Paging
A paging system divides main memory, physical memory, into blocks called frames. The size of a frame
is some power of 2 (for reasons that will become clear), and systems have implemented frames of sizes from
512 bytes to 64K. A typical size is 4K (1024 addresses in a system with a 32-bit, or 4-byte, word size).
A paging system divides logical memory into ???pages??? of the same size as the frames. When the operating
system needs to allocate memory to a process, it selects one or more empty frames, and maps the process pages
to the frames by means of a ???page table.???
The page table for a process has an entry for each page in the process??™ logical address space. When the
process requires access to memory, the system inspects the logical address to determine which page it references.
Then the system consults the page table entry for that logical page to learn what frame in physical memory the
process is referencing. Finally, the system executes the reference to the proper physical memory location in the
appropriate frame.
Making the frame and page size a power of 2 speeds the process, because it means that the logical address
can be conveniently split into two fields, a ???page number??? and an ???offset.
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