Virtual Memory

This article addresses virtual memory and related issues.  The purpose is to provide clear descriptions and recommendations.  As this is a complex computer function, we suggest that you continue to do more investigation if coming across areas that are of interest to you.  We have provided some useful links to point you in the right direction.

A Definition

In simple terms, virtual memory is a particular method of temporarily storing information used by most desktop operating systems.  To go a little deeper than this we will need to provide a few definitions of some frequently used terms.

-    Memory: computer memory is related to storage of information; this can be physical memory stored on a physical storage device or it can be virtual memory.

-    Main memory: the actual physical memory used by a computer that is internal to the system (such as RAM).  The term main is used to set it apart from external storage of data such as disk drives.  As will be described in this article, the amount of memory that is in main memory directly impacts the amount of applications that can be running at one time.

-    RAM: Random Access Memory (RAM) is memory that is stored on a physical device – a chip or module.  It is “volatile” in that it is not permanently stored.  Instead it becomes lost when the computer is turned off.  It is also referred to as read-write memory.

-   Address: like a street address, computers use addresses for managing and locating data in memory. Each address is a unique number utilized by programs and the operating system.

-   Page: a specific area for data storage, or computer instructions, or a combination of these.  The operating system creates pages for virtual memory and each contains a fixed range of addresses.

-   Paging: the act of transferring data, instructions, or a combination of both of these, between the hard disk drive and memory.  This is also called “swapping”.

-  Mapping: the translation of virtual addresses to real physical addresses.

-   Processes: when an application runs it will use one or more tasks that are required to carry out the program’s instructions.

Virtual memory is useful as it enables access to a larger range of memory than what could be provided by main memory alone.  The operating system maps virtual addresses between software programs and actual storage addresses in physical memory.  Virtual memory is also frequently used in the swapping of storage between RAM and physical storage devices (such as your physical hard disk drive or external drives).  In an effort to run several applications at the same time, your computer will free up areas in RAM that have not been recently used by copying data to the hard disk.

So, in a nutshell, the operating system utilizes a virtual memory technique whereby it creates pages that have specific addresses so that data can be stored until required for use.  When the data is required a paging process occurs where data is copied from the physical disk storage to main memory. 

Since Windows 3.0 was introduced (as early as 1990), virtual memory was used in Microsoft Windows systems.  A virtual memory “swapfile”, called WIN386.SWP (or 386SPART.PAR), was created and by default was hidden from user.  Certain system files like this are called “hidden files” and can be viewed if you change the setting in Windows Explorer.  With the introduction of Windows 95, the file was no longer referred to as a swapfile but as a paging file.  It can be accessed and configured by going to the virtual memory section of the System settings (Control Panel | System | Performance tab). 

With the onset of NT systems such as Windows 2000 and Windows XP, paging files came into existence.  The file is called: “pagefile.sys” and is located by default in the directory where Windows was installed.  Like its predecessor it is used to create virtual memory.  Where swapfiles move entire processes to system memory, paging files move “pages” to a page file.  The use of swapfiles occurs when there is a significant resource demand on the system.  One other distinction between these two – the use of swapfiles is based on heavy resource demand where paging can be pre-emptive. 

Not So Virtual Issues

While virtual memory is advantageous in terms of making use of available storage and utilizing the fastest memory on your system, there are known instances of errors occurring.  The most common of these involves page faults.  Page fault errors are also known as invalid page faults and there are various conditions that cause these.  The most common subset of these is referred to as a general protection fault.  They are typically caused by instability with virtual memory due to shortages of either free disk space or RAM.

Other page faults involve issues related to applications.  For example:

-          A program attempts to access data that is in use by another active program.

-          Virtual memory becomes corrupt as a result of a program not behaving as expected.

When a page fault is encountered the operating system attempts to solve the problem and, if it succeeds, a paging operation (“swapping”) takes place – it transfers control to the program.  If it does not succeed, an error message will appear.  If this is the case you can go to the Microsoft support site and enter the type of error message to see if it is listed there.  To search the support site do the following:

1. Click on this link or type it in your Internet Browser: http://support.microsoft.com/search/
2. In the Search Product field, click the drop down arrow and select your operating system or a particular application you suspect as a possible cause.
3. In the For field, type the name of the page fault error.
4. Click Search.

Thrashing

As mentioned, data is transferred from storage spaces such as the physical disk drive to main memory (RAM).  One of the reasons for this is that RAM memory is faster than hard disk drives.  Disk drives are not designed to deal with small pieces of data.  However, if your system has too large a reliance on virtual memory, you can expect a decrease in performance especially when many programs and processes are running consecutively.  You can typically detect this when switching form one program task to another.  If there are delays the operating system is swapping information from the hard disk to RAM memory.  When the hard disk drive is used excessively as a virtual memory resource, your computer may experience what is commonly known as “thrashing”.

You can tell if your system is thrashing if an open application no longer responds but the hard disk drive light is blinking off and on.  Other symptoms include noise being made by the computer.  This brings about an over-reliance on system functions that require electricity and will result in a faster decrease of battery life for laptops.  In these situations, the running processes are competing for resources.  In order to temporarily remedy the situation you need to close programs that are not in use.  To fix the problem you will need to try one or more strategies.

-          Add more RAM.

-          Kill startup programs from running in the background (see below for more information).

Causes for Concern… and Solutions

Your overall system performance can be affected by how well your virtual memory is able to function and how well it is managed.  In some instances this may mean that you have to “tweak” or fine-tune the settings.  Before doing this it is best that you do some initial research and have a clear idea of what adjustments you are going to use beforehand. 

If you are running Windows 98 we recommend visiting the following site which has considerable information on virtual memory and how to configure it for best performance: http://computer.howstuffworks.com/virtual-memory.htm.  It appears that this article was not written recently – it states that today’s computers have 32 to 64 megabytes (MB) of RAM.  However, it is applicable to Windows 98 systems and you will find detailed information on how to configure virtual memory (use the “Inside This Article” links at the top of the page for easy navigation).

For more recent systems it is clear that today’s demand on computers is greater than in the past and the addition of RAM is commonplace.  Even with 256 MB of RAM or more, your computer system still requires paging and virtual memory techniques.  Software programs rely on paging to store sensitive data rather than having to rely on “volatile” (temporary) storage such as RAM.  Also, it is common to run several programs as we often multi-task while working on a computer.  It’s not unusual to have an instant messenger program running in the background, while an email program is running, while a word document is open, while listening to music from your computer system. 

To get a better idea of what is running on your system at any one time you can use Windows Task Manager.  You can access the task manager by combining the following keys: Ctrl + Shift + Esc.  You can also right-click an empty space in the taskbar and select the Task Manager option.  If you are running Windows 2000, NT, XP, or Vista you can try the following:

1. Press and hold the following keys in sequence: Ctrl + Alt + Delete.
2. Your screen will change and a dialog with six options will appear; click the Task Manager button.

The Task Manager has many functions including setting priorities for processes, logging off or disconnecting users, and ending tasks or processes.  While these functions are available to you, you need to use caution when ending a process or application.  This is not the usual way to close applications and as a result data is not saved.  We recommend that you only use this option when you know what the process is and other attempts have failed.  Once you have opened the Task Manager you can select any of the tabs displayed at the top of the dialog.  The Applications tab will list all the active programs that are running.  The Processes tab provides a lot of information about the active tasks that are running including “Mem Usage”.  The Performance tab will give you an idea of how heavily tasked your CPU is and give you a clear indication of your Page File Usage, the total amount of Physical Memory on your system and what is cached and what is available. 

Experts tend to lean to one solution when insufficient memory is encountered – add more RAM.  Another technique involves changing your settings in an attempt to achieve performance optimization.  While you can choose to optimize your page file, you should know that it will not improve performance.  Instead it will minimize system slow down when you are using programs that place heavy demands on your system or when multi-tasking.  To examine methods of page file optimization we suggest referring to information presented in the following article: http://www.techarp.com/showarticle.aspx?artno=143&pgno=3.  You can use the quick link menu at the bottom of the page to see a list of topics and to link to one of your choice.  In these articles you can find out how to configure your page file to make it permanent or semi-permanent and how to ensure that it is contiguous.

If, like most computer users today, you are doing a considerable amount of online browsing and you have done a numerous software installations and un-installations, your system could be prone to slow performance.  When traversing the Internet, files are automatically downloaded to your system.  Most of these are only meant for temporary use.  Over time a large number of downloaded items can clog up your hard disk drive and your computer registry.  Another common occurrence that affects performance is when applications automatically install by default to your Startup list (Start | Programs | Startup).  This has considerable impact on how quick your computer starts as these programs and processes are initiated each time you start your computer.  We recommend using a program that can clean up unwanted and unused items from your registry and also gives you the ability to decide what programs are launched when you start your computer. 

Malicious Software Attacks

With the virtual memory system there is a process referred to as “memory protection”.  This involves protecting the memory allocated for a running process so that other processes do not access it without permission.  Malfunctioning code in one program can cause problems with other running programs if this protection mechanism is violated.  There are situations where malicious code can be the cause of such violations as the offending program gains access to your computer system.

The Windows Task Manager is commonly targeted and sabotaged by malware (malicious software) and virus programs.  In an attempt to evade termination and detection, malware will try to disable the manager program, modify the Task Manager’s registry policy settings, or alter the Task Manager so as to go unnoticed.

Defending yourself from such attacks is crucial as is being able to remove these offenders from your system when they are installed without your knowledge.  Malware, also commonly known as “spyware”, can be downloaded to your system without your knowledge simply by browsing to a web site.  These programs can tax your system resources.  Many of these are adware programs that produce popup advertisements and become more than an annoyance when attempting to remove them.  The first line of defence in such situations is to use a software program that can detect the items and remove them completely.  Your choice for an anti-spyware product should be based on having ongoing updates so as to get the most recent and up-to-date protection from these threats.  We recommend XoftSpySe Anti-Spyware.