GATE CS 2024 Set 2 — Question 24

MSQ+1 / -0MediumPaging & Address TranslationMemory ManagementOperating System

Operating System → Memory Management → Paging & Address Translation

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Question

Which of the following tasks is/are the responsibility/responsibilities of the memory management unit (MMU) in a system with paging-based memory management?
A.
Allocate a new page table for a newly created process
B.
Translate a virtual address to a physical address using the page table
C.
Raise a trap when a virtual address is not found in the page table
D.
Raise a trap when a process tries to write to a page marked with read-only permission in the page table

Correct answer

(B) Translate a virtual address to a physical address using the page table; (C) Raise a trap when a virtual address is not found in the page table; (D) Raise a trap when a process tries to write to a page marked with read-only permission in the page table

Solution

The Memory Management Unit (MMU) is a hardware component responsible for handling memory accesses requested by the CPU.
(A) False: Allocating a new page table is a memory management task performed by the Operating System kernel when a process is created. The MMU uses the page table but does not create/allocate it.
(B) True: The primary function of the MMU is to translate virtual addresses to physical addresses at runtime using the page table (and TLB).
(C) True: If a translation is not present (valid bit is 0) in the page table (or TLB), the MMU raises a hardware exception (trap), commonly known as a page fault, so the OS can handle it.
(D) True: The MMU checks access permissions (Read/Write/Execute bits) present in the page table entries. If a process attempts an operation that violates these permissions (e.g., writing to a read-only page), the MMU raises a protection fault/trap.

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