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Memory Management and Virtual Memory

GATE CSE 2025 Set 2 · Q58

NAT2 marksMedium

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A computer system supports a logical address space of 2322^{32} bytes. It uses two-level hierarchical paging with a page size of 4096 bytes. A logical address is divided into a bb-bit index to the outer page table, an offset within the page of the inner page table, and an offset within the desired page. Each entry of the inner page table uses eight bytes. All the pages in the system have the same size. The value of bb is ____________ . (Answer in integer)

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Official answer: 11

Memory Management and Virtual Memory
  1. Logical Address Space Size:

    Logical Address Space=232 bytes  ⟹  Logical Address=32 bits\text{Logical Address Space} = 2^{32} \text{ bytes} \implies \text{Logical Address} = 32 \text{ bits}
  2. Page Offset (Offset within the desired page):

    Page Size=4096 bytes=212 bytes  ⟹  Page Offset=12 bits\text{Page Size} = 4096 \text{ bytes} = 2^{12} \text{ bytes} \implies \text{Page Offset} = 12 \text{ bits}
  3. Offset within the Page of the Inner Page Table: Since each page table must fit into a single page frame of size 4096 bytes4096\text{ bytes}:

    Number of entries per inner page table=Page SizeInner Page Table Entry Size=4096 bytes8 bytes=512=29\text{Number of entries per inner page table} = \frac{\text{Page Size}}{\text{Inner Page Table Entry Size}} = \frac{4096 \text{ bytes}}{8 \text{ bytes}} = 512 = 2^9

    Therefore, the number of bits required to index within an inner page table page is 9 bits9\text{ bits}.

  4. Outer Page Table Index (bb):

    Total Logical Address Bits=b+(inner page index bits)+(page offset bits)\text{Total Logical Address Bits} = b + (\text{inner page index bits}) + (\text{page offset bits})
    32=b+9+1232 = b + 9 + 12
    b=32−21=11b = 32 - 21 = 11

Thus, the value of bb is 11.

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This Memory Management and Virtual Memory previous year question is Q58 of the GATE CSE 2025 Set 2 paper. Find more GATE CSE PYQs on Memory Management and Virtual Memory in Operating Systems, or browse all GATE CSE PYQs.

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Memory Management and Virtual Memory in GATE CSE

Memory Management and Virtual Memory has 32 GATE CSE PYQs across 22 papers from 2011 to 2026. 15 of them are 2-mark NAT questions like this one, and GATE CSE 2025 Set 2 has 2.

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GateAI solution cardGATE CSE 2025 Set 2 · Q58 · NAT

A computer system supports a logical address space of 232 bytes. It uses two-level hierarchical paging with a page size of 4096 bytes. A logical address is divided into a b-bit index to the outer page table, an offset within the page of the inner page table, and an offset within the desired page. Each entry of the inner page table uses eight bytes. All the pages in the system have the same size. The value of b is … (Answer in integer)

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