System stack

The system stack (a.k.a. call stack or just "the stack") is a place in memory for things that the heap doesn't cover. The system stack is more organized than the heap since it uses the stack data structure, where order matters. Also, the address of the next allocation is known at all times because of this organization. Allocated items are pushed on to the stack in a particular order and popped off when needed.

Most importantly, the system stack is used to store information about subroutine calls (where it gets the name "call stack"). The stack stores parameters for the function and a return address where the program should pick up when the function is finished. It also reserves a space for a return value to be popped by the system on return. Because of its limited size, a stack may "overflow" if too many function calls are made without returning. This situation is dangerous because, if not handled properly (usually by the program stopping and freeing all of its memory), the stack could intersect and overwrite other memory from the program, other programs, or the operating system.