Get the most out of Windows NT's paging file

The paging file is one of the most important files on the Windows NT system. If you feel like you're not making the most of this vital file, find out how to change its size and location, and get some best practices for choosing its placement.

Also known as the swap file, the paging file is one of the most important files on the Windows NT system. Without this file, the system would still boot, but it would appear to be standing still instead of running.

Think of the paging file as an extension of the computer's memory. When several applications run at the same time, more memory is often necessary than what the computer actually has. When this happens, the operating system copies the applications that currently aren't running to a file on the disk, thereby freeing up memory for running applications.

By default, Windows NT creates this file on the system drive and names it Pagefile.sys. While you can change the size and location of this file, you can't modify its name.

To change the size or location of Pagefile.sys, follow these steps:

  1. Open Control Panel, and double-click the System applet.
  2. On the Performance tab, click the Change button.
  3. In the resulting Virtual Memory dialog box, change the file settings as needed, and click OK.

Optimize the paging file

In order to optimize the paging file with total system performance, you must choose its size and location correctly. While there's no universal solution to paging file optimization, you can monitor its usage with either Task Manager or Performance Monitor.

Task Manager displays several memory counters on its Performance tab. Check to make sure that the three counters under Commit Charge (K) display the total amount of memory available to your programs (which is actually the RAM plus the paging file).

To find out how much memory your applications are using, look at the Peak counter. The rule of thumb is not to let the Peak get close to Limit. When it does, an error message will pop up, and you'll have to enlarge the paging file and/or add more RAM.

Using Performance Monitor, you can keep an eye on the paging file's % Usage and Usage Peak (bytes) counters, listed under the Paging File object. The first counter displays the current usage in percentages, and the second displays the peak usage over a given period of time.

While both utilities show you how your system is using the paging file, Task Manager is the simpler of the two. However, Performance Monitor's advantage is that you can log its counters in a file, determine how usage is increasing, and make some predictions for the future.

Optimize the file's placement

The placement of the paging file is also an important decision. A properly placed paging file can give your computer a performance boost.

It's also possible to have more than one Pagefile.sys. If a computer has several hard drives, you can create additional paging files. In fact, you can place a paging file on each partition.

However, depending on your system's setup, this can have either good or bad side effects. For optimal performance, it's best to have three fast hard drives—one to hold the operating system files and the other two for paging files.

Here are some best practices for paging file placement:

  • If your system has two hard drives, place Pagefile.sys on the disk that doesn't contain the Windows NT files.
  • If your system had more than two hard drives, place paging files on all disks, except the one that stores Windows NT system files. Windows NT will use load-balancing between all of the paging files.
  • If your system has several hard drives with unequal performance, place Pagefile.sys on the fastest hard drive.
  • If your system has only one hard drive with several partitions, place Pagefile.sys on only one partition. If you place it on several partitions, the performance of your computer will suffer.

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