Computer Sciences > GATE 2025 SET-1 > Memory Management
Consider a demand paging memory management system with 32-bit logical address, 20-bit physical address, and page size of 2048 bytes. Assuming that the memory is byte addressable, what is the maximum number of entries in the page table?
A
221
B
220
C
222
D
224

Correct : b

Explanation:
1. Identify Given Parameters:
• Logical Address Space (LAS) size = 32 bits
• Page Size = 2048 bytes = 211 bytes (since 211 = 2048)

2. Understand Page Table Entries:
The number of entries in a page table is determined by the total number of pages in the Logical Address Space. Each page requires exactly one entry in the page table.

3. Calculate Page Offset:
Since the memory is byte-addressable and the page size is 211 bytes, the number of bits required for the page offset (offset within a page) is 11 bits.

4. Calculate Number of Page Bits:
The logical address is split into two parts: Page Number bits and Page Offset bits.
• Logical Address (32 bits) = Page Number bits + Page Offset bits (11 bits)
• Page Number bits = 32 - 11 = 21 bits

5. Calculate Maximum Number of Entries:
With 21 bits allocated for the page number, the maximum number of unique pages (and therefore the maximum number of entries in the page table) is:
    221

Note: If option (a) was meant to represent 221, then option (a) is the correct choice. Written as plain integers, 221 is the exact capacity.

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