My understanding is that diodes (and other electronic components like vacuum tubes) started to be used in this line of Harvard machines, only with the Mark III computer.

Does anyone have some information about the usage of this kind of component in the Mark I or II?

  • What do you have in mind specifically when you say "diodes"? Be aware that the term "diode" originally referred to a vacuum tube rectifier, not a solid-state device…
    – user461
    Sep 8, 2018 at 9:04
  • 1
    I mean any kind of diode. I'm familiar with diode vacuum tubes. I think the Mark I and II were not using them at all, but I'm just not sure.
    – nbloqs
    Sep 8, 2018 at 21:51

1 Answer 1


Compiling some information from the internet shows that the Harvard Mark I and Mark II were purely electromechanical machines. The main reason for this was actually financial: it was cheaper to build these conceptual machines using relays Howard Aiken

The computer introducing the control store concept using a diode matrix is the IBM Whirlwind in 1947.

The Harvard Mark III was completed in 1949, but I can't seem to find when work on it started.


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