Back in March of 2012 I was watching Duplicity and I noticed something odd about 28 minutes in:
In the top right corner there’s an 11×17 paper with an image on it that’s really hard to make out. I recognized it instantly. I first saw the image in question over 30 years ago when my dad brought home from work the November 1982 issue of a magazine called “The DEC Professional” that had the image in it. The image is a hand drawn map of Dungeon.
For the uninitiated, Zork is Infocom’s classic text adventure game. They renamed it to Dungeon at some point, but changed the name back to Zork when they started selling it. My dad had a copy of the Fortran translated version of Dungeon on his PDP-11. My friends and I called “Dungeo” since the filesystem only allowed 7 letters in the name—I didn’t get that it was actually called Dungeon until I was much older [Ed. 2022-07-08: I recently created dungeo.org in homage to the name, check it out!]. So when he brought the magazine home, it was specifically because of the included map and because he knew I loved the game.
I must have stared at this map for days, cumulatively. My cousin traced it, enlarged it and hung it on his wall (and recently recreated and enhanced it). I currently have a black and white photocopy hanging in my computer room. I always thought it was a very good map (even though it lacked the “end game”). The point is, I’ve known and loved this image forever.
But it’s also obscure! How many people had PDP-11s and played Dungeon and happened to see the map in “The DEC Professional”? And how many of them had this map make an impact on their lives? To me it seems like that can’t be a very large number…
And so it was crazy to me that I’d happen to see that map that had made such an impact on me be in a movie that came out 27 years after the map’s publishing in an obscure computer magazine. Who was the set decorator that grabbed the map? Did he know what it was? Was it someone else’s and he just thought it looked cool? If so, whose was it? IMDB says the set decorator in Duplicity was George DeTitta Jr. But what it doesn’t say is, “why?”
This is basically the 1974 version of a DIMM. It measures 16″ by 11.5″ and holds 16 kilobytes. It’s technically 18 bits wide but only 16 were used in the PDP-11. The raised part in the middle is where the cores are actually stored. Each bit is a little ring with 3 wires running through the middle. By running current through the wires you could magnetize or demagnetize each ring. One interesting tidbit is that reading is destructive! When you read a bit you are actually demagnetizing the ring and the memory controller had to then do a write cycle to restore the bit. You can’t see the rings in the picture (I’m guessing they kept them covered because they were fragile), but you can see some nice pictures and a more in-depth explanation at the Wikipedia page.
The cool thing about the module is that everything is discrete. There’s not a custom chip in sight. Along the bottom and right edges of the board you can see the row and column drivers. On the right you can see 18 instances of the sense amplifiers and inhibit drivers (1 for each bit in the word).
Here’s some pictures of the computer it came out of:
That is a PDP-11/05 that my dad built from scratch. That top part is the main computer (the processor is not a microprocessor, instead it’s made from discrete parts). It was all wire-wrapped by hand. Here’s the back:
I can’t even imagine having the patience to do that! All the colors of wire mean different things, too (they’re grouped by logical parts of the computer–data paths, control paths, clocks, etc). The slots below the board are for expansions cards–electrically they are Unibus but their physical form factor is custom to his computer. Here’s the hard disk controller card:
This disk controller could support 2 10MB hard disks. The computer also has a floppy controller (for 8″ floppy drives) and a RS/232 controller card (3 ports).
It’s funny that I grew up with this computer (and later a PDP-11/34 with 2 rack of equipment) but never cared about what kind of thought and work must have gone into it… I was always way more interested in my pirate Apple ][+ clone that I put together from a kit in second grade (if you’ve never used an Apple ][ before, try this emulator I recently wrote in HTML5). But now my dad decided to get the PDP back up and running so he’s been showing me all the little parts and I think I’m old enough now to appreciate it.
The interesting thing for me about all this old technology was how amazingly straight forward 90% of it is. For instance, the front panel has a keyboard that shifts 3 bits at a time into a shift register and then lets you generate bus cycles (all driven by state machines in hardware). This was instead of the DEC’s computers which makes you enter binary with 16 individual switches–it’s a nice, simple addition that makes it way more pleasant to work with than the standard PDP-11 and it’s totally understandable.
Fine so far. But I noticed that on both wikipedia and the NOAA site they say that the sound is sped up 16x. So I wanted to hear what it sounded like in realtime. I slowed it down with audacity (which turned out to harder than it should have been), and reveled in the deep bass.
Today I saw another link on Reddit to someone who had done the same thing. I checked out their real-time sound and it didn’t sound at all like mine. I realized that they used a pitch shifting style effect to slow the sound down without changing its pitch. When you slow something down that much it introduces a lot of artifacts, which are clearly audible in their file. In order to attempt to fix that they have another version that’s been run through some sort of noise reduction filter which causes even more bloopy (so to speak) artifacts.
If you check the original spectrogram on the NOAA’s site it looks like this:
Notice that the top frequency there is 50Hz. That is low. We’re talking deep bass. So I’m pretty sure the correct way to slow it down is to actually just slow it down and let the frequency drop all the way down.
I was rearranging my bookcase and happened across a 1976 Readers Digest (when I moved into my Grandma’s old house I left all her books there). I flipped through and read the jokes (they had a “don’t step in the hoya” joke which I had also just seen on reddit in the last couple weeks) but what really caught my eye were the ads. Most had very stilted layout without a lot of font choice or flair. Graphic design must have been annoying back before computers.
Then I saw this ad and just had to laugh!
Apparently our vision of what a small car is has changed a lot over the past 40 years. Plus that guy’s suit is just awesome.
My sister accidentally left her phone in a McDonald’s in LA the other weekend. When she went back, someone had taken it and not given it to the lost and found. When she called her number they would answer and then immediately hang up. So she called Verizon and reported it as stolen. Soon after a woman name Sheila called my mom and said she found my sister’s phone out side a Food For Less store in Santa Clarita. My mom asked if she would mind mailing the phone back down to us so that she could avoid making a 140 mile round trip to pick it up. Sheila balked (it was way too much trouble for her) and so my mom offered to mail a self addressed, stamped shipping envelope to her. She grudgingly decided that would be OK.
Today they got the phone in the mail (yay!) along with a folded up note. Here’s what it said: