The smallest pre-IC computer is probably an aerospace computer. These computers are very interesting, but almost totally neglected. For instance, in 1960 Atlas ICBMs (nuclear missiles) were guided by a computer that was a two foot cube and weighed 240 pounds. Side note: PROM memories were invented for this computer, so missiles could be aimed at different targets in the field.
In 1962, Arma created the first microcomputer, or at least the first computer with that name. The Arma Micro Computer was a general-purpose aerospace computer built from transistors and transfluxors (two-hole core memory with a cool name). The computer was a tiny 0.4 cubic feet and 20 pounds. It was a 22-bit machine; while we now think word sizes must be a power of 2, back then people used whatever word size gave them the accuracy they needed.
The original Atlas guidance computer was ground-based.[1] It was the first transistorized computer, but it was a sizable mainframe and not on the missile. Guidance was by radio control.
The ARMA Micro D is really obscure. It shows up in some lists of early computers. Apparently it was inside some versions of the LTN-51 inertial navigation system.[2][3] But this seems to have been around 1969-1970. The Concorde used that navigation system.
In 1962, Arma created the first microcomputer, or at least the first computer with that name. The Arma Micro Computer was a general-purpose aerospace computer built from transistors and transfluxors (two-hole core memory with a cool name). The computer was a tiny 0.4 cubic feet and 20 pounds. It was a 22-bit machine; while we now think word sizes must be a power of 2, back then people used whatever word size gave them the accuracy they needed.