There are many things that we take for granted today that weren't decided upon in the early days of computing, like the byte being 8-bits (which was popularized by the System/360) or word sizes being 2^(3+n). Some early machines were bit-serial (imagine an adder operating on one bit at a time, rather than on all of the bits in parallel). Even more fun: the Harvard Mark I and ENIAC were both base-10 machines. I can't imagine the amount of engineering that went into producing a base-10 machine out of inherently base-2 components. (Example: the relays of the Mark I. Tubes are analog, but I'm guessing that any use in computers would only use a high and a low state.) Many machines used sequentially accessed main memory rather than random access memory (the drum memory of the LGP-30 or mercury delay-lines). The list goes on.
The ENIAC components were (or at least some of them were) decimal. Things like tube decade-counters were combined into a computer. They picked components available off the shelf and cobbled it into a computer. I believe such counters were used in stuff like frequency counters before they were used in ENIAC.
