Operating Systems, unit: Virtual Memory. Core concepts, terminology, and worked-example cues a college student meets for this unit, building on prior units without repeating them. Front: a term, concept, or short problem cue. Back: the definition, explanation, or answer.
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- What is virtual memory?
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A memory management technique that gives processes the illusion of a large, contiguous address space, backed partly by disk- What is the main benefit of virtual memory?
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Programs can run without being limited by the amount of physical RAM installed- What is demand paging?
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Loading a page into physical memory only when it is actually accessed, not in advance- What is swapping?
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Moving a process's memory between RAM and disk to free up physical memory- What is a swap space (or swap file)?
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A reserved area of disk used to hold pages swapped out of physical memory- What is thrashing?
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A condition where a system spends most of its time swapping pages in and out, with little actual progress- What causes thrashing?
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Too many processes competing for too little physical memory, causing excessive page faults- What is a page replacement algorithm used for?
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Deciding which page to remove from memory when a new page needs to be loaded and memory is full- What is the FIFO page replacement algorithm?
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Replacing the oldest page that was loaded into memory- What is the Least Recently Used (LRU) page replacement algorithm?
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Replacing the page that has not been used for the longest time- What is the Optimal page replacement algorithm?
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Replacing the page that will not be used for the longest time in the future (a theoretical best case)- What is Belady's Anomaly?
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A counterintuitive phenomenon where increasing the number of page frames can increase the number of page faults, seen in FIFO- What is the working set of a process?
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The set of pages a process is actively using during a given time window- What is the effective access time affected by page faults?
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It increases significantly, since disk access is far slower than RAM access- What is copy-on-write, as a memory optimization?
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Sharing memory pages between processes until one attempts to modify it, at which point a private copy is made
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