A. Any program that runs on an Intel 386 or later system can access up to 4GB of RAM, which is typically far more memory than is physically available on a machine. To make up for the missing physical memory, the OS creates a virtual address space, known as virtual memory, in which programs can see their own 4GB memory space. (This virtual address space consists of two 2GB portions--one for the program and one for the OS.) The OS is responsible for allocating and mapping to physical RAM those parts of the program or memory that are currently active.
To work around a machine's physical RAM limitations, a local file known as the pagefile stores pages (in 4KB increments) that aren't in use. (One installation can have multiple pagefiles.) When a program needs to access a page from the pagefile, the OS generates a page fault that instructs the system to read the page from the pagefile and store it in memory. Because disks are much slower than memory, excessive page faults eventually degrade performance. A computer's RAM consists of two sections. The first section, the non-paged area, stores core OS information that's never moved to the pagefile. The second section, the paged area, contains program code, data, and inactive file system cache information that the OS can write to the pagefile if needed.
Although the discussion so far might lead you to believe that Windows stores only active code and data (plus the core OS) in physical RAM, Windows actually attempts to use as much RAM as possible. Often, the OS uses RAM to cache recently run programs so that the OS can start these programs more quickly the next time you use them. If the amount of available free RAM on your computer is low and an application needs physical RAM, the OS can remove from RAM pages of memory used to cache recently run programs or move non-active data pages to the pagefile.
So, if you have a lot of RAM, you don't need a pagefile, right? Not necessarily. When certain applications start, they allocate a huge amount of memory (hundreds of megabytes typically set aside in virtual memory) even though they might not use it. If no pagefile (i.e., virtual memory) is present, a memory-hogging application can quickly use a large chunk of RAM. Even worse, just a few such programs can bring a machine loaded with memory to a halt. Some applications (e.g., Adobe Photoshop) will display warnings on startup if no pagefile is present.
My advice, therefore, is not to disable the pagefile, because Windows will move pages from RAM to the pagefile only when necessary. Furthermore, you gain no performance improvement by turning off the pagefile. To save disk space, you can set a small initial pagefile size (as little as 100MB) and set a high maximum size (e.g., 1GB) so that Windows can increase the size if needed. With 1GB of RAM under normal application loads, the pagefile would probably never need to grow.
If you want to prevent Windows from moving any core OS kernel or driver files to the pagefile, perform the following steps:
- Start a registry editor (e.g., regedit.exe).
- Navigate to the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management registry subkey.
- Set the DisablePagingExecutive registry entry to 1.
If you want to determine how much of the pagefile is actually being used, you can download Bill James' various pagefile utilities, which are available at this Web site. Among these tools is a WinXP-2K_Pagefile.vbs script that tells you the current and maximum pagefile usage.
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Not true according to my experience. Windows 95 and 98 only used the pagefile when necessary. But Windows NT, 2000, XP does use it even when NOT necessary. (And probably also Windows 2003.) The OS seem to free RAM by moving pages to the pagefile even if there is large amounts of unused RAM! I usually se about 20-60MB of the pagefile used for this. Is there a way to tell Windows to ONLY move data to the pagefile when needed?
And another related question…
In Windows 95 and 98 there was a setting in system.ini which you could use to specify the maximum size for the filecache. This was very useful because it stopped Windows desktop, i.e. explorer.exe + loads of dll-files being swapped out when doing a normal copy of a large file.
Example:
Computer with 512MB of RAM.
Windows uses 100MB of RAM after startup.
I copy a 1GB file.
Windows uses all available RAM, 512MB for filecache, causing almost everything but non-paged pool being swapped out to the pagefile.
After file copy, trying to open a folder in explorer takes ages to load!
However, if you reserve 128MB of RAM by setting system.ini to:
[vcache]
MinFileCache=4096
MaxFileCache=393216
Now you don’t have any delays double-clicking folders, opening start-menu, or whatever you do on the Windows desktop.
Is there a way to specify how large the filecache may grow in Windows NT, 2000, XP and 2003?
Best regards,
Daniel Mukka Nyberg
Daniel Mukka Nyberg March 18, 2004