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1111-11 = 64 combinations,
2^2 x 4^2 = 64 (binary) combinations.
A computers CPU starts with 2 bits, a + and a -. These get stored temporarily in the BUS as 4 x 'ons and offs'.
These four data structures get passed to on-board CPU Cache to build the command. If the cache is 64-bits wide, due to the registering, 2x2x2x2(4^2)x2x2(2^2) ons and offs get passed to the cache. This cache then links to the command needing execution, usually a mov or call, to process data or code in RAM.