>I guess an alternative solution would be to put the stacks in different address spaces somehow, but that could get very complicated (now you have two kinds of

>I guess an alternative solution would be to put the stacks in different address spaces somehow, but that could get very complicated (now you have two kinds of pointers). Are there any old systems that had separate heap and stack address spaces? On 16-bit x86, memory was divided into 64K segments and you could have separate ones for code, data and stack. Having effectively a different address space for code isn't a problem, but languages like C expect that you can pass around pointers to stack variables as well as global/heap ones. So now every data pointer needed to be a "far" one (32 bits, segment:offset), and to dereference it the segment portion would usually have to be loaded into the single "extra" segment register that isn't dedicated to code/data/stack. With data and stack sharing the same segment, you could use 16 bit pointers for everything and the code was a lot more efficient.