[philwelch]

This is the first I’ve heard of Colossus influencing the ENIAC. I was under the impression that Colossus was so secret that ENIAC was designed independently and (falsely) touted as the first tube computer prior to Colossus’ existence being declassified. I’m not sure if I’m misremembering that though.

[Animats]

The ENIAC seems to be the first general purpose electronic digital computer. It wasn't stored program, though - no good memory devices. Plugboards and lots of rotary switches. Took hours to load a new program. Unrelated to Colossus.

The first machine to have it all was the Manchester Baby.[1] Now this really was sort of a descendant of Colossus, with some of the same people involved. It was mostly a test rig for the Williams Tube memory device.

Once there was something that could do the job of RAM, things took off quickly. Within two years there were quite a number of stored program electronic digital computer projects. Electronic arithmetic worked fine, but everybody had been stuck on the memory problem.

[1] https://en.wikipedia.org/wiki/Manchester_Baby

[adrian_b]

Several earlier electro-mechanical computers were closer to a modern computer than ENIAC from the point of view of program storage, as they had a clearly defined instruction set and the programs were stored on punched tape (taken from teletype machines).

With ENIAC, reconfiguring the computer for solving a new problem was done essentially in the same way as for an analog computer (or nowadays for an FPGA), by rewiring the connections between the arithmetic units, the storage registers and the control sequencers, so that ENIAC will solve the new problem when powered on.

The resemblance of ENIAC to an analog computer is not an accident, but its architecture has been conceived as an electronic substitute of the electro-mechanical analog computers known as "differential analyzers", which had been in widespread use both before WWII and during WWII, for computing solutions of systems of differential equations, which were found in various engineering problems, including in many of military importance.

On the other hand, Harvard Mark I had been inspired by Babbage's proposal for a digital computer with stored program, hence its architecture much closer to modern digital computers.

While ENIAC had an architecture inspired by the mechanical differential analyzers, for the schematics of its electronic arithmetic and register circuits it used some information from the designers of the earlier Atanasoff-Berry Computer, which was a special-purpose electronic computer for solving systems of linear algebraic equations, and which included even the first DRAM memory (the second DRAM memory will be the British Williams CRT).

[maxbond]

Any good books to recommend on computer history?

[adrian_b]

Colossus did not influence ENIAC.

However, there is a connection between British electronics and ENIAC, which is the same, but happened in parallel, with the connection between earlier British electronics and Colossus.

During the decade before WWII, several fundamental circuits of digital electronics had been invented in UK, e.g. several kinds of electronic counters and the Schmitt trigger.

Those circuits have been invented mainly for use in experiments of nuclear physics and elementary particle physics, e.g. for counting events from radiation detectors, for which the existing mechanical counters and accumulators were too slow. The first digital electronic circuit, the Eccles-Jordan trigger, had also been invented by British physicists, but another decade earlier, at the end of WWI.

The British digital electronic circuits were a source of inspiration for the circuits used in the first (special-purpose) digital electronic computer, the Atanasoff-Berry Computer, which was built at Iowa State University immediately before WWII (the published British research papers were explicitly quoted in the ABC design documents).

In turn, the digital electronic circuits used in the Atanasoff-Berry Computer were a source of inspiration for those used in ENIAC, because a member of the Mauchly-Eckert team had visited the designers of ABC, inquiring about its components, even if later they did not credit any source of inspiration for the ENIAC design (the Mauchly-Eckert team founded a startup for making electronic computers, so they were wary of providing any information that would make their work appear as less original and not patentable and they were also extremely annoyed by the publication of the von Neumann report, which explained for everyone how to make an electronic computer, so it created very soon a great number of competitors for the company of Mauchly and Eckert).

[maxbond]

I think you're right, my mistake. I didn't find anything definitive but given they were developed around the same time by (on cursory inspection) different people and that Colossus was as secret as you say (it wasn't declassified until the 70s), it does seem unlikely. I thought that had been mentioned in a Computerphile/Numberphile video on the topic but I must be mistaken.