RPC-4000 magnetic drum computer -- software? - Page 1
Forum section: electronics / general

author: ebastler
author_rank: Super Contributor
timestamp: September 19, 2024, 10:24:48 am
content: Several years ago I built a little replica of a 1960 computer, the RPC-4000. A rather exotic machine from today's perspective, it was one of the last computers which used a magnetic drum as their main memory. No RAM as in "random access memory" -- the computer had to wait until the next expected instruction or data word arrived at the read heads. I have a short project description here:https://www.e-basteln.de/rpc4000I built this as part of a series of similar models, knowing full well that no preserved software was available online. I had a couple of leads to potential "offline" software, and was hoping that availability of a machine to run the software on would motivate people to do some digging. But nothing has materialized so far.So here's a long shot: Any ideas who might have software for that machine stashed away somewhere? It would most likely be on paper tape -- 6 data bits + parity, this was before ASCII... Thank you for any leads, or for checking in your basement!

author: tggzzz
author_rank: Super Contributor
timestamp: September 19, 2024, 11:00:45 am
content: For the background significance of the machine, cue "The Story of Mel"Overview:https://en.wikipedia.org/wiki/The_Story_of_MelFolklore details:http://www.catb.org/jargon/html/story-of-mel.htmlYes, I knowyouare familiar, but others probably aren't.https://www.e-basteln.de/computing/rpc4000/storyofmel/#startI've considered doing an FPGA version of the Elliott 803, but life is too short

author: ebastler
author_rank: Super Contributor
timestamp: September 19, 2024, 11:08:02 am
content: Thanks for chiming in! Right, one of the claims to fame of the RPC-4000 is that it is the computer discussed in the "Story of Mel", my favorite piece of hacking folklore. The non-random-access nature of the drum memory really invited the coders of the day to optimize the heck out of their programs -- arranging instructions and data in optimal positions on the drum to minimize wait times.Since I had already spent an embarrassing amount of time digging into the RPC-4000 design and instruction set, I also looked into the technical details behind the "Story of Mel". Was that hack as described by Ed Nather really possible on the machine? Here's more detail about this than you ever wanted to know:https://www.e-basteln.de/computing/rpc4000/storyofmelEDIT: Ah -- noticed that you edited the link. I'll leave my post here anyway. If anyone has not come across the Story of Mel, please do take a look! (At least at the original story; the technical analysis is optional.)

author: tggzzz
author_rank: Super Contributor
timestamp: September 19, 2024, 11:56:44 am
content: Quote from: ebastler on September 19, 2024, 11:08:02 amNot quite sure how I originally inserted a slightly different URL. Edits passing each other in the æther happens.Yes, the Mel Story is a good "you don't know how luck you youngsters are" anecdoteI first came across it in 1989, in alt.folklore.computers

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 20, 2024, 10:40:35 pm
content: Didn't Edward Lorenz use this computer? Maybe talk to his alma maters.https://en.wikipedia.org/wiki/Edward_Norton_Lorenz

author: ebastler
author_rank: Super Contributor
timestamp: September 21, 2024, 05:38:35 am
content: Quote from: Alex Eisenhut on September 20, 2024, 10:40:35 pmLorenz used the earlier machine, the LGP-30, for his weather simulations. (Which led him to discover the "butterfly effect" and chaos theory, when he noticed that long model calculations that were continued the next day, based on manually entered restart parameters, sometimes took an entirely different path.)Also a bit-serial computer design with magnetic drum memory, but still tube-based. Quite a bit of software is preserved for that machine, including the original Blackjack tradeshow demo which was written by Mel Kaye and features in the Story discussed above.I have actually been in touch with MIT about this: When they ran a Lorenz memorial symposium a few years ago, they wanted to give a feel for how Lorenz had worked. Since they could not locate a working LGP-30, they used mylittle replicaconnected to a teletype to run some demo calculations. But I am not aware that Lorenz used the RPC-4000; he must have upgraded to something more modern.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 23, 2024, 12:20:32 am
content: Awesome, the panel and display looked familiar, I read Gleick's Chaos years ago. I should read it again.