Heap and Stack Usage Within Windows

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An application gets a single default data segment, from which the stack is allocated. The remainder of the data segment is used for static data and the dynamic local heap.

The STACKSIZE keyword in the .DEF file specifies the size of the application's stack; it is allocated from DGROUP and therefore is limited to a maximum size of (64K - heap size - static data) bytes. The stack size is not dynamically enlarged or reduced.

The HEAPSIZE keyword in the .DEF file specifies the initial default local heap size. Windows attempts to enlarge the heap size when local allocations fail; however, the heap is limited to a maximum size of (64K - stack size - static data).

The sum of the static data, stack, and local heap cannot exceed 64K.

Multiple local heaps can be managed using the LocalInit() call and swapping the DS register as needed. For more information on this technique, query on the following words: Chapter 18 (pages 707-724) of "Windows 3.0 Power Programming Techniques," by Paul Yao and Peter Norton (Bantam Computer Books), contains more details about this technique.