[pups] Duh - how do you format an RX50?

Pete Turnbull pete at dunnington.u-net.com
Sat Feb 9 09:42:20 AEST 2002

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

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