Programming

That was true a couple of decades ago. Nowadays most embedded systems mobile phones for ex. have an OS, virtual memory mgmt and all the libraries. Although the op may be using one that is bare bones but I doubt that otherwise he would not be using malloc and would most likely be coding in assembly language instead of in C.

The actual difference is that the first example copies the address of your pmem pointer to the stack and the second example doesn't. The second example only works because you're using malloc() which allocates memory from the heap, otherwise you could have unexpected behavior because you would be returning a local variable (which is cleared upon function completion).

IMHO the second option would be faster because there's one less parameter to be copied to the stack and there's no desreferencing of the pointer's address to obtain the data. Anyway, you should feel no significant speed difference in any of the alternatives.

I can't see any effective difference aside from the extra complications of effectively returning two values in your first example. I'd tend to avoid that kind of redundancy in case my fumble fingers ever cause one to contradict the other.