4 May
2007
4 May
'07
12:33 a.m.
Tony wrote:
There are 2 possible interfaces for the Micropolis
1203.
The bare drive has a 50 pin connector, which is
somewhat similar in
concept to the SMD interface. There's an 8 bit parallel data bus with
strobe lines, etc, to do things like head postiioning, and a raw data
stream.
There was a Micropolis controller board, the same
physical size as the
drive logic board, that could be scrrwed onto the
drive. I think the
host
connector on that was also 50 pin, and it has the
interface you're
describing. This controller did the conversion between the 8-bit
parallel
data to the host and the bitstream to the drive.
The Tektronix machine that started this thread used
that controller
(so
presumably it was also common on drives obtained from
Tektronix
surplus).
Yes, the drives that I got my hands on (I also had an 8560 at one point
running TNIX) all had the Micropolis "controller" board that was
positioned over the top of the "bare drive" logic board. I probably had
three or four of these things at one time, but over the years, they
either died, or I gave them away to friends who had interested once I
was able to afford another Micropolis drive, the 5 1/4" ST-506 interface
20MB drive (can't remember the model number).
The 8" Micropolis drive was also used in the Tektronix Magnolia...a very
early prototype workstation-class machine that used a bitmap display,
and was based on Smalltalk as the native operating system. Tek (to my
knowledge) never sold any of these machines, but quite a few of them
were built as prototypes, and used in various areas of Tek as
engineering workstations. The Magnolia was way ahead of its time. Had
Tek had the marketing and sales skills to sell this thing as a computer,
they could have grabbed the engineering computing workstation market
before it even really existed. This was long before Sun or PERQ. It
was more in the timeframe of the early Xerox PARC machines. In fact,
some of the software engineers that developed the working environment
for the Magnolia came from Xerox PARC.
The 5 1/4" full-height Micropolis drives were the "standard" drive in
the early Tektronix 6130 UTek machines, and I could get them at Tek cost
plus 10%, making them reasonably affordable, as Tek purchased them in
large volumes. These were interesting drives, because they had two
platters in them. One surface had pre-recorded information used by the
electronics for accurate head positioning. In the drive as it came from
the factory, only two surfaces were used for data (for a total of three
surfaces, two data, one servo). However, there was a head, and
amplifier for the remaining surface. Each surface held 10 Megabytes, so
the standard drive had a capacity of 20MB. There was a little flex
circuit board that came out of the sealed HDA that terminated on a 2x4
square pin header that plugged into a socket on the drive logic board.
On these drives, the two pins that went to the head/amplifier for the
"unused" surface were simply cut off. We found that if we carefully
desoldered the disfigured header, and soldered in a full 2x4 header, we
could format these drives as 30MB drives, and they worked just fine.
Sometimes when low-level formatting, there would be a few flaws on the
third surface, but nothing major...resulting in only a slight reduction
in capacity. I'm thinking that originally all of the drives were
manufactured as 30MB drives, and that those that had some number of
flaws in a certain surface would have that surface "disabled" by simply
cutting off its pins to the main logic board. Apparently the drive
electronics could tell which were "good" surfaces by those which had a
signal riding on them, and make it all transparent to the ST-506
interface. A cheap way to make sellable (albeit lower-capacity) drives
out of drives that failed QA testing as 30MB drives.
These drives were pretty bulletproof, too. I still have one (modified
as described above) in my Tektronix 6130, and it ran literally for
something like 8 years straight. Then, I got my hands on some Sun
machines, and the 6130 was put aside. However, about a year and a half
ago, I had occasion to run into the 6130 while unpacking stuff from a
storage unit, and I brought it home, hooked it up to a trusty Heathkit
H19 terminal, and powered it up. It booted up right away. Not even a
fsck required. I even remembered the root password! Did a full "dd" of
the disk to /dev/null, and no read errors at all. I think I still have
a couple of these drives stored away. I should drag them out and see if
they still spin up. Probably could get them to talk to an old Adaptec
ACB-4000 SCSI to ST-506 converter, and hook 'em up to a PeeCee with an
Adaptec Single-Ended SCSI controller (I have a slew of ISA and PCI-bus
HBAs) to see if they still work. I'd bet dimes to donuts that they will
work just as good today as they did in the mid-'80's.
-Rick