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Translation Look-aside Buffers

• using multi-level page table can save space.
• example: for 32-bit virtual address, 1 GB physical memory, and 4 kB pages how many bits do we need for the frame number? 1GB = 30 physical address bits. 4KB is 12 offset bits. Thus we need 30-12 = 18 bits for the frame number.
• but this multi-level can also be very expensive, because we need to lookup that many times
• potential solution: cache this! called translation look-aside buffers.
• Similar to Cache Average Access Time,
$T_\text{Translation} = T_\text{TLB Lookup} + (1 - P_\text{TLB Hit}) \times T_\text{Page Table Walk}$