Reblogged from TTC Shelbyville - Technical Blog:
32bit processors and operating systems have a limitation of 3GB. Programs are limited to 2GB of RAM. These tweaks increase the OS's ability to recognize more RAM and increase the ceiling for programs that can recognize more than 2GB of RAM. (Above 3 GB, all memory may not be available due to system resource requirements. The memory above 3 GB is used for PCI I/O and other system resources.