So what is a 32-bit CPU?

[tggzzz]

And then there's the Elliott 803, an influential machine. Tony Hoare (Quicksort, NULL, semaphores, CSP, Turing Award)) developed an influential Algol-60 compiler for it. The Elliott 803 was the computer used in the ISI-609, the world's first process or industrial control system, wherein the 803 was a data logger. It was used for this purpose at the US's first dual-purpose nuclear reactor, the N-Reactor.

39 bit word, 39-bit registers, 18/39-bit instructions, 13-bit addresses, 1-bit data path. Categorise that!

13 bit, but it came very very close to being 39 bit :-)

Although the accumulator (the only register except another to put the top half of a double-precision result) was 39 bits, that doesn't make it a 39 bit machine, just as the 80386 or 68020 having some 80 bit registers didn't make them 80 bit computers. And neither do the x86 string instructions.

How was it almost a 39 bit machine?

If the "B" bit between the two 19 bit instructions in a word was set then the new value of the 39 bit memory location pointed to by the first instruction (which is most often the same as the old value) is added to the 19 bit instruction in the second half of the word, before that instruction is decoded.  It's a simple arithmetic add, so that data word being added can alter not only the 13 bit address in the 2nd instruction (the most common use, for array indexing or simple pointer-chasing), it can also modify the opcode field. Or even overflow the address into the opcode. Ugh.

Since it has this indexed/indirect addressing ability there is no real need for a self-modifying code ability before instruction decode -- you can anyway just do that in memory. So they COULD HAVE instead used the entire 39 bit data word from memory as a base address added to the 13 bit offset in the 2nd instruction and had 39 bit addressing.

Not that anyone needed 2,748,779,069,440 bytes (2.7 TB) of memory (2,680,059,592,704 after subtracting the parity bit in each word) in the 1960s. They could probably barely afford the 40k bytes the machine actually supported.

The normal core store was 4k words; 8k was the architectural maximum. Youngsters don't comprehend why memory cost used to be specified in terms of $/bit (cf Gb/$ !)

I've long ago forgotten how the B bit word worked, event though it was integral to the first machine code program I wrote[1].

I'll probably see a working 803B tomorrow, and if Peter Onions is there I'll ask him. He is more than happy to whip out the blueprint schematics, and discuss them

[1] to convert from one 5-channel paper tape code into Elliott 5-channel paper tape code. I unwittingly (re)invented FSMs when doing it, one state for figure shift, another for number shift, and the events being the input characters

[coppice]

I'll probably see a working 803B tomorrow, and if Peter Onions is there I'll ask him. He is more than happy to whip out the blueprint schematics, and discuss them

Is this in a museum, or is some poor sucker somewhere still required to keep this thing alive for some ancient purpose? Its 48 years since I first touched an 803B, and that one belonged in a museum at the time.

[brucehoult]

I'll probably see a working 803B tomorrow, and if Peter Onions is there I'll ask him. He is more than happy to whip out the blueprint schematics, and discuss them

Is this in a museum, or is some poor sucker somewhere still required to keep this thing alive for some ancient purpose? Its 48 years since I first touched an 803B, and that one belonged in a museum at the time.

I'm not sure how much faster the 803B was Apparently the original 803 ran at about 2000 instructions per second (for the integer arithmetic instructions). A back of the envelope calculation says a 1 MHz 6502 from 1975 (only 15 years later) should be able to emulate it at about 10x the original speed!

[tggzzz]

I'll probably see a working 803B tomorrow, and if Peter Onions is there I'll ask him. He is more than happy to whip out the blueprint schematics, and discuss them

Is this in a museum, or is some poor sucker somewhere still required to keep this thing alive for some ancient purpose? Its 48 years since I first touched an 803B, and that one belonged in a museum at the time.

TNMoC, of course. In neighbouring rooms there is the world's oldest operating computer (based on dekatrons) and a couple of slide rules with 500"/12.2m scales.

Oh, and a Bombe (working) and Colossus (working) and Tunny / Heath Robinson / Enigma / ICL2900 (working), of course. Don't envy them their electricity bill, and I always make a donation when visiting.

Don't forget to ignore the Bletchley Park museum next door; it is a standard museum where the attendants have - at best - read "Cliffs Notes" about the exhibits.

[brucehoult]

TNMoC, of course. In neighbouring rooms there is the world's oldest operating computer (based on dekatrons) and a couple of slide rules with 500"/12.2m scales.

Oh, and a Bombe (working) and Colossus (working) and Tunny / Heath Robinson / Enigma / ICL2900 (working), of course. Don't envy them their electricity bill, and I always make a donation when visiting.

Don't forget to ignore the Bletchley Park museum next door; it is a standard museum where the attendants have - at best - read "Cliffs Notes" about the exhibits.

I really must visit the Old Country sometime before I can't. The closest I've been is Sweden / Denmark / Germany / Austria (well, and CDG and AMS), and I lived three years in Moscow.  My great-grandfather was a publican and butcher somewhere in the middle of Nottingham, Birmingham and Manchester before he emigrated to NZ in the 1880s.

There are one or two interesting things there, though on the whole it appears far too expensive and overcrowded to stay long. Bletchley looks handy to Silverstone, which is another thing that might attract me to the area. I've only been to races (twice) in Sochi. I'd also like to visit a certain section of A487, and that's also only about 20 miles from a certain charming village where you have to watch out for stray weather balloons.

[coppice]

TNMoC, of course.

Why do you say of course? Its quite astonishing how much ancient kit is still operating in one or two locations that just won't replace it. Its often doing a mission critical job, where the people overseeing it haven't the slightest clue what they would do if an irreplaceable component fails. Luckily for them, there are few irreplaceable parts in an 1960s computer. The parts just cost a bit. On the other side, the entertainment system just failed in my next door neighbour's 20k miles 2017 VW Polo. 150 pounds to have it diagnosed. 2500 pounds to have it replaced. Its not clear if all the functions needed in winter would still work without the entertainment system. Nothing in it is serviceable, as its apparently almost always one of the custom parts that fails, and VW don't like to provide those to 3rd party repairers. Isn't progress wonderful. The future is in recycling. Or was that cycling. Something like that.

[tggzzz]

I really must visit the Old Country sometime before I can't.

Know what you mean

If you do, there are a number of worthwhile museums, and I rather like the rarely visited neolithic sites too.

I'd also like to visit a certain section of A487, and that's also only about 20 miles from a certain charming village where you have to watch out for stray weather balloons.

Would that be near an establishment that, 10-15 years ago, had appalling inaccurate GPS accuracy? And, more recently, where pilots couldn't experience the full fun of being in an aircraft?

I frequently see stray balloons with baskets underneath them; fun once, but gliding was better