Configuring the Windows registry: Setting the threshold for de-committing memory

If the parallel engine is installed on a computer that runs Microsoft Windows Server, Standard or Enterprise edition, set the threshold for de-committing memory. On computers that have 1 GB or more of RAM, setting the threshold to the suggested value improves memory management.

Before you begin

  1. Log in to Windows Server as the Administrator.
  2. Start the Registry Editor, and back up the Windows Registry. If you plan to make several changes (for example, to configure the parallel engine), create a single backup before you make all the changes.

About this task

When Windows frees memory at a specific address, the memory can remain committed, or it can be de-committed and marked as reserved. You can improve memory management on computers that have 1 GB or more of RAM by editing the HeapDeCommitFreeBlockThreshold registry value in the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager registry subkey. This registry value specifies the number of contiguous bytes of memory (around the address of the freed memory) above which the block of memory is de-committed.


  1. In the Registry Editor, select the following registry subkey:
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager
  2. Specify the value data for HeapDeCommitFreeBlockThreshold registry value:
    1. If the registry value does not exist, click Edit > New > DWORD Value, and type the name of the registry value.
    2. In the right pane of the Registry Editor, right-click the registry value, and click Modify.
    3. In the Base area, select Hexadecimal.
    4. In the Value data field, specify 0x00040000.
    5. Click OK.

What to do next

After you make changes to the Windows Registry, restart Windows to apply your changes. If you plan to make several changes (for example, to configure the parallel engine), make all changes before you restart Windows.