Virtual Memory and Page Faults
The concept of virtual memory is designed to enhance the efficiency of a computer system by allowing a process to execute even when only a portion of it is present in the main memory (RAM). This partial presence is managed through a mechanism called paging.
Key Points of Paging
- Partial Process in Main Memory:
- Only a part of a process needs to be in the main memory for execution.
- Processes are divided into smaller units called pages.
- Only a subset of pages is loaded into the main memory at any given time.
- Dynamic Page Access:
- Determining in advance which pages a process will require is challenging.
- Page access is dynamic and depends on the execution flow of the process.
- Page Fault:
- If a referenced page is not present in the main memory, it results in a page fault.
- Page fault indicates a miss, and the required page needs to be fetched from secondary memory.
- Page Replacement Algorithm:
- Page replacement algorithms decide which pages to keep in the main memory and which to move to secondary memory.
- These algorithms aim to optimize page usage and minimize page faults.
- High Page Faults Impact:
- If the number of page faults is high, it can significantly impact the effective access time of the system.
- High page faults mean frequent retrieval of pages from slower secondary memory.
What is a Page Fault?
If the referenced page is not in the main memory, it results in a miss, and this concept is referred to as a Page miss or page fault. The CPU must retrieve the missed page from the secondary memory. If the number of page faults is very high, the effective access time of the system will significantly increase.
Conclusion:
In summary, virtual memory allows flexible and efficient use of system resources by managing the presence of process pages in the main memory dynamically. The occurrence of page faults, indicating a miss, triggers the need to fetch pages from secondary memory. Effective page replacement algorithms are crucial for optimizing this process and ensuring smooth system performance.