Episode 165 - LSI-11

Imagine a secret number that could be used to bring your computer to a screeching halt. In 1977 Gerry Wheeler discovered an interesting feature of Motorola's new 6800 microprocessor. There was a secret instruction that, if read, would cause the processor to stop working. He called this magic number Halt and Catch Fire, or HCF, and wrote a neat article about the operation. This was the first time the public would learn about the secret powers of HCF, but this isn't actually the beginning of the story. When it comes to HCF things are more complicated than that... but only a little bit!

Have you ever had a computer do something you can't explain? Have you ever thought a machine had a mind of its own? In 1971 Met Life was faced with this exact conundrum. Their tape drives, for some reason, were throwing tape all over the floor every night. Systems were checked and no flaws were found, but every morning an operator would walk in on an absolute mess. What could make a healthy machine spit up it's precious tape?  

My trilogy on the PDP-11 concludes with a look at the far flung places this computer can take us. In this episode we look at some issues with claims of the PDP-11's linage, smuggling, Hungarian-made microcode, and much more. Along the way we answer the question: if the PDP-11 was such a good design then where was it during the home computing boom of the 80s?  

This episode we continue my series on the PDP-11 by examining how DEC adapted to the advent of the microprocessor. Along the way we will see how the PDP-11 inspired new generations of computers, and the surprising connection to early digital hobbyists.  

Last weekend I had the chance to talk about the LGP-30 and my emulation project at VCF West in Mountain View, CA. The showrunners will be posting a full video later, but that takes a while to go live. In the meantime, here's the audio I siphoned off the sound board and my slide deck. View my slides here: https://drive.google.com/file/d/1E9-B3EzxudFWX0yJMevbbIkD2qRbBKWi/view?usp=sharing View the emulator at: https://lgp30.org

The DEC PDP-11 is one of the most influential minicomputers of all time. Some would even call it the most influential computer of all time. But where exactly did it come from? How was it designed? This episode is the start of a 3 part series that will look at how the PDP-11 was created, adapted to changes, and the strange places it ended up.  

In 1949 CSIRAC sprung to life in a lab in Sydney, Australia. It was a very early stored program computer. All machines of the era were unique. But CSIRAC, well, it was very unique indeed. Selected Sources:  https://cis.unimelb.edu.au/about/csirac/music/reconstruction - The Music of CSIRAC https://sci-hub.se/10.1109/MAHC.1984.10014 - Pearcy and Beard on CSIRAC

The first batch of digital computers emerge directly following WWII. The hallmark of this generation is uniqueness: no two computers are the same. However, there is a machine that bucks that trend. The IAS Machine, built in Princeton in the late 1940s, served as the inspiration for at least a dozen later computers. But how similar were these Princeton-class computers? What exactly was so special about the IAS Machine? And how does good 'ol Johnny von Neumann get tied up in all of this? The Eastern Boarder map fundraiser Selected Sources: Bigelow Oral History - https://www.si.edu/media/NMAH/NMAH-AC0196_bige710120.pdf Prelin IAS Machine Report - https://www.ias.edu/sites/default/files/library/Prelim_Disc_Logical_Design.pdf  

Lunar Lander is one of the best loves video games of all time. The game was created in 1969 as an homage to the recent Apollo 11. From there it would only spread. Just about anything that can print text has it's own version of Lunar Lander. The early history of this game is mixed up with something weird: two nearly identical programming languages. Today we will be using the history of Lunar Lander as a good excuse to look at an obscure tongue called FOCAL. This language is so close to BASIC that direct line-by-line translation is possible. But are the two connected?

In 1982 Intel released the iAPX 286. It's was the first heir to the smash-hit 8086. But the 286 was developed before the IBM PC put an Intel chip on every desk. It's design isn't influence by the PC. Rather, it reaches further into the past. Today we are looking at the strange melding of old technology, new ideas, and compatibility that lead to the 286.