CGS 3763 Operating Systems Concepts Spring 2013 Dan C. Marinescu Office: HEC 304 Office hours: M-Wd 11: :30 AM

Last time: Paging  Today Problem solving – Dynamic Address Translation  Next time  Virtual memory Reading assignments  Chapters 8 and 9 of the textbook Lecture 35 – Wednesday, April 10, 2013 Lecture 352

Dynamic Address Translation Address generated by CPU is divided into:  Page number (p) – used as an index into a page table which contains base address of each page in physical memory  Page offset (d) – combined with base address to define the physical memory address that is sent to the memory unit  A logical address consists of (m-n + n) =m bits. Thus the size of the logical address space is 2 m.  There are n bits to specify an address in a page thus the page size is 2 n page number page offset p d m - n n Lecture 353

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Example We assume a byte addressable memory. A virtual address is 32 bits  the maximum size of the virtual address space of a process is 2 32 = 4 GB. The page size is 4 KB  we need 12 bits to identify an address in a page (2 12 = 4 KB). The number of bits used to identify a page is 32 – 12 = 20. This means that the maximum number of pages thus the maximum size of the page table of a process is 2 20 = 1,000,000 entries. How do we translate the virtual address: to a physical/real address assuming that page 5 is in the main memory at address 1000? Lecture 355