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Limiting Available Memory

An application might appear to generate a negligible number of hard page faults when it is run on a computer that has few other processes running and therefore ample available memory. The performance of the application might degrade, however, with other processes running and reduced amounts of available memory. To test this case, limit memory by using MAXMEM.

Using MAXMEM in Boot.ini

You can use the MAXMEM parameter in the Boot.ini file to set the maximum physical memory available to Windows XP Professional. Boot.ini is a hidden, read-only system file.

To make changes to Boot.ini

  1. To view boot.ini in the root directory:
    1. In Windows Explorer, on the Tools menu, click Folder Options, and then click the View tab.
    2. Clear Hide protected operating system files check box.
    3. Under Hidden files and folders, select Show hidden files and folders.
    4. Click OK.
  2. To remove the read-only attribute of Boot.ini:
    1. In the root directory, right-click Boot.ini.
    2. Clear Read-only.
    3. Click OK.
  3. To edit Boot.ini:
    1. Before making any changes, make a copy of Boot.ini.
    2. Open the Boot.ini file with Notepad.

      An example Boot.ini follows:

      [boot loader]
timeout=20
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /fastdetect
    3. Copy the boot option line (the line under [operating systems]) and paste it immediately below the existing line.
    4. To identify the option when your computer starts, type descriptive text within the quotation marks on the new line. For example: 
      multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional 32MB" /fastdetect
    5. At the end of the line leave a space, and then type /MAXMEM= n (where n is the amount of memory in megabytes that you want to make available to Windows XP Professional).

      Caution: Do not set the amount below 32MB, or Windows XP might not start.

      For example:

      multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional 32MB"/fastdetect/maxmem=32
    6. Reboot your computer, and then choose the new option you created from the boot option lines. Check About Windows or Task Manager to ensure that the change you want is in effect.

  4. Note

    • MAXMEM works only on x86-based platforms. This information does not apply to RISC computers (DEC Alpha, MIPS, and Power PC) that store their boot options in ARC firmware.

Determining the Amount of Available Memory

  1. Open Task Manager.
  2. Select the Performance tab.
  3. Wait until the amount of available memory is at a minimum, and then run the application you want to test. Available memory is listed in the Physical Memory area.

Getting Symbols

To get debugging symbols with Dbghelp.dll, you must install the debugging symbols. Next, set the _NT_SYMBOLS_PATH environment variable to the symbol installation path.