Page Fault

What is Virtual Memory?

Virtual memory is a technique that gives each process the illusion of a large, private, contiguous address space by mapping virtual addresses to physical RAM (…

What is Thrashing in Operating Systems?

Thrashing is a state where a system spends most of its time swapping pages between RAM and disk rather than executing actual instructions, causing CPU utilizat…

What is a Page Fault?

A page fault is a hardware trap raised by the MMU when a running program accesses a virtual memory page that is not currently mapped to a physical frame, forci…

What is Demand Paging?

Demand paging is a virtual memory technique where a page is loaded into physical memory only when a process actually references it, rather than loading the who…

What is the LRU Page Replacement Algorithm?

Least Recently Used (LRU) page replacement evicts the page that has gone the longest without being referenced, on the assumption that pages accessed far in the…

What is the FIFO Page Replacement Algorithm?

First-In-First-Out (FIFO) page replacement evicts the page that has been resident in memory the longest, regardless of how recently or frequently it has actual…

What is the Optimal (OPT/Belady’s) Page Replacement Algorithm?

The Optimal page replacement algorithm — also called OPT or Belady’s algorithm — evicts the page that will not be used for the longest time in the future, whic…

What is the Clock (Second-Chance) Page Replacement Algorithm?

The Clock algorithm, also called second-chance, approximates LRU cheaply by arranging resident pages in a circular list with a single reference bit each, sweep…

What is the LFU Page Replacement Algorithm?

Least Frequently Used (LFU) page replacement evicts the page with the smallest access count, on the assumption that pages referenced rarely overall are less va…

What is Belady’s Anomaly?

Belady’s Anomaly is the counter-intuitive situation where increasing the number of page frames available to a process actually increases the number of page fau…

What are Memory-Mapped Files?

A memory-mapped file is a file whose contents are mapped directly into a process’s virtual address space via the page cache, so the program reads and writes th…

What is Copy-on-Write (COW)?

Copy-on-write is an optimization where two entities share the same underlying physical memory pages read-only until one of them attempts to modify the data, at…

What is Swapping in Operating Systems?

Swapping is the OS technique of moving an entire process or individual memory pages out of physical RAM to a reserved area of disk (the swap space) to free up…

What is the Working Set Model?

The working set model defines a process's working set as the set of pages it has referenced within a recent time window (delta), and the OS uses this to decide…

What is Pure Demand Paging?

Pure demand paging is a memory management policy where absolutely no page of a process is loaded into RAM until the process actually references it, so every pr…

What is Prepaging?

Prepaging is a memory management optimization where the OS loads a batch of pages it predicts a process will need into RAM before they are actually referenced,…

What Does the mmap() System Call Do?

mmap() maps a file (or anonymous memory) directly into a process’s virtual address space, so the program can read and write the file’s contents using ordinary…