Al K. wrote:
>there are two versions. the 1981 8560 uses microp 1200, later ones have xebec
>1410 and are sasi
>070-3899-00_8560_MSDU_Installation_Guide_Nov81.pdf
>070-4759-00_8560_8561_8562_Service_Mar84.pdf
If the 8560 in question uses the 8" hard disk drive from Micropolis, then
Bitsavers also has the documentation for the drive, which is the same document
I used years ago to build the hardware interface and write the code to talk to
the drive:
http://bitsavers.org/pdf/micropolis/100292_Specification_1220_Series_Rigid_Disk_Drive_Subsystems_Oct79.pdf
There is a jumper block on the 1220's controller board that configures the
sector size. This wasn't documented in the above documentation. I needed 512
byte sectors, and the drive didn't seem to be responding that way (it turned
out it was configured for 1K-byte sector size), and I had to use the schematics
for the drive to figure out how to wire up a jumper block that would
reconfigure it for 512 byte sectors. And yes, I could have written the driver
to deal with this, but I didn't have a lot of memory available for the sector
buffer, so I decided to try to figure out how to reset the sector size to 512
bytes. The problem is, I can't find the schematic anywhere for the Micropolis
1220 controller board. That schematic holds the key to wiring the jumper block
for the sector size.The original jumper block was encapsulated in epoxy.
I don't remember what sector size TNIX (the Unix kernel that ran on the 8560's
CPU (which was a PDP 11/23)), but if the drive is working well enough, you
should be able to figure out the sector size being used. If you found another
drive that had the controller, you could just remove the controller board, and
daisy chain the drive in, and it'd end up using whatever sector size the
controller board on the internal drive is configured for.
For some time I had an 8560 that I tinkered with for a while. It was one with
the Micropolis 8" drive. I bought it at the Tek Country store for pretty
cheap...power supply was kind of sick, so I fixed it, and got it running.
Fortunately, no one changed the root password from the default, so I could
login to it. I found TNIX to be painfully slow, as I was used to using BSD on
a VAX. Someone at Tek had done a build of RT-11 that ran on the box, and I
played around with that for a while...it was a lot faster than TNIX, but not
really multi-user like TNIX. After a while I got bored with it and ended up
giving the system to someone that I found that was really interested in it.
When some of those Micropolis 8" drives showed up for pretty cheap at the
Country Store, that's what led me to buy a few of them and hook 'em up to my
Board Bucket system, which hosted a local computer bulletin board system (Bit
Bucket Bulletin Board, Portland, OR). The drives were power hungry, made a
lot of heat, and were also rather noisy. I eventually replaced them with a
home-built SASI interface, a Xebec 1410 SASI to ST-506 converter board, and a
couple of 40MB 5 1/4" full-height Micropolis disk drives. They were a lot
quieter, used a lot less power, and were faster. I think that the old
Micropolis 1220/1200 drives were tossed out in a move somewhere along the line,
which I regret.
It would not be terribly difficult to build a piece of hardware that emulated
the Micropolis drive, using some little computer (Arduino, etc.) or even a PC
through a parallel port perhaps.Using a SSD or even a USB thumb drive for
storage in it would provide lots of disk space for multiple disk images which
could be connected up to the 8560 host to appear as individual drives, and, if
the code was written reasonably well, the data transfer rate could be decent
(the drive isn't terribly fast).
If the 8560 you have is one with the Xebec SASI to ST-506 board in it and a 5
1/4" hard disk drive, then I think that the expansion port is actually SASI.
That said, though, you likely won't find many if any SCSI drives that will
work with that interface. I think, though, that the Xebec S1410 could control
two ST-506 drives. Cables might be able to be cobbled up to add a second drive
to the system (probably wouldn't fit in the chassis) off of the 1410.
However, finding good working ST-506 drives today is quite a challenge.
And..you'd have to find a drive that was compatible with the system in terms of
geometry.
It would be really good, though, if somehow the original disk in your system
could be imaged at the byte level. I doubt that there are very many of the
8560's around that still run.
-Rick
