micropolis disk question

From: Ethan Dicks <erd_6502_at_yahoo.com>
Date: Thu Apr 10 10:46:01 2003

--- Ed <quapla_at_xs4all.nl> wrote:
> Hello all,
>
> I have picked up 2 micropolis disks, type 1325. Question is, are they
> ESDI or ST-506 type of disks? The card edge connectors are identical.

ST-506/ST412, not ESDI. The ESDI drive that looks like these is a
model 1355, IIRC. I've seen the ESDI drives in old outboard Sun
boxes.

The 1325 can be converted to DEC use (as a 73MB RD53) by adding
the infamous 0 ohm jumper at R7, then low-level formatting on
a MicroVAX 2000 (using the ROM diagnostic formatter) or a Qbus
MicroVAX with an RQDX3 and the Diagnostic tape formatter, or
even a Qbus PDP-11 w/RQDX3 and XXDP. It large enough to run
VMS 5.0 (barely) or 2.11BSD (barely) or 2.9BSD (with some room to
spare). RT-11 is a possibility, too (v5.4 and up?), but you'd have to
partition the drive into multiple "devices".

To get to the jumper, loosen the two flat-head screws at one end of the
circuit board on the bottom of the drive, tip it up (it's on a pivot),
and look for R7 on the silkscreen, somewhat near the middle of the
board. Solder in a jumper wire, reassemble and install! If these drives
came out of a PeeCee, check the unit jumpers before putting them to
use in a DEC machine.

To forestall any "warnings", you will probably find that these
drives do not have the best longevity. Many of them have lots
of hours accumulated already. They probably won't stand up to
heavy use. The bearings seem to go in the ones that I've had
fail. I don't think I've ever had a head crash.

-ethan
Received on Thu Apr 10 2003 - 10:46:01 BST