Virtual Memory
Virtual memory is an operating system technique that gives each process the illusion of a large, contiguous, private address space, while the Kernel transparently maps that virtual address space onto physical RAM (and sometimes disk) behind the scenes.
34 resources across 2 libraries
Glossary Terms(4)
Operating System
An operating system (OS) is the foundational software layer that manages a computer's hardware resources and provides common services to application programs,…
Kernel
The kernel is the core component of an Operating System that has direct control over hardware resources — CPU, memory, and devices — and mediates access to the…
Virtual Memory
Virtual memory is an operating system technique that gives each process the illusion of a large, contiguous, private address space, while the Kernel transparen…
File System
A file system is the method and data structure an Operating System uses to organize, name, store, and retrieve data on persistent storage devices such as hard…
Interview Questions(30)
Difference Between Paging and Segmentation
Paging divides memory into fixed-size blocks called pages (mapped to equal-size frames in physical memory), while segmentation divides memory into variable-siz…
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 Fragmentation?
Fragmentation is the wasted memory that builds up as blocks are allocated and freed over time, leaving usable space scattered in pieces too small or too oddly…
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 is a Translation Lookaside Buffer (TLB)?
A Translation Lookaside Buffer, or TLB, is a small, fast hardware cache inside the CPU that stores recent virtual-to-physical address translations, so the MMU…
What is the Structure of a Page Table?
A page table is a per-process data structure maintained by the operating system that maps virtual page numbers to physical frame numbers, with each entry also…
What is a Multilevel Page Table?
A multilevel page table splits a single flat page table into a hierarchy of smaller tables, where the virtual address is broken into multiple index fields that…
What is an Inverted Page Table?
An inverted page table flips the usual mapping direction by keeping one entry per physical frame instead of one entry per virtual page, storing which process a…
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 Memory Compaction?
Memory compaction is the process of relocating allocated memory blocks so that they sit contiguously, merging the scattered free holes left between them into o…
What is the Memory Hierarchy in a Computer System?
The memory hierarchy is a layered arrangement of storage technologies — registers, cache, main memory, and secondary storage — ordered by decreasing speed and…
What is the Dirty Bit in Paging?
The dirty bit (also called the modified bit) is a single flag in each page table entry that the hardware sets whenever a process writes to that page in memory,…
What is the Reference Bit in Paging?
The reference bit (also called the accessed bit) is a single flag in each page table entry that the hardware sets whenever a page is read or written, giving th…
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