Why are Translation Look-aside Buffers (TLBs) important? In a simple paging system, what information is stored in a typical TLB table entry?

The implementation of page-table is done in the following way:
  • Page table is kept in main memory.
  • Page-table base register (PTBR) points to the page table.
  • Page-table length register (PRLR) indicates size of the page table.

One for the page table and one for the data/instruction.
The two-memory access problem can be solved by the use of a special fast-lookup hardware cache called
associative memory or translation look-aside buffers (TLBs). A set of associative registers is built of high-speed memory where each register consists of two parts: a key and a value. When the associative registers are presented with an item, it is compared with all keys simultaneously. If the item is found, the corresponding value field is the output.

A typical TLB table entry consists of page# and frame#, when a logical address is generated by the CPU, its page number is presented to a set of associative registers that contain page number along with their corresponding frame numbers. If the page number is found in the associative registers, its frame number is available and is used to access memory. If the page number is not in the associated registers, a memory reference to the page table must be made. When the frame number is obtained, it can be used to access memory and the page number along with its frame number is added to the associated registers.


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