Out of curiosity, I checked wikipedia which says "In the 6600, loading the value from memory would require one instruction, and adding it would require a second one" so I'm curious what the distinction is if it's not a load instruction
The address registers were paired up with the data registers, so modifying A1 would cause an implicit load into X1, for example. A6 and A7 modifications caused implicit stores from X6/X7. So with careful register assignment and some offset initialization of address registers beforehand, array processing loops could be encoded in remarkably few instructions.
