http://kadaitcha.ath.cx/articles/performance.aspx
Tweak #5: Memory Management and Processor Scheduling
256MB RAM is the absolute minimum to take advantage of these changes. Those with faster Pentium 4's should see a significant performance boost. You should not perform any registry edits unless you know what you are doing. At the very least, you should consider performing a backup before proceeding.
Memory Management: Kernel Paging and Cache Tuning
The "DisablePagingExecutive" entry in the registry prevents the kernel (the core of the XP OS) from being rolled out to the page file. The effect of this part of the tweak is to cause the OS to cache the OS Kernel and its entourage to RAM instead of to disk, which makes XP far more responsive.
The "LargeSystemCache" registry entry forces XP to allocate all but 4MB of system memory, that is system memory, not avaliable RAM, to the file system cache. The remaining 4MB of system memory is used for disk caching, though XP will allocate more memory if it is needed.
A modern hard disk will transfer sequential data to and from disk at up to 40MB per second, or even faster on some 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 data read from disk in RAM. It means that the OS 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, 200MB or more of RAM in a typical 512MB machine 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 either SQL Server or Internet Information Server (IIS) because both of those applications perform their own caching.
Start regedit and navigate to the following key:
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management]
Add these two lines, save the changes and reboot;
"DisablePagingExecutive"=dword:00000001
"LargeSystemCache"=dword:00000001
To see the effects of this part of the tweak, launch a large, memory hungry application. Any of the Microsoft Office suite of applications will do. Let the application load then exit from it. Fasten your safety harness then launch the application again.
I have a striped RAID 0 array of two ATA100 7,200 RPM disks. The array was lounging around on holiday in the sun and not doing much with a SiSoft Sandra Drive Index of 28,000. The two registry changes above caused the DI to triple from the original 28,000 to an upper mark of 85,000. A similar but scaled down performance increase can be expected for ATA 33/66 disks.