Windows XP Performance Tweak

The "DisablePagingExecutive" entry in the registry prevents the kernel (ntoskrnl.exe, part of the core of the XP OS) from being rolled out to a pagefile on disk.

The effect of this first part of this tweak is to cause XP to cache the Kernel in RAM instead of on disk, which makes XP more responsive to requests to the core component functions that are performed by ntoskrnl.exe.

The "LargeSystemCache" registry entry forces XP to allocate up to all but 4MB of system memory, that is system memory, not available RAM, to the file system cache. The remaining system memory is used for disk caching, though XP will allocate more memory if it is needed. In rough terms, system memory is where XP holds programs and data that are currently in use. This allows applications and files to be cached in RAM rather than stored on disk.

A modern hard disk will transfer sequential data to and from disk at up to 40MB per second, or even faster on some of the more expensive, faster-spinning drives, but the LargeSystemCache tweak means that effective transfer speeds of 1GB per second or more can be obtained, depending on the amount of RAM in your system and its operating speed. This is achieved because the LargeSystemCache modification causes the OS to store applications in RAM after reading them from disk. Having a large system cache means that XP is always using the optimum amount of RAM instead of leaving it untouched for future use that may or may not occur. Without this part of the tweak, 256MB or more of RAM in a typical workstation goes completely unused.

Some I/O intensive applications may take a hit in performance from changing the LargeSystemCache, so this particular component of the tweak should not be applied to a system that is running very disk-intensive applications.

Part 1  DisablePagingExecutive:
Start RegEdit and navigate to the following key:
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management]
Double-click the DisablePagingExecutive entry and change the default value from 0 to 1

Part 2 Enable LargeSystemCache:
Repeat the previous step for LargeSystemCache, by changing the default value to 1.
Note that the LargeSystemCache entry is in the same registry block asthe entry for DisablePagingExecutive:
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management]

To see the effects of this tweak, reboot then launch a large, memory hungry application. Any of the Microsoft Office suite of applications will do that job nicely. Let the application load, then exit from it. Fasten your safety harness then launch the application again.

A PC with a striped RAID 0 array of two ATA100 7,200 RPM disks with a SiSoft Sandra Drive Index of 28,000 had the two registry changes above applied to it and the Drive Index tripled to an upper mark of 85,000. A similar, scaled-up performance increase can be expected for faster disks.

The more RAM you have, the better this tweak will perform. If you have more than 1GB (note, more than 1GB) then your system cache can expand up to its 32-bit limit of 1GB. If you have an x64 XP and if you are fortunate enough to be able to afford the RAM, your system cache can be expanded to one terabyte, which is a bit odd if you consider the maximum non-pooled RAM size (virtual addresses that are guaranteed to be resident in physical memory at all times and can be accessed without causing a page fault) is 128GB in an x64 edition of Windows.