L-5.19: Virtual Memory | Page fault | Significance of virtual memory | Operating System
Gate Smashers・16 minutes read
Virtual memory allows processes larger than main memory to be executed by dividing processes into pages and utilizing locality of reference to bring related pages into main memory. Page replacement operations like swap-in and swap-out manage pages in main memory, eliminating limitations on process size and number despite main memory constraints.
Insights
- Virtual memory allows processes larger than main memory to run by dividing them into pages and bringing only required pages into main memory, maximizing the number of processes that can be executed despite physical memory limitations.
- The calculation of effective memory access time in virtual memory systems considers the probability of page faults and the time taken for page fault service and main memory access, emphasizing the impact of reducing page faults and increasing page hits on enhancing system performance and avoiding issues like threshing.
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What is virtual memory?
Virtual memory allows processes larger than main memory.
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Summary
00:00
Maximizing Processes with Virtual Memory Technology
- Virtual memory is a concept that allows processes larger than main memory to be executed.
- Main memory size is limited, but virtual memory provides an illusion of executing processes larger than main memory.
- Virtual memory divides processes into pages, bringing only required pages into main memory.
- Locality of reference is utilized to bring related pages into main memory along with the requested page.
- Virtual memory allows parts of multiple processes to be kept in main memory, maximizing the number of processes.
- Page replacement operations like swap-in and swap-out are used to manage pages in main memory.
- Virtual memory eliminates limitations on process size and number, despite main memory constraints.
- Page faults occur when a requested page is absent in main memory, leading to trap generation and control transfer to the operating system.
- Operating system authenticates the user, retrieves the requested page from the hard disk, and places it in an empty slot in main memory.
- Effective memory access time is calculated based on the probability of page faults and the time taken for page fault service and main memory access.
16:59
Optimizing Memory Access in Virtual Systems
- Context switching from user to operating system results in time wastage due to the transfer of control. The operating system searches for data in the slow hard disk, leading to milliseconds wasted in bringing data to the main memory, with page fault service time generally in milliseconds.
- Effective memory access time is calculated as P multiplied by page fault service time plus 1 minus P multiplied by main memory access time. Excessive page faults can lead to threshing, degrading performance, but reducing page faults and increasing page hits can enhance effective memory access time in virtual memory systems.
