|Half Adder, with Pentodes (I think)|
I dug this out the other day ; it's great. It's full of circuit diagrams like this. No, valves are beyond me, really, but I think they operate a bit like transistor switching circuit ; this particular circuit is an single bit adder. I remember having a book about single channel radio with valves when I was about 11 (I was a deeply sad child).
The machine is entirely serial in operation, so rather than having a bank of adders it just feeds them through one after the other - you can see the carry going off the bottom and coming back on the top.
It pretty much answers all the unanswered questions, like how does the BINAC pack two instructions into a single word memory location,
More than that, it has some real BINAC code. The code shown below (well, probably) is a real BINAC program. I didn't think I'd ever actually find one. The nearest is an article "Do you want to buy a Brain ?" which is published in May 1949's "Popular Science" which has a very simple program written by Jean Bartik (a lot of these early programmers are women) to do a payroll calculation, but it's more about getting the idea across than real code. The article is really about UNIVAC, but that didn't exist in 1949, so the actual worked examples are for BINAC. There won't be much real BINAC code, you could copy memory onto an early form of magnetic tape (another first I think) but it didn't work that well, apparently.
(Note, the sequence goes ; ENIAC -> BINAC -> UNIVAC)
Anyone notice how dumb modern stuff is by comparison. This Popular Science article has valve circuit diagrams explaining how logic gates work, explains binary, mercury memory tanks and things like that.
I remember when I was a kid, there was a Ladybird Book (for non UK readers, this is a series of fiction and non fiction aimed at under 11s) called "How to make a transistor radio" and it does, with regenerative feedback, and it explains it as well, properly, like an Electronic engineer would. I still have it.
Today all people do is Powerpoints ......
I sometimes think my early days with an SC/MP Introkit - 256 bytes of RAM and a calculator hex keypad - were actually a huge advantage. Perhaps writing BINAC code, or something like PDP/8 (I used one at University, briefly) should be compulsory ?