Page Fault Definition Explained
A page fault occurs when a program attempts to access data or code residing in a specific page of virtual memory, but that page is not currently loaded into the physical memory (RAM).
Triggering a Page Fault
The fundamental reason for a page fault is accessing a required page that is absent from main memory. This triggers an exception handled by the Operating System (OS).
Steps in Page Fault Handling
- Program access attempt targets a page not in RAM.
- The Memory Management Unit (MMU) detects the missing page and generates an exception.
- The OS's page fault handler takes control.
- The OS finds the required page on secondary storage (disk).
- A free frame in RAM is allocated, or if necessary, an existing page is swapped out.
- The required page is loaded from disk into the allocated RAM frame.
- The process's page table is updated to map the virtual page to the physical frame.
- The instruction that caused the fault is re-executed successfully.
Why Option 2 is Correct
Option 2 correctly states that a page fault occurs "when a page currently not in a memory is accessed". This is the precise definition. The system needs the page, checks memory, finds it missing, and thus generates the fault.
Why Other Options Are Incorrect
- Option 1 describes normal memory access, not an error condition.
- Options 3 and 4 relate to page replacement, which is a *consequence* or *related process* managed by the OS during fault handling, not the direct cause of the fault itself. The fault happens because the page is *needed* and *missing*, irrespective of whether it might eventually be involved in a replacement operation.
Important Questions from Memory Management
Which of the following is the main function of the memory management system?
1. It keeps track of which parts of the memory are currently in use.
II. When memory is available, it allocates memory to the programs to be loaded.
How many address lines and input-output data lines are needed in a 2k × 16 memory unit?
Suppose you have eight 'black and white' images taken with a 1‐megapixel camera and one '8‐color' image taken by an 8‐megapixel camera. How much hard disk space in total do you need to store these images on your computer?
Computational circuitry in a CPU is referred to as the ____________
Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: Major advantage of DRAM is that the capacitor cell never loses its charge and hence there is no need to refresh periodically.
Reason R: When DRAM is being refreshed, the data cannot be accessed.
In light of the above statements, choose the correct answer from the options given below
