13 Oct
1999
13 Oct
'99
6:21 a.m.
On Wed, 13 Oct 1999, Pete Turnbull wrote:
On Oct 12, 18:55, Clint Wolff (VAX collector) wrote:
They were used practically everywhere *except* in IBM/Intel/Microsoft PCs.
They're certainly not unique to DEC. IBM/Microsoft seemed to want to
standardise (not unreasonable!) and picked a particular format/size (with
minor variations).
The reason the manual says "Use only formatted RX50 diskettes" is that
formatting the 10 sectors/track on an RX50 is rather critical, and most DEC
machines to which those drives were connected, weren't supplied with
formatting software. Rainbows were, though (I think), and I regularly
format RX50s on other machines.
Pete, since the term QD or Quad Density dates back to at least the North
Star Horizon, I would submit that it was not people who didn't
understand but rather who chose to ignore the real meaning and to use
the term as it was descriptive of the expanded disk capacity.
- don
On Tue, 12 Oct 1999 allisonp(a)world.std.com
wrote:
> 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?
The number of tracks has nothing whatsoever to do with the density! RX50
is SSDD, it just happens to have 10 sectors of 512 bytes per track, and 80
tracks. Your "??? 720K" is DSDD. Yes, some people did call this QD, but
it isn't a different density at all -- the misnomer comes from people who
don't understand what the words mean. Your numbers for 180K, 360K, etc, assume a particular number and size of sectors, which
need not be the case
(ie you can use the same drive and media to make a disk of different
capacity).
Also, there's nothing about (most) drives that makes them inherently single
density or double density; that is just a question of how you interleave
clock and data pulses, and how fast you send them down the Write Data line
to the drive.
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)
Not so, the head is exactly the right width and layout for any 96 tpi DD
(or SD, come to that) media. You just have to make sure it's set to the
correct write current.
--
Pete Peter Turnbull
Dept. of Computer Science
University of York