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Q10641: Heap and Stack Usage Within Windows

Article: Q10641
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.0,3.1
Operating System(s): 
Keyword(s): kb16bitonly
Last Modified: 06-NOV-1999

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The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) versions 3.0, 3.1 
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SUMMARY
=======

The following information clarifies heap and stack usage within a segment versus
heap and stack usage within the application as a whole, for Windows versions 3.0
and 3.1.

MORE INFORMATION
================

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:

  handle and limit and globalalloc and register


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.

Additional query words: 3.00 3.10

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Keywords          : kb16bitonly 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK300 kbWinSDK310
Version           : WINDOWS:3.0,3.1

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