Length of the virtual address in VAX-11 virtual memory is 32 bits

• Virtual address format: The higher order bit b31 differentiates between the user space and system space
• User space is further divided into program and control regions by bit b30
• The user program region contains program and data, and the user control region contains the user stack and operating system data structures pertinent to a particular user
• The system contains the routines of OS
• The remaining 30 bits of the virtual address specify a 21 bit virtual page number and a 9 bit address of a byte within that page
• Thus a page contains 512 bytes.
• During the address translation, the low order 9 bits of a virtual address are taken directly as the low order bits of the corresponding physical address
• Page is the basic unit that is transferred from secondary storage to the physical main memory
• The 21 bit virtual page number is used as an offset into a page table
• The address of the page table is held in a page table base register in the processor
• Each page table entry is 32 bits long and each entry contains a 21 bit physical page frame number used to construct a 30 bit physical address
• The remaining 11 bits of the page table entry provide access control information for the referenced page  

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