The 6502 had no concept of not doing a memory operation. Either it's doing a read or it's doing a write, there is no option to use the bus unused. So the 6502

The 6502 had no concept of not doing a memory operation. Either it's doing a read or it's doing a write, there is no option to use the bus unused. So the 6502 spams dummy reads and occasionally dummy writes whenever it's doing something internally. Edit: And that's not the only interesting thing I've learned recently about the 6502, There is a very good reason why the stack is on page 1 and not some other constant page. There are only 3 constant values which can be pushed on the SB/ADH buses, 0xff, 0x00 and 0x01. Ox00 is loaded into upper address register for zero page instructions. For Push operations, it loads 0x01 into the upper address register and puts the stack pointer + 0xff into the adder, which subtracts one from the stack pointer. (The 0xff is just the default bus value, if nothing else is pulling it low, so you get it for free) For Pop operations, it pushes the same 0x01 into both the upper address register and the adder, at the same time. So if they wanted to put the stack page at another constant page, or at a variable page they would also need to provide more gates to provide another constant one somewhere.