x64? My Terminal Servers Run Just Fine With 32 Bits and 8/12/16 GB RAM! | sepago: "x64? My Terminal Servers Run Just Fine With 32 Bits and 8/12/16 GB RAM!
PAE
Windows can be booted with the /PAE option. PAE makes the kernel use 4 additional address lines which are built into (nearly) every CPU since the Pentium Pro. Modern CPUs have 36 instead of 32 address lines and support a maximum of 64 GB RAM (with PAE enabled).
But how can a traditional 32-bit application that can only count to 2^32 and that knows nothing of AWE access such "high" memory?
Easy: all the hard work is done by the operating system. Remember that each application has its private virtual address space that always ranges from 0x00000000 to 0xFFFFFFFF. But programs cannot simply access any address in that range. Doing so would result in the well-known general protection fault. Instead applications must request memory from the OS. The OS then chooses the appropriate amount of free pages (RAM is managed in units of pages with a size of 4 KB each). Finally the pages are mapped from physical RAM into the virtual memory of the requesting process.
By virtualizing the address space of processes, it has become irrelevant to applications where a page actually is located. It could have been moved to disk (to the page file, of course) to make room for other process's demands. Or it could reside in the area above 4 GB. Since applications only work with virtual addresses in the 32-bit range they need not be modified as long as they use less than 2 GB of memory.
With PAE, multiple 32-bit processes without AWE support can still only use 2 GB each. But it is perfectly possible to have 20 applications on a terminal server that each need 300 MB RAM if the machine is equipped with 8 GB (leaving room for the kernel and OS). This is because the map from virtual to physical memory is different for every process.
