Originally Posted by DaWei

Don't get your shorts in a wad, I'm not the one putting out insufficient information. I would say you're overestimating people's psychic abilities, not their comprehension.

That said, here's the deal: you can't represent a memory location with 3 bits, unless you have very little memory. Registers aren't (normally) memory. They're storage locations local to the uP. If you have 8 of them, you have a pattern of 3 bits sufficient to identify each one individually.