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by jreck 2823 days ago
> Your statement is equivalent to saying "there's no difference between pointers and integers" - technically, they are both just numbers that live in registers or somewhere in memory. In reality, that approach will not get you far in computer science.

No, because in reality those are handled by different computational units. Integers are handled by the ALU, and pointers are handled by the loader. They are distinct things to the CPU.

Stack & heap have no such distinction. There isn't even a heap in the first place. There's as many heaps of as many sizes as you want, as the "heap" concept is an abstraction over memory (strictly speaking over virtual address space - another concept C won't teach you, yet is very important for things like mmap). It's not a tangible thing to the computer.

Same with the stack. It's why green-threads work, because the stack is simply an abstraction over memory.
2 comments
temac 2823 days ago
> No, because in reality those are handled by different computational units. Integers are handled by the ALU, and pointers are handled by the loader. They are distinct things to the CPU.

I strongly disagree. Yes some execution units are more let's say "dedicated" to pointers than other, and obviously ultimately you will dereference your pointers, so you will load/store, but compilers happily emit lea to do e.g. Ax9+B and in the other direction, add or sub on pointers. Some ISA even have almost no pointer "oriented" register (and even x64 has very few)

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arcticbull 2823 days ago
Exactly, this will vary wildly between architectures. I would accept the statement on, for instance, a Harvard architecture but the world is a lot more nuanced in the much more common von Neumann architecture.
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arcticbull 2823 days ago
No no, haha, that's also not quite right. You can save the stack frame to memory then load it back which is what green threads do [1]. This includes the register state also, which is not what we're talking about here when we say "stack" -- we're referring to stack variables, not full frames. Full frames are even further from the heap, by virtue of including register states which must be restored also.

Although, it sounds like you're agreeing with me that there is in fact a difference between the stack and the heap because to your point one exists supported at the hardware level with instructions and registers, and one doesn't exist or can exist many times over. Hence, different.

[1] https://c9x.me/articles/gthreads/code0.html

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