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  Windows XP Memory Tweak Guide

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Registry Options

The System Registry contains several settings which allow you to further configure memory management features in Windows XP. Used properly this can further improve your PCs memory subsystemís performance. To access these click on Start, Run. Type in regedit and click Ok.

Navigate to [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SessionManager\Memory Management].

The options we are interested in are in the right hand pane. To edit any entry simply double click on it or right click on the entry and select Modify. In the parenthesis Iíll cover which format the Data is to be changed in. The more relevant options are as follows:

ClearPageFileAtShutdown. (Hexadecimal or Decimal). This setting allows inactive Pages in the Paging File to be cleared (Wrote with 0s) during shutdown. Itís certainly worth considering if youíre highly security conscious. When set to 0 (Default) inactive Pages are not written with 0s; having no effect on shutdown time and making Page File data readable (this is recommended and certainly safe for home users). A value of 1 enables inactive Pages to be cleared during shutdown, which is useful from a security viewpoint, although shutdown times will be increased; this is more appropriate in a business environment.

DisablePagingExecutive. (Hexadecimal or Decimal). This setting controls how inactive kernel-mode Drivers and system code are handled by the memory subsystem. A value of 0 (Default) specifies that inactive kernel-mode Drivers and system code can be released from RAM and paged to the Page File, this is perfectly fine on systems with lower amounts of RAM installed and with 512MB or less is recommended. A value of 1 specifies that inactive kernel-mode Drivers and system code are held in RAM; this provides enhanced performance on systems with a large amount of RAM as such data can be accessed significantly faster when held in RAM than having to be read from the Page File. Given the higher system requirements of Applications nowadays (especially games) you should only consider using this with greater than 512MB RAM installed.

IoPageLockLimit. This setting specifies the limit of the number of bytes that can be locked for I/O operations. Depending on the version of XP you have installed (Gold, Service Pack 1 or 2) this option may not appear. Regardless of whether itís listed or not itís an obsolete option which has no effect. While some suggest you may set this manually regardless, itís completely unnecessary. Donít adjust this value if itís listed, and certainly donít create an entry for it if itís not.

LargeSystemCache. (Hexadecimal or Decimal). This setting controls the size of the file system cache. When set to 0 (Default) a standard sized file system cache is allocated (Less than 10MB RAM); this is recommended as it provides best Application performance. When set to 1 this enables the use of a large file system cache (Up to RAM minus 4MB!); this option is only suitable when Windows XP is acting as a Server not as a gaming system or for other Application/Workstation use as it will be detrimental to performance as Microsoft notes:

When you enable System cache mode on a computer that uses Unified Memory Architecture-based video hardware or AGP, you may experience a severe and random decrease in performance. The Drivers for these components consume a large part of the remaining application memory when they are initialized during startup.

Further details can be found at the Microsoft KB.

Note Ė This is the same as the Memory usage option in the Performance Options, Advanced tab.

PagingFiles. This option specifies the location, file name and size of the Page File(s) for the system, for example:

C:\pagefile.sys 3 3

D:\pagefile.sys 450 750

Note Ė This is the similar to the Virtual Memory options window, accessible in the Performance Options, Advanced tab, pressing the Change button. The main point of potential interest with this option is that it allows you to rename the Page File, which might be of interest to a few people out there.

SecondLevelDataCache. This setting specifies the L2 Cache size of your CPU (Defaulting to 256K when unable to determine) and itís only appropriate to specify a value with CPUs with off-die L2 Cache (i.e. Pre-Pentium 2, in which case - update your hardware!). With any remotely modern CPU Windows accurately queries this value via the Hardware Abstraction Layer and as such thereís no need to adjust this option. While some suggest you may set this manually regardless; itís completely unnecessary. Leave this set to 0.

Other options listed, e.g. NonPagedPoolSize, can be ignored and are likely at their default of 0; indicating they are calculated automatically based on system configuration, e.g. RAM installed.

Now navigate to the PrefetchParameters subfolder ([HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PrefetchParameters]).

EnablePrefetcher. Prefetching is the process of tracing and recording page faults during boot/Application loads. This info is used subsequently to prefetch pages from disk to avoid page faults during boot. As device drivers are loaded, services started, and so on, then pages will be needed from the disk drive. Prefetching these pages means reading ahead before the pages are needed so that they are already in memory thereby eliminating disk I/O delays; providing improved boot/Application startup times. This is further enhanced by auto-defragmentation which moves this layout data to a contiguous (unfragmented) block. Prefetching is monitored continually, so the layout changes as your usage pattern does. This setting determines how XPís Prefetching feature functions. 4 options are available:

0. Selecting this option sets that Prefetching is disabled. This makes XP function similar to earlier versions of Windows when booting/launching Applications, i.e. itís slower. Thereís no particularly good reason to select this.

1. Selecting this option enables prefetching of Applications only. During system boot only pages relating to Applications will be fetched. This isnít particularly recommended as it increases boot time for no real reason.

2. Selecting this option enables boot prefetching. During system boot only pages relating to booting up are fetched, reducing boot times, although launches of regularly used Applications after startup make take longer unnecessarily. This is of some use when the system is acting as a Server as Applications wonít be a concern.

3. Selecting this option enables boot and Application prefetching. During system boot pages relating to both boot and Applications are fetched, which provides improved boot times and faster Application initialisations. This is highly recommended.

Some have suggested setting this to other values; such as 5. This is pointless however; they arenít even valid values, only 0-3 are. Further technical info on Prefetching can be found at Microsoft here and here.

Note Ė The Task Scheduler service needs to be set to Automatic for Prefetching to function correctly. Additionally there is no need to periodically clear the Prefetch directory for the reasons stated above, while using the /Prefetch command for launching Applications has no beneficial affect either.

EnableSuperfetch. This setting appeared thanks to an article by The Inquirer, claiming it provided XP with Windows Vista like performance. Unsurprisingly enough, itís not even a supported setting in XP and if you happened to create this entry right click and Delete it.

Now navigate to the SubSystems subfolder ([HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\SubSystems]). Itís been recommended to remove support for POSIX (Portable Operating System Interface), as it yields a negligible reduction in memory requirements. However, this is not necessary as POSIX Support isnít available by default in Windows XP.

Now navigate to [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer]. There may be a sub-key listed in the left hand pane entitled AlwaysUnloadDLL, with (Default) set to 1 in the right hand pane. Some recommend setting this as it frees unused DLLs (Dynamic Link Library) from memory quicker. This actually only applies to Windows Explorer extensions (As the Registry location hints) and as Microsoft notes:

The Shell automatically unloads a DLL when its usage count is zero, but only after the DLL has not been used for a period of time. This inactive period might be unacceptably long at times, especially when a Shell extension DLL is being debugged. For operating systems prior to Windows 2000, you can shorten the inactive period by adding the following information to the registry.

Essentially, if youíve got this sub-key listed right click on it (AlwaysUnloadDLL) and Delete it; itís completely unnecessary.

Restart your system for changes to take effect.



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