Virtual Memory Organisation Questions and Answers

Answer: D

The memory is virtual memory.

Virtual memory gives each program an address space larger than physical memory. Pages are kept on disk and brought into main memory when referenced, with the page table mapping virtual to physical addresses, so a program can run even if it does not fit in RAM.

Auxiliary memory is the disk storage itself, associative memory is content-addressable memory used for lookups such as the TLB, and cache memory speeds up access but does not enlarge the address space.

Answer: C

The maximum TLB tag size is 15 bits.

Work out the virtual page number, then the bits used to index the TLB sets:

\[ \begin{aligned} \text{offset} &= \log_{2} 4096 = 12 \text{ bits} \\ \text{page number} &= 32 - 12 = 20 \text{ bits} \\ \text{sets} &= 128 / 4 = 32 = 2^{5} \\ \text{tag} &= 20 - 5 = 15 \text{ bits} \end{aligned} \]

20 bits would be the tag of a fully associative TLB, where the whole page number is compared. 11 and 13 bits come from subtracting the wrong number of index bits.

Answer: B

The TLB's purpose is to cache page table entries.

Translating a virtual address needs the page table, which lives in main memory. Reading it on every access would double the memory traffic. The TLB is a small, fast associative cache that holds recently used page-to-frame translations, so most translations take one quick lookup instead of a page table walk.

It does not store program data, which is the job of the data cache. It does not buffer I/O, and interrupt vectors are held in the interrupt vector table, not the TLB.