If things had worked out differently we might be
using
ultraminiature electron tubes. Imagine! An entire flipflop in one
package!
In the '60s I saw a rocket control computer that was used in a high
acceleration missile that was IIRC about 30 cm cubed. It was made up of
layers of ceramic approximately 3-5 mm thick each containing around
50-100 "tubes" separated by a thin 2-3 mm layer of ceramic insulation.
Each "tube" consisted of an Americium cathode, the necessary grids
(perforated plates), and a plate evaporated on the wall of the cavity.
Everything was interconnected by metalization on the insulating layer.
The necessary resistors/capacitors were placed in cavities between the
"tubes".
What made this extremely interesting was that all circuitry was
differential to exclude the common mode voltages that were generated by
the compression of the ceramic block during launch. At that time, solid
state devices self-destructed during the acceleration phase. I imagine
that any "personal" computer made with that technology would
self-destruct any savings one had...
CRC