(long post... deleted + redrafted behind CW, sorry!)

An #abacus seems very #permacomputing.

It is frequent to use spare columns to hold intermediate results during a long computation. So... a small abacus is an accumulator machine and a larger one that holds several results is more like a stack machine.

The cpu microcode, like multiply/divide algorithms, are memorized by a human. Lots of microcode can be found here: http://totton.idirect.com/abacus/

The programs (breaking down your task into math operations) can be come up with on the spot, written on paper, or they can also be memorized if you do them frequently enough.

The biggest thing missing here is RAM, which could also be used for stored programs. I've seen this done with paper, for machines like the CARDIAC: https://en.wikipedia.org/wiki/CARDboard_Illustrative_Aid_to_Computation.

Scaling up my abacus to a matrix of 100x10 Abacus-style digits would fit in a 50x25 inch desktop frame and yield 1,000 decimal digits or ~500 bytes of RAM.