3B1<->3B2

[Bill Kennedy]

In article <2328 at cuuxb.ATT.COM> fmcgee at cuuxb.UUCP (Frank W. McGee) writes:
>In article <598 at whizz.uucp> bbh at whizz.uucp (Bud Hovell) writes:
>>In article <7047 at ihlpf.ATT.COM>, gmark at ihlpf.ATT.COM (Stewart) writes:
>>> What are the compatibilities between the 3B1 and 3B2?  File
[ ... ]

>>My understanding is that the 3b2 format is different than for the 3b1.
[ Frank suggests buying a package, I agree ]

>As for the 3b1 writing 3b2 disks, you'll have to have a different
>floppy drive to be able to do that (ie, a high density drive like they
>put in PC AT's).  The drives that come with the Unix PC have a
>formatted capacity of 360K max.  3b2 drives are a 720K format (so there

So far so good, but what Frank didn't say was that in order to fit 1.2Mb
on an AT style diskette they muck with the spindle motor speed.  It's my
understanding that the 3B2 uses a 96tpi drive like the AT and that the
reason that only 720K will fit is because the spindle motor speed remains
constant, thus only twice the capacity of a 40tpi drive.  On the outer
tracks there's some magnetic real estate that can be used by an AT type
drive that just isn't used because the rotational rate is constant.  If
it slows down, then more bytes can be fit on it.

This is nearly as much of a question as it is a statement.  I know, for
example, that "vanilla" 96tpi drives aren't compatible with the AT, nor
can you expect to get 15 sectors per track on the inner tracks of a
"vanilla" 96tpi drive.  Doesn't the AT type drive slow down on the inner
tracks to keep bits per inch about the same as on the outer tracks?

>is no amount of software that can be written that will allow a Unix PC
>to write a 720K disk).  However, if you've done the hardware mod to put
>a 1.2 MB drive in all you'll have to do is hack the device driver to
>allow the 720K format).  The 720K format is double-sided, quad-density,
>at 40 TPI if I remember right.

To be a hopeless nit picker, is it not 40 cylinders on 48tpi media and
80 cylinders on 96tpi media?

>Hope this helps you out,
>
>-- 
>Frank McGee
>Tier 3 Indirect Channel Sales Support
>attmail!fmcgee

Please don't flame if I'm mistaken, just post so we'll all know.
-- 
Bill Kennedy  usenet      {killer,att,cs.utexas.edu,sun!daver}!ssbn!bill
              internet    bill at ssbn.WLK.COM