"registers" of course I do, I was just trying to simplify it. Wasn't it IX, IY and A? I'll google ...
Inside every Commodore 64 is a MOS 6510 processor, the big brother to the 6502 that is used in the VIC-20 and most disk drives. This processor has three registers that can be used for many purposes. They are, the accumulator, denoted here as ".A", the X Index Register, denoted as ".X", and the Y Index Register, denoted as ".Y".
source: http://www.go64.de/english/online_e/04_99_1e.htm