| Translation Lookaside Buffer |
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Information AboutTranslation Lookaside Buffer |
| CATEGORIES ABOUT TRANSLATION LOOKASIDE BUFFER | |
| virtual memory | |
| computer memory | |
| central processing unit | |
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OVERVIEW The TLB references physical memory addresses in its table. It may reside between the CPU and the CPU Cache or between the CPU cache and Primary Storage memory. This depends on whether the cache uses physical or virtual addressing. If the cache is virtually addressed, requests are sent directly from the CPU to the cache, which then accesses the TLB as necessary. If the cache is physically addressed, the CPU does a TLB lookup on every memory operation, and the resulting physical address is sent to the cache. There are pros and cons to both implementations. A common optimization for physically addressed caches is to perform the TLB lookup in parallel with the cache access. The low-order bits of any virtual address (e.g., in a section in the cache article for more details about virtual addressing as it pertains to caches and TLBs. MISS Two schemes for handling TLB misses are commonly found in modern architectures:
TYPICAL STATISTICS :Size: 8 - 4,096 entries :Hit time: 0.5 - 1 clock cycle :Miss penalty: 10 - 30 clock cycles :Miss rate: 0.01% - 1% If a TLB hit takes 1 clock cycle, a miss takes 30 clock cycles, and the miss rate is 1%, the effective memory cycle rate is an average of clock cycles per memory access. USAGE All current x86 processors use a TLB. In some newer processors it is even possible to share a single entry between different processors even if their access rights differ. This practice improves RAM access times. SEE ALSO |
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