9 Feb
2002
9 Feb
'02
5:42 a.m.
On Feb 8, 8:31, Bill Gunshannon wrote:
RX50's came pre-formatted from DEC. There was
never a way to
format them on PDP's or VAX as far as I knew. I do think it is
possible to create them using PUTR and an old PC with a proper
floppy controller and a 1.2M floppy drive configured the right
way.
You can format them on a Rainbow, but not an -11 or VAX.
My understanding is they are 80 track, 96 tpi format
but spin
at the slow spead of normal 5.25 disks and not the higher speed
used by IBM HD disks.
Very similar low-level format to IBM floppies, except that, as Bill says,
they're 80-track. The spec is 80-track, 96 tpi, single-side, double
density (not HD), 10 sectors per track, 512 bytes/sector. DEC squeeze the
extra sector in by shortening some of the gaps; even so the timing is a
little tight and the drive speed has to be better-than-averagely accurate.
It doesn't matter whether you write them at 300 rpm or 360, so long as the
controller adjusts its data rate accordingly (250kbps or 300kbps). Which
is what a PC does (uses 250kbps for 300rpm and 300kbps for 360 rpm).
However, many HD-capable drives use pin 2 on the interface not only to
change the speed but change the write current. Some such drives have
jumpers to set the correct values.
As a curious note, I actually had (and may still have
in the
attic somewhere) a real shugart 80 track 5.25 drive that would
have been the equivalent of an RX50, so it was not only DEC who
used that format. I had them on a TRS-80 and NewDOS-80 and
DOSPlus had no problems formatting and using the drive. This
was long before my first PDP, but I now wonder if they would
have been able to read and write (and maybe even format!) RX50's.
If the controller it was attached to can write MFM (double-density), then
it would work. Drives of that type were very common before PCs took over.
In fact you can fudge one to look like half of an RX50 (a real RX50 plays
funny tricks with the SideSelect and Track00 signals, and some DEC
controllers use that to recognise an RX50).
--
Pete Peter Turnbull
Network Manager
University of York