Microsoft KB Archive/83968

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How Windows Determines the Recommended Maximum Swap File Size

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Q83968

3.10 3.11

WINDOWS

kbusage

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The information in this article applies to:


 * Microsoft Windows versions 3.1, 3.11
 * Microsoft Windows for Workgroups versions 3.1, 3.11

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SUMMARY
This article discusses how Microsoft Windows version 3.1 determines the file size to recommend for swap files.

Temporary Swap File
 Q. What is the temporary swap file recommended maximum size?

A. It is four times the physical RAM in the computer, rounded to the next 4 megabytes (MB). For example, if you have 3 MB of free XMS memory, you can create 16 MB of virtual memory ([3 MB * 4] + 4MB = 16 MB). Four is the default value for the SYSTEM.INI [386Enh] switch &quot;PageOverCommit=&quot;. The recommended maximum size is also limited by the &quot;50 percent free hard drive space&quot; rule (that is, a swap file cannot take more than 50 percent of the available, usable hard drive space [compressed or stacked hard drive space is not considered usable]).

Whichever limit is reached first establishes the maximum size.  Q. When I set a temporary swap file to a size larger than the maximum recommended size, the following error message is displayed. What does this message mean?

Windows will not use more than the virtual memory specified by the Recommended Size. Are you sure you want to create a larger swap file?

A. WIN386.EXE creates the temporary swap file at run time, and the file grows as necessary; the swap-file functionality only controls the maximum size allowable. You can never exceed 50 percent of the free hard disk space or four times the amount of physical RAM. 

Permanent Swap File
  Q. When I set a permanent swap file to a size larger than the recommended maximum size, Windows forces the setting back to the recommended maximum size, even when plenty of free hard drive space exists. When this occurs, the following message is displayed. What does this message mean?

The number you specified is too large. The number currently displayed is the largest you can specify.

A. When Windows sets up a permanent swap file, free and contiguous hard drive space limits the recommended maximum size. A permanent swap file must be located on unfragmented space; therefore, even if there is plenty of disk space, the swap file is limited by file fragmentation. 

If you have an disk-optimization program, such as Speedisk by Norton Utilities or Compress by PC Tools, you can use it to make more of the free hard drive space contiguous and usable for a permanent swap file.

NOTE: The maximum size limitations described in the first answer apply in addition to the required unfragmented disk space.

NOTE: These utilities should not be run from Windows and should not be run if you are using a disk cache. For more information, consult the manual for the utility you are using. KBCategory: kbusage

KBSubcategory: wfw win31 wfwg

Additional query words: 3.10 3.11 unfragment defragment swapfile

Keywords : win31

Issue type :

Technology : kbAudDeveloper kbWin3xSearch kbWFWSearch kbWin310 kbWin311 kbWFW310 kbWFW311