20 Dec
2025
20 Dec
'25
6:29 a.m.
On Fri, Dec 19, 2025 at 12:25 AM Nadav Eiron via cctalk
<cctalk(a)classiccmp.org> wrote:
I have such a drive connected to an 11/45. It's
branded as Plessey. The
drives are double density RK05 compatible (i.e., it's like an RK05F + a
"removable RK05F" with a specially marked removable pack that looks
physically like an RK05 pack) and present as 4 RK05 drives to the
controller - two on the fixed platter and two on the removable one. Haven't
had the time to try and get them to work yet, but such a device does exist.
Sounds like PM-DD/8 drives.
Connor gave me a set of four 33xx/34xx Plessey drives this year along
with a Formatter box and some cables that happen to have DEC backplane
ends but they 100% need to be deep-cleaned (gloves and respirator ;-)
before anything. I've looked at some of the docs on Bitsaves and they
appear to spin faster than DEC RK05s (2400 RPM vs 1500 RPM) and have a
similar but extended interface (mostly extra address bits) for
capacities several times that of an RK05. IIRC there are models in
this series with anywhere from just the removable platter to a
removable platter plus up to 3 fixed platters.
It does seem that the disks spin too fast to connect up to an
unmodified DEC controller even if one ignores the extra address bits
and treats it like an RK05-F. I have not investigated what's in the
Formatter enclosure except to see a large number of 14 and 16-pin DIP
ICs.
The drives appear to have an electrically similar termination scheme
as RK05 drives, but not mechanically the same and with a few more
signals (for the extra address and status/error bits).
I also got a tub of packs with the drives. Presuming they are safe to
mount, they could be interesting to image. Dates on the labels are
mostly 1980-81
-ethan