PRB: Windows 95/98 Heaps Have A 255.9 MB Allocation Ceiling

• Microsoft Win32 Software Development Kit (SDK)
  on the following platforms: Win95, Win98

SYMPTOMS

There is a hard-coded limit on Windows 95/98 for a single heap allocation. This limit is 104 bytes shy of 256 MB.

This limit will apply to HeapAlloc() and any function that internally calls HeapAlloc(); including LocalAlloc(), GlobalAlloc(), and many implementations of the C-runtime library's malloc() function.

STATUS

This behavior is by design.

MORE INFORMATION

If you expect your memory blocks to be larger than one or two megabytes, you can avoid significant performance degradation by using the VirtualAlloc() or VirtualAllocEx() functions instead. When working with the heap functions, memory allocations are classified into the following three block size ranges:

• 0 - 4 MB


The heap functions work well for allocations in this range.


• 4 - 255.9 MB


The heap functions work for allocations in this range, but they are not recommended due to poor performance.


• 255.9 MB and up


The heap functions do not support allocations above 255.9 MB.

Additional query words: kbDSupport

Keywords          : kbKernBase kbMemory 
Version           : WINDOWS:
Platform          : WINDOWS 
Issue type        : kbprb 

Last Reviewed: April 15, 1999