This article was previously published under Q99768
Windows NT uses a paging file for virtual memory called PAGEFILE.SYS.
This file is created during Windows NT Setup and is always located in
the root directory. No matter what your system configuration is,
Windows NT will create and use a paging file.
The paging file is not necessarily a single file; it can be a group of
files stored in various locations, across hard disks and partitions.
The files are collectively referred to as "the paging file." When
thinking about the size of the paging file, the sum of all the files
that make up the paging file is the only value you need to keep in
The following two guidelines should be met when optimizing the paging
- In general, you should set the size of the paging file to the same
size as your system RAM plus 12 MB. There is a minimum size
requirement of 22 MB for the operating system. If system RAM plus
12 MB is less than 22 MB, increase the size of the paging file
until your system RAM plus paging file is at least 22 MB.
NOTE: 22 MB is just what the operating system requires for itself.
For reasonable application performance, a 40 MB total is
These sizes are recommended because Windows NT requires "backing
storage" for everything it keeps in RAM. If Windows NT requires
more space in RAM, it must be able to swap out code and data to
either the paging file or the original executable file. If Windows
NT cannot do this, out of memory errors will be generated.
If you set your paging file to system RAM plus 12 MB and you still
get low memory warnings, try increasing the size of the paging
file. If you need more disk space and you are not getting memory
warnings or memory-related problems, you can try to decrease the
size of the paging file.
Also, if you have enough surplus RAM to support the operating
system and application memory requirements, the need for a large
paging file is lessened. If you have, for example, 64 MB of RAM,
you may be able to safely reduce your paging file to a very small
- If you have multiple hard disks, splitting up the paging file is a
good idea, as it will speed up the access time. If you have two
hard disks, and you split the paging file, both hard disks can be
accessing information simultaneously, greatly increasing the
throughput. However, if you have two hard disks, and one hard disk
is faster than the other, it may be more effective to store the
paging file on only the faster hard disk. Some experimentation may
be necessary to arrive at the best configuration for your system.
Note: There is no point in splitting up the paging file between
multiple partitions as it does not increase the ability of the hard
disk to access the paging file. This may be a good idea, however,
if your logical drives aren't large enough for the entire paging
Article ID: 99768 - Last Review: October 31, 2006 - Revision: 3.1
- Microsoft Windows NT Advanced Server 3.1
- Microsoft Windows NT Workstation 3.1
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