My student, Zach, has been working to debug why our bottom tape unit has been misbehaving. We are fairly certain that the issue is a short in the interface cable between the top and bottom units, because the problem appears on whatever unit is on the end of the daisy chain. Stay tuned. But in the process of monkeying with it, there was a period of time where they both worked just fine! #dec #pdp12 #pdp #retrocomputing #vintagecomputing #umdpdp12
Hi all, we did our annual PDP-12 demo in Dr. Ted Pedersen's architecture class on Tuesday, and it went really well.
In cleaning up / reorganizing after showing off our artifacts, I realized that we have something that I haven't seen on @bitsavers, but I maybe just didn't know where to look. It's a big poster of PDP-12 instructions -- it's kind of like the pocket reference in poster format. It is about 9.5x30 inches (24x76 cm). I scanned it in two pieces on the office machine and stitched it together with GIMP. I'll try to make a PDF version with OCR text. @bitsavers #vintagecomputing #retrocomputing #pdp12 #pdp #dec #umdpdp12
Today was PDP-12 demo day! #vintagecomputing #retrocomputing #pdp #pdp12 #umdpdp12
Our PDP-12 (#435) is able to read tapes (but not yet write them). This OS/8 tape is close to 50 years old and still reads well. Here we use the TYPE command to print a long listing stored on multiple tape blocks. LINC and DECtape was able to be used as random access storage (like a disk). The block numbers were written forwards and backwards on the tape so that they could be read regardless of the motor's direction!
In this video, we have a tape mounted on the top drive and have already booted. Zach requests to print the file to the (virtual) teletype, and the blocks of the file are read in sequence.
Today, Zach and I got Vince Slyngstad's PDP MM8/I memory expansion installed in our PDP-12! No magic smoke got out, the computer booted, and appears (from console and diagnostic checks) to have 32kW of memory! The PDP-12 only had room for 8 kW inside, but could connect to an external box that would include up to 24kW of additional core. Vince's expansion plugs into the five flip chip slots that would normally lead to the external unit. All memory hardware is on those five cards, with a six card providing an electrical connection. More soon! #umdpdp12 #pdp12 #pdp #dec #RetroComputing #VintageComputing
A video from the same session: #umdpdp12 #pdp #pdp12 #dec #RetroComputing #VintageComputing
PDP-12 #435 playing Spacewar! for the first time in over two years thanks to some debugging by us and our much more experienced friends on the VCF forums.
First, we noticed that minicom was inserting CRs in front of LFs when sending paper tapes, and second, someone pointed out that it looked like our 2nd 4K core was not inserted correctly (two cables were backwards).
The machine booted up like a champ, and April and Zach got their first chance to play the original deathmatch game. 
Well, our eagle-eyed and experienced friends on the VCF forums noticed something that seemed a little weird about our PDP-12... the W025 cards for Field 1 were not crossed, but were parallel like the ones for Field 0. (Seems logical, right?)
Looking at old photos showed that Field 1 used to be crossed, just like some other PDP-12s we know about.
Zach and I swapped the cards back today and...
We scoped the '12, got some useful information, and did not let any magic smoke out! https://forum.vcfed.org/index.php?threads/pdp-12-435-at-the-university-of-minnesota-duluth.1241469/post-1388752 #umdpdp12 #pdp #pdp12 #dec #retrocomputing #vintagecomputing
@davefischer @selzero Oh yes, I am extremely into this particular document! #PDP12 @tastytronic
PDP-12 demo went great! #pdp12 #pdp #vintagecomputing #retrocomputing #umdpdp12
Giving a presentation on the PDP-12 tomorrow, so Kyle and I did a little comparison of the PDP-12 and the Google Pixel 8 Pro:
- Of course, the PDP-12 is 12-bit (0-4096) while the Pixel 8 Pro is 64-bit (0-1.84x10^19)
- PDP-12 instructions vary, but are commonly 1.6usec each. The Pixel 8 Pro has 9 cores of varying speeds, but we estimate that it is around 1,300-1,800 times faster
- The Pixel 8 Pro has a million times more RAM than the PDP-12 (8GB vs. 8KB)
- If crushed into a powder, approximately 7,000 Pixel 8 Pros could fit into the space occupied by the PDP-12 (a Pixel 8 Pro occupies approximately 1/7000th the volume of the PDP-12)
- A Pixel 8 Pro costs about $1,000, while our PDP-12 would have cost approximately $400,900 in 2024 dollars! (Conversely, a Pixel 8 Pro would have cost about $135 in 1972 dollars!) We could have bought almost 3,000 Pixel 8 Pros for the price of the PDP-12!
- Millions of Pixel phones have been sold -- only about ~725 PDP-12s were sold. The PDP-8, a *wildly successful* minicomputer sold about 50k units.
#pdp12 #pdp #dec #retrocomputing #vintagecomputing #umdpdp12
So my old friend @spacehobo wrote an implementation of Hellorld! for the PDP-12, and getting it to run was quite an adventure. How old of a friend? What's Hellorld!? How quite of an adventure was it it? Watch and learn -- you won't regret it.
(Nick also did a "takeover" of our channel and produced this video, so it is well above our standard sub-standard quality!)
https://youtu.be/zcP_Dfgvuo8 ← Here is the video I did with @tastytronic explaining the `HELLORLD!` code, and documenting the entire debugging saga—complete with actual photos of my printouts at the pub, and videos of blinking console lights!
I've been editing a video about the international debugging effort that got "HELLORLD!" running on the #pdp12, and learning #kdenlive in the process. Part of that story uncovered a bug in the emulator.
https://bugs.launchpad.net/bugs/2043261 ← Of course I also uncovered a startlingly obvious bug in the #ubuntu packaging for KDEnlive. Seems that's been a theme for this project.
This program is going to be a great basis for a video about how the PDP-12 draws characters on the scope... in short, characters are 6 dots high by 4 dots wide; there are many patterns of 6x2 dots, and letters are constructed by building each character from left and right halves. You can kind of see this in the way that the H has a gap in the middle of it. When I use the "auto single-step" mode on the '12 and slow it down, you can see the characters being written one half at a time.
@spacehobo thank you so much for writing this code, and giving us something fun to run on the '12 and a new thing to describe about how the machine works!
@spacehobo So, I punched your HELLORLD! code you updated according to the actual behavior of the '12 (and now the emulation), and it works! I made some videos that I'm editing down, so stay tuned...!
