Liam on Linux

For a couple of weeks, since the 50th anniversary of Apollo 11 taking off, I've been riveted by "Curious Marc" Verdiell's Youtube channel. This isn't the first time -- his vlog of restoring a Xerox Alto was fascinating. But this project is even more historically significant: to get an original Apollo Guidance Computer running for the first time in about 45 years.

The AGC was all kinds of "first": the first computer made from integrated circuits; the first portable computer; the first computer to fly; the first computer on which humans landed on the moon.

Nonetheless I'm surprised to see the vlog even made the The Wall Street Journal.

If you don't know anything about the AGC, here's a f

antastic, very dense 1hr talk about it works.



Here's the Youtube playlist of all the restoration process.

And here's a link to the story of Margaret Hamilton, the team lead on the project of programming the AGC. You might recognise the rather famous photo of her standing next to a printout of the software, which is slightly taller than she is:


A fun detail of the software development process: not only was the machine extremely resource-constrained, and human lives depended on it -- so, no pressure then (!) -- but you must also consider the storage medium: core rope.

Core rope memory is not the same as core store. Core store uses tiny ferrite rings arranged on the intersections of very fine wires. By putting a current through both wires, the magnetic alignment of the core at their crossing-point could be read. But read destructively -- the act of reading it, erased it. Conversely, if the computer was off, the cores held their data indefinitely. People restoring 50 and 60 year old computers today can read what was in their core-store the last time they were turned off!

But core rope is different. It still uses cores, but big ones. Long wires thread in and out of cores, and the position of the wires encodes the data. So it's non-volatile: it's a kind of early ROM. You can never change the data. Ever. What was woven in when it was made is there forever. The phenomenally labour-intensive act of making it encodes the software: so weaving it was an extremely skilled task, given to experts... factories full of little old ladies, basically. This is software that is hand-knitted into the hardware. So after it's made, you can't change a single bit. The entire, multi-thousand-component hand-made rope must be re-woven.

This is CuriousMarc's playlist of the Xerox Alto restoration. The Alto was also a hugely signficant computer: the first GUI personal workstation, the machine on which the modern GUI was invented, the machine on which the pioneering object-oriented Smalltalk language was developed, and the first machine with Ethernet which more or less invented the idea of the Local Area Network. Some of original team came to admire the restoration process and help out -- and several of them are now dead.

The Alto is the machine that Steve Jobs & his team saw that led them to built the Lisa and then the Mac. They saw 3 things -- object-oriented programming, local-area networking & the GUI. Jobs himself said he fixated on the GUI and missed the (arguably, long-term) more important bits.


This really is the last possible time to restore some of this stuff — while at least some of the creators are still alive.