How to Increase Windows NT System and Desktop Heap Sizes

Last reviewed: September 29, 1995
Article ID: Q125752

The information in this article applies to:

Microsoft Win32 Application Programming Interface (API) included with:
```
    - Microsoft Windows NT version 3.5
```

SUMMARY

Sometimes, it may be necessary to increase the amount of memory that Windows NT will make available for the system and desktop heaps. This can be accomplished by editing an entry in the registration database. System heap items are things like desktops and one-time-allocated items like system metrics. The items that come out of the desktop heap are items such as windows, menus, hook structures, queues, and some thread information.

MORE INFORMATION

The entry to be edited is under:

HKEY_LOCAL_MACHINE\

   System\
   CurrentControlSet\
   Control\
   Session Manager\
   SubSystems\
   Windows

Under this entry, you will find a string similar to the following (the slash (/) is a line continuation charater):

%SystemRoot%\system32\csrss.exe /

   ObjectDirectory=\Windows /
   SharedSection=1024,512 /
   Windows=On /
   SubSystemType=Windows /
   ServerDll=basesrv,1 /
   ServerDll=winsrv:GdiServerDllInitialization,4 /
   ServerDll=winsrv:UserServerDllInitialization,3 /
   ServerDll=winsrv:ConServerDllInitialization,2 /
   ProfileControl=Off /
   MaxRequestThreads=16

By changing the SharedSection values, you can affect the heap sizes. The first number (1024 as shown above) is the maximum size of the system wide heap in kilobytes. The second number (512 as shown above) is the maximum size of the per desktop heap in kilobytes. A desktop value of 512K can support approximately 2,500 windows.

The memory you allocate needs to be backed up by paging space. It should not have much effect on performance if you create the same number of items with different heap sizes. The main effect is overhead in heap management and initialization.

Additional reference words: 3.50
KBCategory: kbui
KBSubcategory: UsrWndw

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Last reviewed: September 29, 1995
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