•OS code has its own virtual address range
•If OS has the same virtual address range (0 – 0xFFFFFFFF) than every system call has to trigger the change in virtual to physical mapping (very expensive procedure)
•MSFT has decided to allocate upper 2Gb of virtual address space to OS code (0x80000000 – 0xFFFFFFFF) – default configuration
•To support application that require more virtual addresses (for example, DB applications) you can specify /3GB switch in boot.ini
•Now every OS call does not require change in mapping because mapping for virtual addreses 0x80000000 – 0xFFFFFFFF is the same for every process