2. Paging
Paging is a memory-management schemes that permits the
physical address space of a process to be noncontiguous.
Physical memory is broken into fixed –sized blocks called
frames. Logical memory is broken into blocks of same size
called pages.
The page size and the frame size must be same.
When a process is to be executed, its pages are loaded into any
available memory frames from the backing store.
Every address generated by CPU is divided into two parts: a
page number (p) and a page offset/displacement(d).
The page table contains the base address of each page in
physical memory. This base address is combined with the page
offset to define the physical address.
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7. • Hardware Support
Each operating system has its own method of storing page
tables.
The page table is implemented as a set of dedicated registers.
TLB is associative,high-speed memory.Each entry in the TLB
consists of two parts,key and value.
The TLB contains only a few of the page-table entries.When a
logical address is generated by the CPU,its page number is
presented to the TLB.
If a page number is found in TLB- TLB hit
If a page number is not in TLB-TLB miss
The percentage of times that a particular page is found in the
TLB is called the hit ratio.
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9. • Protection
Memory protection in a paged environment is accomplished
by protection bits that are associated with each frame.
One more bit is generally attached to each entry in the page
table:a valid or invalid bit.
When this bit is set to valid ,this value indicates that the
associated page is in the process logical address space.
When this bit is set to invalid ,this value indicates that the
associated page is not in the process logical address space.
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