Page File - Virtual Memory

A page file is used with computer operating systems that support virtual memory management.  The following article addresses these concepts.  The main objective is to provide clear descriptions and to provide recommendations for optimal performance.  Due to the complexity of this subject matter we strongly suggest you research and investigate areas when necessary.  We have provided some links where applicable.

For a greater understanding of virtual memory, see the article here.  In general terms, virtual memory is a method of temporary data storage used by Microsoft computers.  Data is kept on a physical storage device, the hard disk drive, and then brought to “main memory” (also known as RAM – random access memory).  In order to do this unique addresses are assigned to data locations and to areas in memory.  The system relies on a mapping technique in order to sync up one address location with the other.

A page file is a particular area that holds data, instructions, or a combination of these two.  When data is required for use, the operating system will take the required information, and corresponding addresses, and create a set of units referred to as “pages”.  The act of paging refers to transferring page files between memory and hard disk storage.  The page file is regenerated each time you start your computer.

By doing this the system takes advantage of having necessary information on hand in RAM which is faster than accessing it on physical storage.  You might ask, why not keep it in RAM?  The reason is that RAM is “volatile” memory – it is flushed clear when you turn off your computer.  The kinds of applications you can run and the number of programs you can run at one time is affected by how much RAM you have on your system.  This is why good software manufacturers include recommendations on what system requirements are needed to run a software program.

A Brief History

Virtual memory was first used with the introduction of Windows 3.x systems.  Windows 3.0 came out in May 22, 1990.  It was called a “swapfile” and had a filename of WIN386.SWP or 386SPART.PAR.  Along with all system files, these files were hidden from view unless you modify the default settings.  Windows 95 makes use of a similar file which can be accessed in the System settings.  Instructions for doing this are provided below.  

You can view hidden files by doing the following:

1. Open Windows Explorer and click the Tools menu.
2. Select Folder Options.
3. Click the View tab and select the Show hidden file and folders option.
4. Click OK.

When Microsoft released NT operating systems, specifically Windows 2000 and XP, they introduced the page file: “pagefile.sys”.  The file can be found by default on the drive where the system files were installed.  The evolution of the pagefile brought improvements.  The difference between it and its predecessor is that page files move portions of an application process where swapfiles transfer the entire process.  Another distinction is that page files are a pre-emptive solution where swapping happen when a heavy demand is placed on the system.

Problems, Faults, and Errors…

Despite the advantages of using a paging system – speed being the primary one – issues do occur.  The most common relates to page fault errors.  Page faults can be valid or invalid and are caused by a variety of conditions and factors.  To better understand this, we will refer again to a description of computer functionality.  When a program is running and there are other programs running in the background, only the information that is actively required needs to be moved to RAM.  Other information in RAM can be paged out (or swapping can occur depending on what operating system you are using).  When the information that has bee paged out is required and is not found in RAM an interrupt is experienced known as a page fault. 

When these issues occur the system attempts to resolve it.  If a resolution is found by the system the error is considered a valid fault error.  You will likely not have noticed anything happening as the system transfers control back to the running program.  However if the page cannot be found an invalid page error is encountered and you will likely see an error message.  Error messages include:

Windows 3.0: “Unrecoverable Application Error”

Windows 9x: “Illegal operation”

Windows XP: “<Application name> has encountered a problem and needs to close.”

Windows Vista: “<Application name> has stopped working / is not responding.”

In more serious situations involving system functioning, a stop error could result.  When this happens you will experience a blue screen with an error message and information, also known as a “Blue Screen of Death”.  Alternatively your system could automatically restart as seen with Windows XP systems where it is set to restart by default.  See our Stop Error article for more information.  There is area in RAM designated as a non-page section as it contains code that pertains to the system core.  If you get a “Page Fault in Non-Paged Area” message it could mean that there is damage related to accessing code on an area of a potentially defective disk drive.  It could also mean that a RAM module is defective.  In this latter case, you can download and run the Memtest86 diagnostic tool: http://www.memtest86.com/.

Typically invalid page faults are errors occur when an application is running and the system cannot find the data in memory.  Also, errors occur as a result when the table with the address mappings or the area related to virtual memory becomes corrupt.  Other possible reasons include:

-          writing to a read-only page

-          attempting to access a page that has a address space that is not allocated

-          attempting to access a page on standby

-          attempting to write to page that is copy-on-write

-          executing program code that is designated as “no execute”

General protection faults are a common subset of page faults.  While there is a considerable variation of conditions that can bring on these errors, they are generally due to virtual memory instability.  This is commonly the result of a shortage of free disk space or RAM.  The page file is used as a type of overflow mechanism so as to be able to deal with more data than what can be handled by the existing memory specifications.  It requires storage for the overflow.

Performance and Tweaking

Now you have a general idea of the page file and resulting faults than can occur.  Some of these issues require that you go online and search for information that will uncover the contributing factors.  A lot of online resources speak to adjusting the settings of your virtual memory system so as to enhance the performance of your computer.  There are several considerations for a user to make including: should I use a page file, where should I place the page file, how big should it be, how can I make adjustments to the file, and more.  We will cover these in some detail. 

Should I use a page file? 

You can turn off the page file or set the limits so that it is effectively not used.  Some users may feel that they have a lot of RAM and that they want to improve performance when they use an application by only using RAM and not a paging system.  This may be realized if they do not have multiple applications vying for RAM resources.  Sufficient RAM is necessary beyond what any one application requires.  Microsoft “strongly recommends” to “…not disable or delete the paging file.”

Where should I place the page file? 

The general answer to this is to place it where the most activity related to your stored data is likely to take place.  For example, if you have only a C: drive than there is no option – it has to be on this drive.  If you have more than one physical hard disk drive then you want to place the page file where most of your data resides.  The reason for this relates to “seek times” – the time that it takes for a hard disk to locate stored data.  It takes longer for the computer to switch from one hard drive to another so it is best to keep the activity on one hard disk. 

Keep in mind that performance gains will occur only when using a separate physical drive and not by using this technique with a partitioned drive on the same physical drive.  Microsoft concurs that the page file should be placed on a different drive than the one with the system files.  They also state that you should not put the file on a fault-tolerant drive like a RAID-5 drive or a mirrored volume.  Page files do not require fault tolerance and these drives are typically slower.

How big should the page file be?  

There is contradicting information available on the Internet about how big the page file should be.  There are those that recommend keeping the Initial and Maximum size limits the same so as to prevent the file from becoming fragmented.  But is fragmentation an issue?  If your system is frequently using more memory than what it can accommodate (in other words a lack of RAM that is placing heavy demands on the paging functionality), then occasional defragmentation of the page file is recommended.  However, we recommend that you consider dealing with the symptoms as mentioned below – specifically RAM and excessive application use. 

Microsoft recommends that you do one of two things with respect to page size: have Windows select the best page file size or use set the size limits based on how much RAM you have on your system.  To describe these in detail we will need more instructions.  These directions apply to Windows XP and may work on other systems.  However, you may need to do more online investigation applicable to your computer

Privileges

As Microsoft points out (http://support.microsoft.com/kb/308417/), you need to have administrator privileges to make certain changes to your system settings.  With the required privileges, you can access the System settings by doing one of the following:

-          Right-click on the My Computer icon on your desktop, select Properties, and click on the Performance tab

-          Click the Start button, select Settings | Control Panel | System, and selecting the Performance tab.

RAM – Determining How Much You Have

To determine the amount of RAM your computer has do the following:

1. Right-click the My Computer icon on your desktop
2. In the General tab you can see in the section on “Computer” information related to your CPU and RAM.
3. Make a note of how much RAM is being used.

Changing Page File Settings

With the System Properties dialog open you can access the page file settings.  If you have not been able to access the System properties as in the last set of instructions you can do the following:

1. Click the Start button and select Run.
2. In the Open field type: sysdm.cpl
3. Click OK.

To view the page file settings do the following in the System Properties dialog:

1. Click the Advanced tab.
2. In the Performance section, click the Settings button.
3. In the Performance Options dialog select the Advanced tab.
4. In the Virtual Memory section click the Change button.

Microsoft recommends that you select the “System managed size” option which means that your computer will determine how much paging it requires.  The other recommendation they provide is to have an Initial size of 1.5 times your RAM and a Maximum size of 3 times your RAM.  You can use the RAM notation you wrote earlier and a calculator to come up with these figures.  Before you set these values you need to decide whether the Microsoft recommendations work for you and your system. 

If you use a lot of RAM – 1 GB or more – you may want to consider a smaller ratio.  We suggest investigating how much your page file is required based on your regular application and resource demands.  For systems using a swapfile you will need to refer to the System Monitor and view peak values of the swapfile in use graph.  Follow this link for more information: http://www.techarp.com/showarticle.aspx?artno=143&pgno=23

For Windows XP, you will need to use the Task Manager and refer to the PF Usage graph. Accessing the Task Manager in XP is rather easy.  Try one of these options:

-          Combine the following keys: Ctrl + Shift + Esc.

-          Right-click in an empty space in the desktop taskbar and select: Task Manager. 

With Windows NT, 2000, XP, or Vista you can do the following:

1. Press: Ctrl + Alt + Delete.
2. Click the Task Manager button in the dialog that appears.

Now that you have the task manager open you can get a first hand view of your page file in action.  To view the PF Usage graph, click the Performance tab in the Windows Task Manager. 

Initial and Maximum Settings

So now that you know how to use the Task Manager you can adjust the page fault limits and compare the PF Usage.  If you were to set the same values for the Initial and Maximum values, the page file would be set as a permanent paging file.  By setting these values you have created what is known as a semi-permanent page file system.  The Initial size (minimum value) determines the size that the operating system first starts the page file (the permanent portion).  If the system requires it, the page file will be expanded dynamically to include a size up to and including the Maximum size set. 

The dynamic portion is used when required and is prone to defragmentation.  A defragmented page file, by some accounts, results in greater seek times and a resulting performance drop.  While there are those that recommend that you use a permanent page file solution, contrasting opinion provides a valid point: the page file is likely not read or written in sequential order.  If you are particularly motivated, you could create a contiguous and permanent page file with Windows XP by first defragmenting your hard disk and then setting the two values to the same level.

If your system uses more memory than what is provided for with available RAM, then you may want to consider occasionally defragmenting the page file.  There are applications available for this but we recommend other solutions as described below.  You might also want to have the Initial size set high enough to accommodate all your required needs so that the dynamic portion is only used as needed in extreme situations.  You may ask why not use a huge page file?  By creating a file that is excessive in size you will be taking up hard disk space that your system could be using.

Save and Reboot

If you are not certain you want to use the settings and want to return to the previous settings, you can click the Cancel button.  When you do want to save the settings you can click OK and a message appears asking you to restart the computer for the changes to take effect.  Close all your applications and reboot your system. 

Other Considerations

While adjusting the page file to an optimal level is beneficial, it does by its very use, result in some degradation of performance.  It should not be used if what is really required is to add more RAM.  Your system’s memory requirements are based on the types and numbers of programs you are running.  You can get a good indication of system performance from the Task Manager.  Optimizing the size of the page file can provide you with the ability to run several applications at once and will be useful when using applications that are resource “hogs” provided you have sufficient RAM to begin with.

Another consideration is to examine all the resources that are being used.  Often times there are programs that are running in the background or are automatically launched when you start your computer.  There are software programs that install to your system and are launched automatically by default.  Some of these can be more than a challenge to detect and to uninstall or remove.  We recommend using a utility program such as RegCure that has a startup program manager and can also work to clean up unwanted items in your registry.  To remove unwanted software items that can be malicious in nature – malware items – we suggest RegCure.  By providing yourself with the right tools you can protect yourself from offending programs that attempt to take control of your system.

In Conclusion

While understanding the purpose of a page file and how it works in a virtual memory management system is something each of us can realize even with the information presented here, it takes effort to determine how best to use it.  While there is so much available data it can feel as though your head is spinning faster than a data platter, it is best in the end to diagnose how your system is performing and what it requires.  You need to meet your system needs through a combination of tweaking the page file, using sufficient RAM, and taking control of the programs that are running at any one time.  With adjustments to page files – it is best to gage what your system needs using the Task Manager and running all the usual applications you normally would and then try different settings.  It may take time but you can feel confident that you have arrived at an optimal page file and virtual memory level of performance.