Storage Classes

There are three places in memory where data may be placed: in the data section (declared with .data in assembly language), on the run-time stack, and on the heap.

A subroutine other than main() can have data in the .data section. In high-level programming languages, such as "C", this type of storage is called static.

Variables whose storage is allocated on the run-time stack are (sometimes) called automatic variables. This is because their storage is "automatically" pushed and popped as a subroutine is entered and exited. Usually the word "variable" means "automatic variable".

A variable whose memory is located in the heap is called a dynamic variable. These notes only briefly deal with the heap. The heap is where memory for objects is found (using the new operation in Java or C++). In "C" dynamic memory is allocated using the malloc operation (or similar).

The heap is on top of the data segment. As dynamic variables are created it grows upward (towards the stack)