Virtual memory is a system that virtualizes all access to memory. Applications never access physical memory directly but only via the memory management hardware of the processor. This provides a virtual environment to applications that is independent of the size of RAM.

The pagefile was designed to optimize the use of RAM. It does this by temporarily storing rarely used data, thus making RAM available for more important purposes. This improves performance.

Regarding pagefile configuration:
In the large majority of cases the default configuration will be optimum, or as close as to make no difference. Unless you have a very good reason to change it, leave it alone. To make intelligent changes you will need far more information than is in this article.

For the most part the comments by Martin do not correspond with reality and should be ingored.

Larry Miller
Microsoft MCSA

However, Setting the pagefile to a fixed size can give a performance increase over the Automatic resize option. This will also cause your pagefile to be less prone to fragmentation.

The 1.5 x System RAM rule is a good rule of thumb but I wouldn’t advise going above 4Gb as Windows is not to clever when it comes to mapping larger ammounts of memory.

Setting the lower value for the pagefile at 1.5 times the size of physical memory is not necessarily optimum. If memory is short this may be too low, if you have 2GB or more it may be excessive. But as a general rule it isn’t too far off.

But setting the upper limit the same as this – that is a really bad idea. This is most certainly NOT what Microsoft recommends. Doing so may result in out of memory errors or severe performance degradation.

Microsoft recommends that the upper limit be much higher than the lower value, allowing the pagefile to grow when needs are high. The default settings will provide for this. If the lower value is adequate for normal needs this will NOT produce pagefile fragmentation. If the lower value is exceeded the page file will be restored to this value at next reboot (or sooner).

Best recommendations.
If you are an experienced user you may wish to experiment with other values for the lower value. Do not go lower than the size of physical memory. The upper limit should be at least double this value.

An inexperienced user should leave the settings on default. Many very experienced users do this as well. Only change the default settings if you are thoroughly familiar with the implications. You need far more informaton than is contained in this article or my comments.