Gonna guess this is related to what he's talking about: https://en.m.wikipedia.org/wiki/Shift_register

They actually move bits of data in and out of the CPU/ram once per 'tick' of the system-wide clock, which is usually ticking in the GHz range.

Software will handle decisions on what bits/bytes to move where, the registers are where data is electronically modified, the shifters actually move the bytes in and out.