As Bert Smith explains, when it comes to the Windows XP pagefile, it's not size that matters but what you do with it.

The Windows pagefile, pagefile.sys, is absolutely crucial to Windows' operation. It temporarily holds data that would otherwise be held in memory in order to free RAM up for other applications. Pagefile.sys is created when Windows XP is installed and is stored by default in the root of the partition containing the operating system. Without pagefile.sys, some software won't run, hardware can malfunction and "out of memory" errors can appear on boot up.

If it's too small, the problems mentioned above can occur and XP's performance can become lethargic due to significant disk activity (thrashing). If pagefile.sys is too large, it wastes disk space and can cause file fragmentation.

Using the NTFS file system, full control must be given to the system for the root directory where pagefile.sys is located. If you don't, the "unable to create a pagefile" message appears on boot up.

The first step towards optimising your pagefile is to figure out how much space it should occupy. There is vigorous debate about the size, placement and the necessity of a pagefile. However, one size doesn't fit all in this situation.

Log on to your computer, making sure you have ‘administrator’, and follow these steps to find the locations and sizes of your pagefiles.

Go to Control Panel > System , click on the Advanced tab and under Performance, click Settings. On the Advanced tab under Virtual memory, click Change in Performance Options. The Virtual Memory dialog box opens with the details of the pagefiles on your system and their locations. This is also the place to make changes to your pagefile settings if you want to resize or move them to another disk.

OPTIMUM SIZE

Opinions differ widely for the pagefile size. Microsoft suggests that the recommended minimum size of your pagefile should equal about one and a half times the amount of your physical RAM (http://support.microsoft.com/default.aspx?scid=kb;en-us;308417). It also recommends that a maximum size is about four and a half times the quantity of the physical RAM you have installed. A system with 512MB of RAM would therefore be around 768MB, with a maximum of 2,048MB. The default size of the virtual memory paging file Windows creates during installation is one and a half times the amount of RAM on your computer.

Obviously, a larger pagefile is required for the optimum performance of a system that has plenty of RAM, but this is a contentious issue. In his account of virtual memory, Microsoft MVP Alex Nichol states that the file should be around two and a half times the amount of RAM you

Some experts recommend setting the pagefile to be dynamically sized, but this can slow the disk system down and lead to extra file fragmentation. Others recommend setting the maximum and minimum sizes to the same number, so Windows is locked into using a pagefile of a specific size. Unfortunately, Microsoft has suggested that this hampers rather than improves performance (www.microsoft.com/WindowsXP/expertzone/columns/mcfedries/03junel6.asp).

The best way to choose your pagefile size is by doing a little digging. XP's Task Manager is useful for finding the optimum size for your pagefiles. To do this, load up the applications you usually have running at any one time, adding one or two more for good measure. Right-click the Task Bar, select Task Manager and then choose the Performance tab. There are four number boxes at the bottom of the window, labelled Totals, Physical Memory, Commit Charge and Kernel Memory. Keeping the Commit Charge peak well below the value of the installed RAM reduces the need for the pagefile and makes additional RAM available for the system cache.

<Keep an eye on the difference between the Commit Charge and Physical Memory totals. This should be as large as possible. This box also displays the amount of pagefile usage. If this is a single, flat line, then the system is accessing the pagefile minimally and your system is fine as it is. A deeper, more thorough test involves building your own pagefile monitor.

CUSTOM CONSOLE

It's easy to create a custom pagefile monitor that can run over several days to log data, enabling you to optimise your pagefile. There's also a free Visual Basic program available from Microsoft MVP Doug Knox's Web site, www.dougknox.com/xp/utils/xp_pagefilemon.htm.

To build your own, follow these basic steps. Click on the Start menu and open the Run box. Type mmc into the box and click OK. From the MMC console, click File > Add/Remove Snap-In > Add and the ActiveX Wizard will open. Select ActiveX Component > Add > Next and set the Control category drop down menu to All Categories. Under Control Type, select System Monitor Control > Next. At this point you'll be prompted to name your monitor: "Pagefile Monitor" is a sensible choice. After you've named it, click Finish > Close > OK.

Now you have a snap-in which you can add counters to and monitor. In the right-hand pane of the console, click the + sign in the top row to open the Add Counters dialog box. From here, choose Select counters from computer. Under the Performance object heading, select all counters and select instances from the list. Click Add > Close. This is all you need to do to create the monitor. From here you can drag a shortcut of the snap-in to the desktop to launch the monitor.

Before using it, fire up the apps you usually run, plus one or two that you only use occasionally. To log the data your Paging File Monitor collects, right-click the top bar on the right-hand page, select Properties, choose Source and check the Log files radio button. Text file comma delimited (csv) is a convenient file type. Ensure the log has started before continuing.

After a few days, open the log file with Notepad or Excel. Look for the highest value shown on the far right of each log, and round it up to the nearest whole number. Get the average for all the logs — they're in percentages.

To obtain a suggested initial page size value, divide your average by 100 and multiply it by the size of your current pagefile in megabytes. To be on the safe side, and to prevent running out of virtual memory, add approximately 40% to the value of your calculated figure to work out the ideal pagefile size.

Power tools: If you scratch Windows' surface, secret utilities like MMC snap-ins enable you to construct useful tools.

PLACING THE PAGEFILE

Consider whether you want a small kernel or complete memory dump formed in the event of a system crash. If you do, a pagefile must be created on the partition where Windows XP is installed. A pagefile of fixed size is useful for this purpose. Using the utility dmpchk.exe from the XP installation disc, analysis of memory.dmp can reveal the system state at the time of the crash. However, the results can be difficult to interpret and don't reveal the events leading up to the time of the crash.

XP's built-in disk defragmenter is a cut-down version of Executive Software's Diskeeper and has some severe limitations — for one, it can't even defrag a pagefile. A small performance gain can be obtained if the pagefile is defragmented, so having a dedicated drive/partition for the pagefile is attractive.

Some commercial applications, like Defrag for Windows, can defrag the pagefile, but make sure you back it up before doing so. A fragmented pagefile substantially hampers performance, so it's a good idea to defrag them at least once a month. While paying special attention to your pagefile isn't the be-all and end-all of memory tweaking, sensible and considered settings will ensure your machine can run at full tilt when the going gets tough.