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Comment by etaioinshrdlu | Hacker News Reader

"Before microchips existed, computers were built with mechanical relays." Should probably say something about vacuum tubes as well!

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And discrete transistors. Now that my curiosity is piqued, I found this nice timeline:

https://www.computerhistory.org/timeline/computers/

It looks like transistorized computers were dominant at the point when integrated circuits were introduced.

And before that with gears! (With limited success.)

Indeed, my dad was a research scientist at a large chemical company, and every scientist had a Friden mechanical calculator, which was capable of multiplying and dividing. But it was not a programmable computer.

When the HP 35 came out, it was cheaper than the annual maintenance contract for the Friden. They bought one, and passed it around to try out for a week, then all of the Fridens went into the dumpster. Of course he brought one home, and we got to play with it.

Ha ha, the rich kids when I was in high school Physics had these calculators. It was the first I had seen them. At over $100 (as I recall) they were completely out of reach for me and half the class.

(Ands they had to either have an extra set of batteries handy or access to an outlet to plug in the cord since the possibility of the batteries dying during a test was a real likelihood.)

I like how the 1937 "Model K" adder is literally on a breadboard.

(are those knife switches in the upper right?)

U-type flat spring, see fig 2, precursor to transistor

https://www.calling315.com/relay-logic

The user facing switches are 'A' & 'B'

Interesting: the entry for the Apollo Guidance Computer (AGC) indicates it used integrated circuits—I had remembered hearing it used RTL (resistor-transistor logic).

It turns out both are true [1]. The "integrated circuits" were sort of "flat-packs" of RTL circuits. I had forgotten that early IC's were not quite what we envision today. Regardless I suppose ICs were RTL before they were TTL (before they were CMOS, etc.).

[1] https://en.wikipedia.org/wiki/Apollo_Guidance_Computer#Logic...

In particular, the IBM 1401 (two of them actually) that you can see demonstrated at the Computer History Museum in Mountain View are transistor-based and were very successful computers.

https://computerhistory.org/exhibits/ibm1401/

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