ma168x@sdcc3.ucsd.EDU (John Wavrik) (10/30/86)
Several times in my life I have been in the position of listening to a
lengthy explanation of why it is impossible to do something I've already
done. I still don't know how to react.
According to the explanation recently given by John Plocher, it should
be impossible to do the following: write a track on a 360k drive, rewrite it
with a 1.2 meg, get a good read on the original 360. If one is to believe
the pictures, the 1.2 will record on only a small part of the 360k track --
so an attempt to read will produce a garbled mixture of new information from
the 1.2 and old from the original 360. I have no difficulty following the
theory!
When I recently acquired a Tandy 3000 someone suggested I get one of each
kind of drive. They gave essentially the same warning about track width.
I did not follow the advice -- I got two 1.2 meg drives even though I need to
exchange data with an older machine using 360k. I found it is fairly easy to
avoid having both machines write to the same disk -- but the recent postings
aroused my curiosity. I ran some tests using Forth (so I could be sure that the
same tracks were being used by both machines). I could not produce any problems
no matter what.
I think that anyone should use caution when writing to one disk with two
computers -- there is always the possibility that the heads on one machine are
mis-aligned. I can only report that there must be something wrong with a
theory whose predictions are not supported by experiment.
--J Wavrik
UCSDburton@parcvax.Xerox.COM (Philip M. Burton) (10/31/86)
As I've said before, with a 360 KB floppy drive costing only $100, it makes no sense to fool around, assuming that your work and your time have some value. Perhaps the reason that people have been lucky is that the source and target machines are at approximately the same temperature and humidity. Floppy disks are made from a poly-mumble-mumble film substrate that is notoriously non- uniform in expansion/contraction according to temp. and humidity. My own experience is that a Shugart (Panasonic) SA 455 has no trouble reading disks written on the 1.2 MB drive, but the Tandon in my XT at work just flat- out can't do it. Works fine with all disks from 360 KB drives. Phil Burton Xerox Corp.
ashok@softart.UUCP (Ashok C. Patel) (11/01/86)
> When I recently acquired a Tandy 3000 someone suggested I get one of each > kind of drive. They gave essentially the same warning about track width. > I did not follow the advice -- I got two 1.2 meg drives even though I need to > exchange data with an older machine using 360k. I found it is fairly easy to > avoid having both machines write to the same disk -- but the recent postings > aroused my curiosity. I ran some tests using Forth (so I could be sure that the > same tracks were being used by both machines). I could not produce any problems > no matter what. You got lucky. That's all. Whenever a track is written to the disk, there is no doubt some "magnetic leakage" written around where the track should be. If both drives are aligned just so *AND* the data separater in your controller was properly tuned, the weaker part of the 360k track (after being overwritten) would not be read and everything would look OK. If, however, your 1.2Meg and 360K drives were skewed in opposite directions, the "strong" signal written by the 1.2Meg drive would come in even weaker and that's where the trouble begins. I too have an AT and XT and for the first 6 months or so, I could transfer disks with no problem. After that, the drives became sufficiently skewed (It doesn't take much) and I could no longer read the disks reliably. I ended up buying the extra 360K drive for the AT. > I can only report that there must be something wrong with a > theory whose predictions are not supported by experiment. > --J Wavrik > UCSD It may be just that someone has oversimplified the theory for better understanding by those not "in the know" about such things. IBM would not have posted warnings time and time again (on *EVERY* scrap of paper that they publish about the 1.2Meg drives) if there was not indeed a promblem! It just isn't cost effective! I hope that this ends the discussion about what should have been a three or four message discussion! Ashok C. Patel Softart Microsystems Inc. -------------------------