Owing to cheaper memory it is becoming increasingly common that modern PC's have >4GB physical memory. However because of the limitations of 32-bit IBM PC architecture, to access full 4GB RAM or more, the CPU processor must support Physical Address Extension (PAE), as well as the North-bridge Chip must have the Memory Remapping feature. Even the hardware has enabled these features, the operating system may still constrain the full use of the large memory.

It is possible however to access this additional memory installed using something called a "RamDisk". Normally when your physical memory is exceeded Windows will use a "pagefile" (located on a hard drive... access times on hard drives is much slower than RAM) to act as additional memory. It is possible however to use your additional memory as a pagefile, using some special tools.

Windows XP/ Vista: VSuite from Romex
Windows 9x/ Me: Link

These two above applications contain some special code that isn't normaly available in other "RamDisk" software.

You can also use the tools to setup things like your TEMP folder, browser cache etc to be located in your memory for even faster access!

64-Bit Windows doesn't have such a 4GB physical memory limitation.