This is not only an excellent answer but also a fantastic history of the development of the stack. > "I've found no particular evidence that the stack pointer

This is not only an excellent answer but also a fantastic history of the development of the stack. > "I've found no particular evidence that the stack pointer was made a full 16 because they felt any need for a stack to be that large. It's clear that at least some experienced microprocessor developers (the MOS 6502 team) felt that an 8 bit stack pointer (256 byte stack) was plenty. It's possible that the 8080 designers disagreed, or it's possible that they felt they couldn't force a particular area to be RAM, as the 6502 designers could. (Even more than the MC6800, the 6502 design strongly encouraged page $00 to be RAM, so forcing page $01 to be RAM was no hardship.) Or perhaps it just didn't occur to them that registers pointing into memory could be any less than 16 bits." To add a little bit of detail to the preceding paragraph: A page in 6502 parlance is a contiguous block of 256 bytes in address space. Page $00 are the first 256 bytes of address space, page $01 are bytes $0000 to $00FF and so on. Page $00 (so called zeropage) is treated specially by the processor and is therefore required to be backed by RAM (not ROM or IO). The 6502 has an 16 bit address bus but only an 8 bit stack pointer. The stack was fixed at 256 bytes (a page) in size and fixed in location at $0100-$01FF (page $01). So the point made above is that because the 6502 already required the zeropage to be RAM it was easy to require the RAM for the stack in a fixed place too, while the designers of other contemporary processors didn't have that luxury.