usc!ucsd!helios.ee.lbl.gov!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: 19 Jan 90 17:45:03 GMT References: <3226@ucrmath.UCR.EDU> <7715@nigel.udel.EDU> <4407@pegasus.ATT.COM> Organization: University of Utah CS Dept Lines: 28 In-reply-to: psrc@pegasus.ATT.COM's message of 18 Jan 90 17:53:05 GMT In article <4407@pegasus.ATT.COM> psrc@pegasus.ATT.COM (Paul S. R. Chisholm) writes: >In article , jacobs@cs.utah.edu >(Steven R. Jacobs) writes: >> 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. > >Nope; a 1.44M drive has twice the number of sectors per track, but the >same number of tracks (of the same width and density) as the 720K. Yes, I really blew it on this point. >> 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). > > A 1.2M disk has exactly twice as many sectors per track, and twice as > many (narrower) tracks, as a 360K disk. This would mean that the high density disks are 1.44M instead of 1.2M would it not? I believe the high density disks are 15 sectors/track while the 360K disks are 9 sectors/track. This, with twice as many tracks on the 1.2M floppies, accounts for the 1.2M size. > Paul S. R. Chisholm, AT&T Bell Laboratories -- Steve Jacobs ({bellcore,hplabs,uunet}!utah-cs!jacobs, jacobs@cs.utah.edu)