Quiz submission record for quiz7-1-1 at Mon Aug  2 00:39:12 2004:

Your Answer for Question 1:
Virtual memory helps manage the two levels of memory hierarchy represented by main memory and secondary storage (magnetic disks). The CPU produces a virtual address (VA), which is translated by a combination of hardware and software to a physical address (PA), which is then used to access main memory. Essentially, in virtual memory, blocks of memory (pages) are mapped from virtual addresses to physical addresses. Each virtual address is mapped to a physical address. However, it can be possible for a virtual address not to be mapped and only reside on the disk. Physical pages can be shared by having two virtual addresses point to the same physical address. This allows different programs to share the same data/code. 

Each virtual address is broken into a virtual page number and a page offset. The physical address, which does not need to match the # of addressable pages as the virtual address, also has two parts. The page offset stays constant in both and resides in the lower portion of the address. The virtual page number then translates into a physical page number and resides in the upper portion of both the virtual and physical address. 


Your Answer for Question 2:
By having the VM system allocate pages in fixed-size chunks eliminates the need to find a contiguous block of memory to allocate to any program. The OS need only find a sufficient number of pages in main memory. The benefit of allocating pages in smaller chunks or of variable-size is to support more powerful methods of protection and sharing in an address space. 


Your unique submission ID is quiz7-1-1-cs61c-ei-1091432352-2280.