Windows 3.11 Permanent Swap File Size Setting

In Microsoft Windows 3.11, the system parameter that controls the maximum allowable size of a permanent swap file is PageOverCommit. Located within the SYSTEM.INI configuration file, this setting works in tandem with installed physical RAM to calculate the upper limit of virtual memory. This article explains how the PageOverCommit parameter functions, how it establishes the swap file ceiling, and how to configure it.

The PageOverCommit Parameter

In 386 Enhanced Mode, Windows 3.11 uses swap files to provide virtual memory. While a permanent swap file requires contiguous, uncompressed disk space, Windows imposes a maximum size restriction based on the system's physical memory.

The parameter responsible for this limit is:

[386Enh]
PageOverCommit=4

How PageOverCommit Determines File Size

By default, the PageOverCommit value is set to 4 (even if it does not explicitly appear in SYSTEM.INI).

Windows calculates the maximum total virtual memory capacity using the following formula:

\[\text{Total Virtual Memory} = \text{Physical RAM} \times \text{PageOverCommit}\]

Because total virtual memory includes both physical RAM and the swap file, the maximum possible size for the permanent swap file is roughly calculated as:

\[\text{Max Swap File Size} = \text{Physical RAM} \times (\text{PageOverCommit} - 1)\]

For example, on a machine with 8 MB of RAM using the default value of 4, the maximum virtual memory space is 32 MB, allowing for a permanent swap file of up to approximately 24 MB (assuming sufficient contiguous disk space is available).

Modifying the Setting

To increase or decrease the maximum allowed swap file size beyond the default four-to-one ratio:

  1. Open the SYSTEM.INI file in a text editor like Notepad or the MS-DOS Editor.
  2. Locate the [386Enh] section header.
  3. Add or modify the line PageOverCommit=<n>, where <n> is an integer value (typically between 1 and 20).
  4. Save the file and restart Windows.

Increasing this value allows the Virtual Memory Control Panel applet to allocate a larger permanent swap file, provided the hard drive has adequate contiguous, unfragmented free space.