Floppy disks again

From: Clint Wolff <vaxman_at_uswest.net>
Date: Tue Oct 12 19:55:45 1999

On Tue, 12 Oct 1999 allisonp_at_world.std.com wrote:

> > Ok, so 48 TPI media has low coercivity, so a 96TPI head with higher
> > write current will cause the adjacent tracks to erase because of
> > the magnet fringes from the head. These magnetic fringes aren't
> > strong enough to effect 96TPI media because it has a higher
> > coercivity.
>
> ???? reread that and see if it makes sense to you...
>

Ok, so not as much as at 7:00 this morning... HD media has a higher
coercivity, thus requires more write current to put a bit on the
disk. If you use that much write current with LD media (lower
coercivity) you will get a larger bit. The larger bit will partially
overwrite adjacent bits, leading to low amplitude, and read errors.

> There are two media for 96tpi, one for DD and lower and is the SAME
> magnetic material as 48tpi. THere is also the 1.2mb media and this is
> VERY DIFFERENT and incompatable with any other drive or density.
>
> So if we ignore 1.2mb media and the oddbal spindle speeds and data rates
> that go with it we come down to one media (softs sector) and 6 different
> drives over the years. They are:
>
> 48tpi single sided (sa400)
> 48tpi double sided (sa450)
> 96tpi single sided (teac Fd55E or DEC RX50)
> 96tpi double sided (teac FD55F)
> 100tpi single and double sided models (micropolis I think)
>

Ok, I wasn't aware of any 96tpi drives except the HD ones... Were
they ever used in the PC marketplace, or was it mostly a DEC thing?
After re-reading my uVAX manual about the RX50, I agree it is a
96tpi single sided drive, though the manual says: "Use only formatted
RX50 diskettes, available from DIGITAL or its licensed distributors"

So there are four drives using the same media:
SSDD 180K,48tpi,40tracks/side
DSDD 360K,48tpi,40tracks/side
RX50 360K,96tpi,80tracks/side
???? 720K,96tpi,80tracks/side - What was (is) this called? DSQD?

And the HD drive:
DSHD 1.2M,96tpi,80tracks/side - can read older media, but writing
                                   is unreliable (head isn't wide
                                   enough to erase the whole old track)

If Bill indeed has DSDD media, bulk erasing the media before applying
it to the 96tpi (non-HD) drive should work fine. This erases the old
data from between the new (half as wide) tracks, so it doesn't
interfere with reading.

>
> Allison
>

clint
Received on Tue Oct 12 1999 - 19:55:45 BST