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RAM is a limited resource, whereas virtual memory is, for most practical purposes, unlimited. There can be a large number of processes each with its own 2 GB of private virtual address space. When the memory in use by all the existing processes exceeds the amount of RAM available, the operating system will move pages (4 KB pieces) of one or more virtual address spaces to the computer’s hard disk, thus freeing that RAM frame for other uses. In Windows systems, these “paged out” pages are stored in one or more files called pagefile.sys in the root of a partition. There can be one such file in each disk partition. The location and size of the page file is configured in SystemProperties, Advanced, Performance (click the Settings button).

A frequently asked question is how big should I make the pagefile? There is no single answer to this question, because it depends on the amount of installed RAM and how much virtual memory that workload requires. If there is no other information available, the normal recommendation of 1.5 times the amount of RAM in the computer is a good place to start. On server systems, a common objective is to have enough RAM so that there is never a shortage and the pagefile is essentially, not used. On these systems, having a really large pagefile may serve no useful purpose. On the other hand, disk space is usually plentiful, so having a large pagefile (e.g. 1.5 times the installed RAM) does not cause a problem and eliminates the need to fuss over how large to make it.[1]