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Newsgroups: comp.unix.bsd Path: sserve!manuel.anu.edu.au!munnari.oz.au!news.hawaii.edu!ames!saimiri.primate.wisc.edu!zaphod.mps.ohio-state.edu!magnus.acs.ohio-state.edu!csn!raven!rcd From: rcd@raven.eklektix.com (Dick Dunn) Subject: Re: [386BSD] ARGH! 720K 3.5" floppy support, anyone? Message-ID: <1992Dec11.073828@eklektix.com> Organization: eklektix - Boulder, Colorado References: <JKH.92Dec10090457@whisker.lotus.ie> <1992Dec10.215453.25586@fcom.cc.utah.edu> Date: Fri, 11 Dec 1992 07:38:28 GMT Lines: 38 jkh@whisker.lotus.ie (Jordan K. Hubbard) writes: >>...We need to assume that >>1.44MB also means 720K and that 1.2MB also equals 360K (though I'll >>admit to being a bit fuzzy on the later - do all 5.25" drives support >>360K?). 5.25" HD drives all support *reading* 360k...but... terry@cs.weber.edu (A Wizard of Earth C) writes: |A patch to "fix" this was posted some time ago. It's questionable in it's |utility, especially with regards to writing the floppies; this is (I've |heard) because there is a difference in the rotational speed on high vs. |low density disks, which basically requires you to blow a register to |set the speed. This makes it OK for reading, but unreliable at writing |and formatting ... Terry's got the wrong reason but definitely the write...er, right problem. 1.2 MB drives can read 360 KB floppies, but cannot write them reliably. The problem is one of read/write head design--simplifying somewhat, a 1.2 MB drive uses a narrower track than a 360 KB drive. If you write on a 360 drive, the 1.2 drive can read it just fine: it's got this narrow head cruising down the middle of a great wide data track. But if you try to *write* a 360 floppy on a 1.2 drive, you end up writing new data down the middle of the track but leaving old data on either side of it. A 1.2 drive *may* be able to recover this data--depends on drive design; I've had about half-and-half luck with the drives I've tested. A 360 drive is quite unlikely to read it at all. Remember, it's got a wider head, so it's getting a signal mixed from the old wide track and the new narrow track. (Apologies to disk-hardware types: I know I'm oversimplifying, but it's not too far off what's really happening.) I stumbled on this problem with SysV about once a year for several years. (Yeah, I'm a slow learner.:-) I finally solved it by making the /dev entries read/write for the 1.2 format and read-only for 360. -- Dick Dunn rcd@raven.eklektix.com -or- raven!rcd Boulder, Colorado ...Straight, but not narrow.