Tuning Windows XP’s Performance : Optimizing Virtual Memory

Storing the Page File Optimally

The location of the page file can have a major impact on its performance. There are three things you should consider:

• Store the page file on the hard disk that has the fastest access time— You’ll see later in this section that you can tell Windows XP which hard disk to use for the page file. If you have multiple hard disks (not just multiple partitions of a single disk), you should store the page file on the disk that has the fastest access time.

• Store the page file on an uncompressed partition— Windows XP is happy to store the page file on a compressed NTFS partition. However, as with all file operations on a compressed partition, the performance of page file operations suffers because of the compression and decompression required. Therefore, you should store the page file on an uncompressed partition.

• Store the page file on the hard disk that has the most free space— Windows XP expands and contracts the page file dynamically depending on the system’s needs. To give Windows XP the most flexibility, make sure that the page file resides on a hard disk that has a lot of free space.

Splitting the Page File

If you have two or more physical drives (not just two or more partitions on a single physical drive), splitting the page file over each drive can improve performance because it means Windows XP can extract data from each drive’s page file simultaneously. For example, if your current initial page file size is 384MB, you’d set up a page file on a drive with a 192MB initial size, and another page file on a second drive with a 192MB initial size.

Customizing the Page File Size

By default, Windows XP sets the initial size of the page file to 1.5 times the amount of RAM in your system, and it sets the maximum size of the page file to 3 times the amount of RAM. For example, on a system with 256MB RAM, the page file’s initial size will be 384MB and its maximum size will be 768MB. The default values work well on most systems, but you might want to customize these sizes to suit your own configuration. Here are some notes about custom page file sizes:

• The less RAM you have, the more likely it is that Windows XP will use the page file, so the Windows XP default page file sizes make sense. If your computer has less than 512MB RAM, you should leave the page file sizes as is.

• The more RAM you have, the less likely it is that Windows XP will use the page file. Therefore, the default initial page file size is too large and the disk space reserved by Windows XP is wasted. On systems with 512MB RAM or more, you should set the initial page file size to half the RAM size, while leaving the maximum size at three times RAM, just in case.

• If disk space is at a premium and you can’t move the page file to a drive with more free space, set the initial page file size to 2MB (the minimum size supported by Windows XP). This should eventually result in the smallest possible page file, but you’ll see a bit of a performance drop because Windows XP will often have to dynamically increase the size of the page file as you work with your programs.

• You might think that setting the initial size and the maximum size to the same (relatively large; say, two or three times RAM) value would improve performance because it would mean that Windows XP would never resize the page file. In practice, however, it has been shown that this trick does not improve performance, and in some cases can actually decrease performance.

• If you have a large amount of RAM (at least 1GB), you might think that Windows XP would never need virtual memory, so that it would be okay to turn off the page file. This won’t work, however, because Windows XP needs the page file anyway, and some programs might crash if no virtual memory is present.

Watching the Page File Size

Monitor the page file performance to get a feel for how it works under normal conditions, where normal means while running your usual collection of applications and your usual number of open windows and documents.

Start up all the programs you normally use (and perhaps a few extra, for good measure) and then watch System Monitor’s Process\Page File Bytes and Process\Page File Bytes Peak counters.

Changing the Paging File’s Location and Size

The page file is named Pagefile.sys and it’s stored in the root folder of the %SystemDrive%. Here’s how to change the hard disk that Windows XP uses to store the page file as well as the page file sizes:

Exit all the dialog boxes. If you changed the drive or if you decreased either the initial size or the maximum size, you need to restart your computer to put the changes into effect.

Defragmenting the Page File

As Windows XP dynamically sizes the page file, it’s possible that it can become fragmented, resulting in a small performance hit. Windows XP manipulates the page file in relatively large blocks, so fragmentation rarely occurs. However, if you’re looking to eke out every last drop of performance on your machine, you should probably ensure that the page file is defragmented.

Unfortunately, Windows XP Disk Defragmenter tool does not defragment the page file. To accomplish this, you have to temporarily move or disable the page file. Here are the steps to follow: