How does the program know if a piece of memory is occupied or free?

Question

RAM

How does the program know if a piece of memory is occupied or free?
For example, in a C program, the malloc function allocates memory and returns a pointer to a piece of memory.
I mean a piece of memory in the address space of the program, and not the address on the physical memory module.

Answer 1

The program does not learn anything and should not, the OS allocates memory.