NIMCET 2024 — Computer PYQ

1. Analyze the Virtual Address

• Total Virtual Address size: 32 bits

• Page Size: $4\text{ KB}=2^{12}\text{ bytes}$

• Page Offset: Since the page size is $2^{12}$, the offset requires 12 bits.

• Virtual Page Number (VPN):

  $$\text{VPN bits}=\text{Total Virtual Address bits}-\text{Page Offset bits}$$
  $$\text{VPN bits}=32-12=20\text{ bits}$$

2. Analyze the TLB Structure

The TLB acts like a cache for the page table. Since it is 4-way set associative, we need to find how many sets exist to determine the Index bits.

• Total TLB entries: 128

• Associativity: 4-way (4 entries per set)

• Number of Sets:

  $$\text{Number of Sets}=\frac{\text{Total Entries}}{\text{Associativity}}=\frac{128}{4}=32\text{ sets}$$

• TLB Index bits: Since there are $32$ sets ($2^5$), we need 5 bits for the index.

3. Calculate the TLB Tag Size

The Virtual Page Number (VPN) is divided into the TLB Tag and the TLB Index.

Final Answer

The minimum size of the TLB tag is 15 bits.

Correct Option: (C) 15 bits