Question

Which one of the following statements is FALSE?

• A. The TLB performs an associative search in parallel on all its valid entries using page number of incoming virtual address.
• B. If the virtual address of a word given by CPU has a TLB hit, but the subsequent search for the word results in a cache miss, then the word will always be present in the main memory.
• C. The memory access time using a given inverted page table is always the same for all incoming virtual addresses.
• D. In a system that uses hashed page tables, if two distinct virtual addresses V1 and V2 map to the same value while hashing, then the memory access time of these addresses will not be the same.

Hint:

Inverted page tables and hashing can introduce non-uniform memory access times, especially when collisions occur in hashed page tables.

Answer 1

The Correct Option is C

- Option (A): The TLB (Translation Lookaside Buffer) performs an associative search on its valid entries to speed up the translation of virtual addresses to physical addresses. This is a true statement, as the TLB indeed operates by searching all its entries in parallel. - Option (B): If there is a TLB hit for a given address but later a cache miss occurs, this implies the cache was not able to find the corresponding data. However, the word will still be present in main memory, as the memory management unit ensures that data is eventually fetched from there. This is a true statement. - Option (C): Inverted page tables work by using a hash function or an indexed lookup to convert virtual addresses. The time taken to perform lookups might differ depending on the actual address and lookup structure. Hence, the statement that the access time is always the same for all incoming virtual addresses is false. - Option (D): In systems using hashed page tables, when two different virtual addresses map to the same hash value (a collision), the memory access time for those addresses can differ because collision resolution mechanisms like chaining or open addressing are used, resulting in additional time for lookup. This is a true statement. Final Answer: (C)