Normally, the tweak I've seen asks you to go into HKLM\System\CurrentControlSet\Control\SessionManager\Memory Management and change the value either O or 1 to the adjustment LargeSystemCache.
However, in Windows XP, all you have to do is:
· Right-click My Computer.
· Select Properties.
· Click Advanced.
· Choose Performance.
· Click Advanced again.
· Select either Programs or System Cache.
Programs = 0 for the registry tweak equivalent System Cache = 1 for the registry tweak equivalent
· On NT Server (in this case XP), the Large System Cache option is enabled, but disabled on Workstation The 2 different settings effect how the cache manager allocates free memory. If the Large Cache option is on, manager marks all the free memory, which isn't being used by the system and / or by applications, as freely available for disk caching.
· On the flip-side (with a small cache), the manager instead only sets aside four MB of memory for disk caching in an attempt to accelerate the launch of the
applications.Or in a more technical approach,if enabled the system will favor system-cache working sets over process working sets (with a working set basically being the memory used by components of a process).