Your quote "to get into the head of those original engineers" is a great
sentiment on what the hobby is about.
I recall reading about early "steam tractors" - almost trains, before there
were any tracks. Monstrous things, I can't recall if they were before
steam ship engines - but exploding broilers was a problem (which I view as
being akin to "exploding batteries" that we might occasionally deal with
today- it happens now and then, as we still haven't perfected the tech {or
at least, hadn't 10 years ago}).
I'm reading more about those electric powered flying vehicles - with some
becoming available around $120K? I think the Joby eVTOL recently did a
first public flight between two airports. I've been flying one in MS
simulator, neat to see that they might become a reality. The main
naysayers of electric-anything vehicles tend to point to cold weather
(northern winter) environments.
Anyhow, those "personal minicomputers" from 1968-1969 are neat. It's a
whole generation of computing that (IMO) is kind of forgotten about - but
then again, they cost as much as a house then, so generally only business
owners (like supermarket owners) could afford them. I suspect Gomez
Addams had a few in their basement :) I've seen some Data General's of
that era restored. I'm still trying to see if there are any functional
DDP-116 or SEL810B around - but you're right, flip-switch programming is
kind of a drag and working teletypes are hard to find these days.
You mentioned having your own RAM card, like custom built? Someone
recently made an SRAM based replacement RWS for the IBM 5110. Neat stuff,
I never yet had the patience (or equipment) for that kind of detailed
signal analysis to reverse engineer something like that.
-Steve
(voidstar / Domesticating the Computer)
On Tue, Aug 26, 2025 at 11:26 AM Paul Koning via cctalk <
cctalk(a)classiccmp.org> wrote:
On Aug 26, 2025, at 10:51 AM, Martin Eberhard via
cctalk <
cctalk(a)classiccmp.org> wrote:
Interesting for Tesla’s early history, but skip
to 49:00 for a nice rack
he is putting together with an 11/20.
https://youtu.be/88KHfX_kPIY
He also appears to be on the cctalk list.
:-) Yes, I'm on this list. I was surprised to see Kim Java show that
snippit of my PDP11/20 restoration project. I wasn't even aware that the
camera was rolling at that point!
So far, the CPU and the extended arithmetic element seem to be working
great. I've got my own SRAM board
<
https://deramp.com/downloads/mfe_archive/005-Documentation%20and%20Code%20b…
in it. The RX211 is also working great, as is the DL11. I'm in the
process
of restoring the RK11 disk subsystem (RK03 Diablo
drives, external
controller). I can now read, write, and format on one of the drives. The
other has lots of work to be done. I need to tear both drives apart
enough
to replace the rotted foam seals for the
air-blower interface, and the
rubber strip on the front door. I am also considering cleaning and
re-lubricating the bearings on the positioner assembly. as they feel a
little crunchy. Amazingly, I just bought new air filters for the Diablo
drives!
Nice!
How do you load software into it? There's always the toggle switches if
you have enough patience. Or do you just update the ROM?
For that machine, with a full load of memory, you have a bunch of OS
options. RT-11/SJ or /FB, DOS-11, RSTS-11. That last option would be
amusing: a machine quite similar to yours, with the addition of DECtape and
another 15 DL11 interfaces, is what my alma mater used for the college
timesharing system in 1973-1974.
paul