It is sometimes useful when debugging to be familiar with the which
pointer values are typically to the static data area, which to the
heap, and which to the stack.  This example shows some typical values.
(The basic idea is that "big" means stack and "small" means static and
"in between" means heap.)

It also shows that both main.c and sub.c agree where in memory
globalInt has been allocated.  The compiler cannot figure out what
that location will be when compiling each file individually -- it's
above the instructions for main and the instructions for sub and it
has no idea how much space those will take together when it's
compiling either one individually (among other problems it would have
trying to figure out where globalInt will be allocated).  The linker
eventually lays out all the instructions (main and sub) and all the
globals (globalInt) and other static data (the string literal).  It
then knows where they are all allocated and can "patch" machine
instructions that needed those addresses.