Meta tags:

Headings (most frequently used words):

edit, virtual, memory, navigation, tools, contents, properties, usage, history, paged, segmented, address, space, swapping, see, also, notes, references, further, reading, external, links, menu, page, tables, paging, supervisor, pinned, pages, thrashing, personal, namespaces, views, search, contribute, print, export, in, other, projects, languages, real, operation,

Text of the page (most frequently used words):
the (244), #memory (149), and (90), virtual (85), page (69), for (62), systems (48), that (41), system (38), #address (38), paging (35), operating (25), this (24), real (23), ibm (23), with (22), from (22), management (22), space (22), pages (21), are (21), may (20), not (20), addresses (20), edit (19), computer (19), into (19), used (18), storage (18), time (17), segment (17), was (16), segmentation (16), hardware (15), can (15), such (15), use (13), pdf (13), retrieved (13), supervisor (13), which (13), there (13), tables (12), some (12), one (11), fault (11), file (10), all (10), translation (10), program (10), term (10), pinned (10), using (9), reference (9), mode (9), table (9), multics (9), swapping (9), only (9), when (9), application (9), than (9), wikipedia (8), main (8), articles (8), 360 (8), spaces (8), but (8), multiple (8), data (8), fixed (8), free (8), more (7), different (7), first (7), unit (7), isbn (7), doi (7), part (7), burroughs (7), 370 (7), atlas (7), model (7), had (7), out (7), code (7), have (7), segments (7), large (7), frame (7), will (7), available (6), additional (6), 2022 (6), other (6), read (6), short (6), software (6), pointer (6), programs (6), has (6), architecture (6), 2017 (6), support (6), early (6), also (6), same (6), swap (6), operation (6), trap (6), need (6), their (6), single (6), process (6), each (6), physical (6), secondary (6), technique (6), about (5), september (5), links (5), information (5), article (5), history (5), 2010 (5), automatic (5), garbage (5), algorithm (5), allocation (5), x86 (5), sharing (5), october (5), 978 (5), design (5), implementations (5), applications (5), virtualization (5), cache (5), see (5), example (5), instruction (5), those (5), files (5), provided (5), because (5), mapped (5), processes (5), usually (5), store (5), buffers (5), were (5), exception (5), primary (5), version (4), changes (4), contents (4), unsourced (4), statements (4), references (4), december (4), november (4), list (4), university (4), org (4), control (4), algorithms (4), variable (4), buffer (4), manual (4), protected (4), archived (4), machine (4), 1971 (4), programming (4), mechanisms (4), introduction (4), original (4), set (4), its (4), performance (4), release (4), dos (4), level (4), concept (4), computing (4), embedded (4), usage (4), drums (4), does (4), require (4), properties (4), make (4), then (4), back (4), they (4), been (4), paged (4), pointers (4), contain (4), between (4), instead (4), intel (4), thrashing (4), working (4), older (4), pageable (4), measured (4), rather (4), these (4), without (4), devices (4), access (4), even (4), registers (4), frames (4), contiguous (4), introduced (4), computers (4), words (4), güntsch (4), form (4), very (4), run (4), terms (3), non (3), special (3), help (3), navigation (3), wayback (3), april (3), cs1 (3), german (3), manchester (3), based (3), over (3), collection (3), collector (3), new (3), dynamic (3), mmu (3), windows (3), tss (3), arpaci (3), dusseau (3), 2014 (3), game (3), most (3), 1972 (3), s2cid (3), 1145 (3), acm (3), corporation (3), built (3), 1962 (3), jessen (3), 2004 (3), before (3), 2015 (3), vs1 (3), through (3), cpu (3), unswappable (3), provide (3), occurs (3), currently (3), automatically (3), work (3), causes (3), within (3), number (3), reside (3), providing (3), hence (3), called (3), active (3), response (3), another (3), parts (3), interrupt (3), locked (3), never (3), many (3), long (3), often (3), less (3), must (3), assigned (3), due (3), typically (3), however (3), managing (3), sizes (3), combination (3), running (3), entry (3), larger (3), expensive (3), implemented (3), commercial (3), mainframes (3), developed (3), exactly (3), include (3), modern (3), thus (3), 1960s (3), view (2), contact (2), privacy (2), policy (2), text (2), under (2), wikimedia (2), foundation (2), commons (2), simple (2), english (2), bahasa (2), wikidata (2), cite (2), link (2), upload (2), related (2), what (2), here (2), tools (2), learn (2), current (2), search (2), talk (2), create (2), personal (2), categories (2), template (2), needing (2), february (2), 2021 (2), description (2), maint (2), numeric (2), names (2), authors (2), sources (2), https (2), virtual_memory (2), libraries (2), fragmentation (2), stack (2), overflow (2), strong (2), counting (2), mark (2), concurrent (2), demand (2), input (2), tlb (2), lookaside (2), june (2), microsoft (2), technology (2), linux (2), kernel (2), conference (2), scheduling (2), mainframe (2), mts (2), advanced (2), books (2), three (2), easy (2), external (2), john (2), david (2), further (2), reading (2), mvs (2), authorized (2), 1990 (2), 2016 (2), transwap (2), important (2), press (2), structure (2), execution (2), communications (2), machines (2), january (2), 1968 (2), 645 (2), 2013 (2), b5500 (2), 2009 (2), india (2), july (2), guide (2), sayre (2), 1969 (2), efficient (2), enough (2), 2002 (2), vol (2), afips (2), 1109 (2), 1996 (2), publishers (2), processors (2), journal (2), research (2), origin (2), issn (2), peter (2), amd (2), direct (2), components (2), previously (2), did (2), uses (2), contemporary (2), notes (2), series (2), intended (2), ram (2), swapped (2), area (2), provides (2), any (2), name (2), flag (2), addition (2), temporarily (2), sysevent (2), call (2), vs2 (2), entire (2), mapping (2), places (2), multi (2), section (2), attempt (2), indirect (2), offset (2), maps (2), executing (2), map (2), difference (2), length (2), consists (2), two (2), protection (2), whereas (2), guest (2), needs (2), user (2), like (2), 80386 (2), dividing (2), similar (2), 80286 (2), segmented (2), down (2), useful (2), task (2), order (2), progress (2), adding (2), stealing (2), citation (2), needed (2), wired (2), made (2), nonpageable (2), specification (2), unix (2), mlock (2), structures (2), wall (2), clock (2), possibly (2), indeed (2), facility (2), fast (2), fixing (2), consuming (2), while (2), whether (2), cannot (2), could (2), lost (2), delays (2), permanently (2), otherwise (2), wouldn (2), necessary (2), periods (2), others (2), rely (2), handlers (2), containing (2), would (2), queue (2), replacement (2), valid (2), write (2), copy (2), error (2), stolen (2), loaded (2), stored (2), allow (2), handle (2), creates (2), manages (2), added (2), least (2), separate (2), range (2), translate (2), seen (2), specific (2), blocks (2), generally (2), citations (2), improve (2), exceptions (2), problems (2), utilizing (2), 1970s (2), means (2), users (2), during (2), models (2), true (2), programmer (2), b5000 (2), core (2), feature (2), his (2), high (2), speed (2), extend (2), multiprogramming (2), unpredictable (2), requires (2), own (2), dedicated (2), appears (2), ability (2), security (2), physically (2), show (2), jump (2), web (2), sep (2), cookie, statement, statistics, developers, mobile, disclaimers, apply, site, you, agree, registered, trademark, profit, organization, inc, creative, attribution, sharealike, license, last, edited, utc, tiếng, việt, українська, türkçe, svenska, suomi, српски, srpski, slovenščina, slovenčina, සිංහල, shqip, русский, português, polski, norsk, bokmål, 日本語, nederlands, melayu, magyar, lietuvių, кыргызча, қазақша, עברית, italiano, indonesia, हिन्दी, հայերեն, 한국어, galego, français, فارسی, euskara, esperanto, español, ελληνικά, eesti, deutsch, dansk, čeština, català, беларуская, тарашкевіца, العربية, languages, projects, printable, download, print, export, item, permanent, recent, community, portal, contribute, donate, random, events, views, namespaces, log, account, contributions, logged, menu, hidden, gnd, identifiers, webarchive, disputed, accuracy, disputes, dmy, dates, language, department, science, index, php, title, oldid, 1111399572, germany, authority, national, region, international, symposium, unreachable, leak, issues, dangling, safety, weak, tracing, compact, finalizer, sweep, cheney, boehm, delete, static, ptmalloc, mimalloc, jemalloc, hoard, malloc, dlmalloc, 8086, compression, iommu, output, function, manager, randy, kath, developer, network, group, 1992, mailing, discussion, birth, linuxmm, michael, alexander, michigan, engineering, summer, 1970, revised, compares, resource, approaches, including, four, topics, remzi, andrea, relevant, chapters, policies, tlbs, pieces, wikisource, hennessy, patterson, 55860, 724, quantitative, approach, assembler, services, wto, sa23, 1375, knowledge, center, dontswap, okswap, requesting, preferred, requirement, apf, organick, elliott, mit, 262, 15012, examination, multicians, environment, bensoussan, andré, clingen, charlest, daley, robert, 308, 318, 6434322, 355602, 361306, 6731, citeseerx, concepts, smith, uhlig, august, 2005, hotchips, tutorial, architectures, glaser, edward, couleur, oliver, 2007, overview, vyssotsky, corbató, 1964, 1021326, processing, sharma, excel, 7446, 626, quintero, dino, 138, 0738437668, power, implementing, optimizing, folding, displace, 656, 660, 15655353, 363626, 363629, book, copyright, corp, gc24, 5991, general, gary, allred, 164, spring, joint, integrated, emulation, cragon, harvey, jones, bartlett, 113, 86720, 474, pipelined, joyner, ian, creasy, 1981, 486, development, ferranti, kilburn, edwards, lanigan, sumner, 223, 235, tec, 5219356, ire, trans, liptay, structural, aspects, 1147, 0015, die, entwicklung, des, virtuellen, speichers, 216, 219, 11514875, 0170, 6012, 1007, s002870050034, informatik, spektrum, elke, ieee, annals, 1997, beginning, recollections, pioneers, denning, 2011, march, nested, zhou, xiangrong, petrov, 2008, 1539, 9087, 1457246, 1457251, transactions, energy, haldar, sibsankar, aravind, alex, alagarsamy, pearson, education, 269, 8131730225, bhattacharjee, abhishek, lustig, daniel, morgan, claypool, 9781627056021, architectural, 2020, ga32, 0887, bcp, base, 1966, c20, 1647, preliminary, technical, summary, relocation, supported, hypervisor, involve, runs, solid, state, disks, specifications, unify, graphic, card, heterogeneous, cuda, allows, necessarily, jobs, marking, doing, pin, done, duration, job, entering, eligible, privileged, svc, certain, whatever, facilities, writes, reads, calls, mapviewoffile, inter, semi, arbitrary, always, boundary, linkage, load, register, unresolved, contains, indication, refers, handler, puts, tag, field, longer, returns, where, occurred, caused, eliminates, completely, works, private, linker, win32, mmap, consequences, way, lengthen, differentiation, potential, later, linear, moved, levels, few, assisted, solutions, combined, offers, domains, vmm, division, visible, semantics, looks, structured, bit, supports, scheme, option, rarely, together, predominant, problem, occur, spends, unsuitably, amount, transferring, backing, slowing, minimum, should, insufficient, sets, simplest, improving, solution, reduce, tasks, reduces, oses, managed, every, corresponds, standard, modes, refer, simply, man, openvms, successor, unfixed, seconds, fractions, second, significantly, tens, milliseconds, performed, resorting, accessed, directly, peripheral, attached, expect, find, located, regardless, bus, transfers, stopped, restarted, processed, come, measurement, sensor, got, recovered, buses, channels, timing, dependent, avoid, drivers, still, areas, array, completion, invoke, handling, become, far, complex, particularly, case, interruptions, empty, cases, update, followed, purging, restarts, old, copied, treated, desired, reused, uninitialized, cleared, invalid, treats, resolved, results, abnormal, termination, errors, several, ways, depending, details, lists, ensure, quickly, resolve, faults, periodically, steal, allocated, lru, modified, written, auxiliary, responsible, nor, recently, earlier, smaller, sds, 940, whole, tree, redirect, instructions, handles, known, holds, indicating, corresponding, indicates, raises, invoking, component, nearly, divide, size, ranges, amounts, kilobytes, how, remove, message, please, material, challenged, removed, reliable, verification, processor, scaled, poorly, underneath, existing, layer, enabling, chain, loading, descriptors, causing, designers, strictly, double, mainstream, addressed, required, difficult, build, specialized, initial, slowed, slightly, worries, wide, effective, debate, team, led, showed, overlay, consistently, worked, better, best, manually, controlled, throughout, business, migrate, fewer, powerful, improved, price, introduce, norwegian, minicomputers, notably, vms, vax, nord, minicomputer, start, interpretive, 3081, versions, exploit, sie, hypervisors, mechanism, consisted, 384, 304, commissioned, prototypes, 1959, 1961, independently, released, drum, claim, 1956, doctoral, thesis, stand, careful, scrutiny, proposed, key, invent, since, taken, wrote, quoted, respect, existence, know, exists, sort, situation, earliest, examples, referring, semiconductor, invisible, held, analogous, designed, solve, involved, sic, logical, digital, asynchronous, rotating, technische, universität, berlin, fritz, rudolf, physicist, 1950s, logic, therefore, extension, possible, programmers, divided, via, pdp, multitasking, overlaying, purpose, consistent, times, opt, decreased, trigger, produce, unwanted, especially, significant, chip, implement, chips, reason, don, traps, determinism, sole, ones, composed, virtualized, svs, 70s, demands, savings, incentive, switch, capability, reliability, making, attractive, marketplace, rca, spectra, cms, mcp, electrologica, integral, employ, increase, mid, 1980s, functionality, though, notable, discuss, dubious, emulators, considered, generalization, makes, easier, hiding, delegating, burden, eliminating, explicitly, obviating, relative, addressing, relocate, overlays, hierarchy, benefits, freeing, having, manage, shared, share, increased, isolation, being, able, conceptually, might, assignment, referred, translates, capabilities, exceed, capacity, present, disk, idealized, abstraction, resources, actually, given, illusion, combines, inactive, dasd, pooling, tbn, encyclopedia, http, archive, 20221016123727, wiki, timestamps, capture, fail, success, 2023, nov, oct, feb, 2026, 310, captures,

Text of the page (random words):
e invisible to the user held the contents of parts of the main store in use by the currently executing program this is exactly analogous to güntsch s system designed as a means to improve performance rather than to solve the problems involved in multi programming the university of manchester atlas computer was the first computer to feature true virtual memory the first true virtual memory system was that implemented at the university of manchester to create a one level storage system 13 as part of the atlas computer it used a paging mechanism to map the virtual addresses available to the programmer on to the real memory that consisted of 16 384 words of primary core memory with an additional 98 304 words of secondary drum memory 14 the first atlas was commissioned in 1962 but working prototypes of paging had been developed by 1959 8 2 15 16 in 1961 the burroughs corporation independently released the first commercial computer with virtual memory the b5000 with segmentation rather than paging 17 18 ibm developed c the concept of hypervisors in their cp 40 and cp 67 and in 1972 provided it for the s 370 as virtual machine facility 370 20 ibm introduced the start interpretive execution sie instruction as part of 370 xa on the 3081 and vm xa versions of vm to exploit it before virtual memory could be implemented in mainstream operating systems many problems had to be addressed dynamic address translation required expensive and difficult to build specialized hardware initial implementations slowed down access to memory slightly 8 there were worries that new system wide algorithms utilizing secondary storage would be less effective than previously used application specific algorithms by 1969 the debate over virtual memory for commercial computers was over 8 an ibm research team led by david sayre showed that their virtual memory overlay system consistently worked better than the best manually controlled systems 21 throughout the 1970s the ibm 370 series running their virtual storage based operating systems provided a means for business users to migrate multiple older systems into fewer more powerful mainframes that had improved price performance the first minicomputer to introduce virtual memory was the norwegian nord 1 during the 1970s other minicomputers implemented virtual memory notably vax models running vms virtual memory was introduced to the x86 architecture with the protected mode of the intel 80286 processor but its segment swapping technique scaled poorly to larger segment sizes the intel 80386 introduced paging support underneath the existing segmentation layer enabling the page fault exception to chain with other exceptions without double fault however loading segment descriptors was an expensive operation causing operating system designers to rely strictly on paging rather than a combination of paging and segmentation citation needed paged virtual memory edit see also memory paging this section needs additional citations for verification please help improve this article by adding citations to reliable sources unsourced material may be challenged and removed december 2010 learn how and when to remove this template message nearly all current implementations of virtual memory divide a virtual address space into pages blocks of contiguous virtual memory addresses pages on contemporary d systems are usually at least 4 kilobytes in size systems with large virtual address ranges or amounts of real memory generally use larger page sizes 22 page tables edit page tables are used to translate the virtual addresses seen by the application into physical addresses used by the hardware to process instructions 23 such hardware that handles this specific translation is often known as the memory management unit each entry in the page table holds a flag indicating whether the corresponding page is in real memory or not if it is in real memory the page table entry will contain the real memory address at which the page is stored when a reference is made to a page by the hardware if the page table entry for the page indicates that it is not currently in real memory the hardware raises a page fault exception invoking the paging supervisor component of the operating system systems can have one page table for the whole system separate page tables for each application and segment a tree of page tables for large segments or some combination of these if there is only one page table different applications running at the same time use different parts of a single range of virtual addresses if there are multiple page or segment tables there are multiple virtual address spaces and concurrent applications with separate page tables redirect to different real addresses some earlier systems with smaller real memory sizes such as the sds 940 used page registers instead of page tables in memory for address translation paging supervisor edit this part of the operating system creates and manages page tables and lists of free page frames in order to ensure that there will be enough free page frames to quickly resolve page faults the system may periodically steal allocated page frames using a page replacement algorithm e g a least recently used lru algorithm stolen page frames that have been modified are written back to auxiliary storage before they are added to the free queue on some systems the paging supervisor is also responsible for managing translation registers that are nor automatically loaded from page tables typically a page fault that cannot be resolved results in an abnormal termination of the application however some systems allow the application to have exception handlers for such errors the paging supervisor may handle a page fault exception in several different ways depending on the details if the virtual address is invalid the paging supervisor treats it as an error if the page is valid and the page information is not loaded into the mmu the page information will be stored into one of the page registers if the page is uninitialized a new page frame may be assigned and cleared if there is a stolen page frame containing the desired page that page frame will be reused for a fault due to a write attempt into a read protected page if it is a copy on write page then a free page frame will be assigned and the contents of the old page copied otherwise it is treated as an error if the virtual address is a valid page in a memory mapped file or a paging file a free page frame will be assigned and the page read in in most cases there will be an update to the page table possibly followed by purging the translation lookaside buffer tlb and the system restarts the instruction that causes the exception if the free page frame queue is empty then the paging supervisor must free a page frame using the same page replacement algorithm for page stealing pinned pages edit operating systems have memory areas that are pinned never swapped to secondary storage other terms used are locked fixed or wired pages for example interrupt mechanisms rely on an array of pointers to their handlers such as i o completion and page fault if the pages containing these pointers or the code that they invoke were pageable interrupt handling would become far more complex and time consuming particularly in the case of page fault interruptions hence some part of the page table structures is not pageable some pages may be pinned for short periods of time others may be pinned for long periods of time and still others may need to be permanently pinned for example the paging supervisor code and drivers for secondary storage devices on which pages reside must be permanently pinned as otherwise paging wouldn t even work because the necessary code wouldn t be available timing dependent components may be pinned to avoid variable paging delays data buffers that are accessed directly by peripheral devices that use direct memory access or i o channels must reside in pinned pages while the i o operation is in progress because such devices and the buses to which they are attached expect to find data buffers located at physical memory addresses regardless of whether the bus has a memory management unit for i o transfers cannot be stopped if a page fault occurs and then restarted when the page fault has been processed for example the data could come from a measurement sensor unit and lost real time data that got lost because of a page fault can t be recovered in ibm s operating systems for system 370 and successor systems the term is fixed and such pages may be long term fixed or may be short term fixed or may be unfixed i e pageable system control structures are often long term fixed measured in wall clock time i e time measured in seconds rather than time measured in fractions of one second whereas i o buffers are usually short term fixed usually measured in significantly less than wall clock time possibly for tens of milliseconds indeed the os has a special facility for fast fixing these short term fixed data buffers fixing which is performed without resorting to a time consuming supervisor call instruction multics used the term wired openvms and windows refer to pages temporarily made nonpageable as for i o buffers as locked and simply nonpageable for those that are never pageable the single unix specification also uses the term locked in the specification for mlock as do the mlock man pages on many unix like systems virtual real operation edit in os vs1 and similar oses some parts of systems memory are managed in virtual real mode called v r in this mode every virtual address corresponds to the same real address this mode is used for interrupt mechanisms for the paging supervisor and page tables in older systems and for application programs using non standard i o management for example ibm s z os has 3 modes virtual virtual virtual real and virtual fixed citation needed thrashing edit when paging and page stealing are used a problem called thrashing can occur in which the computer spends an unsuitably large amount of time transferring pages to and from a backing store hence slowing down useful work a task s working set is the minimum set of pages that should be in memory in order for it to make useful progress thrashing occurs when there is insufficient memory available to store the working sets of all active programs adding real memory is the simplest response but improving application design scheduling and memory usage can help another solution is to reduce the number of active tasks on the system this reduces demand on real memory by swapping out the entire working set of one or more processes segmented virtual memory edit some systems such as the burroughs b5500 24 use segmentation instead of paging dividing virtual address spaces into variable length segments a virtual address here consists of a segment number and an offset within the segment the intel 80286 supports a similar segmentation scheme as an option but it is rarely used segmentation and paging can be used together by dividing each segment into pages systems with this memory structure such as multics and ibm system 38 are usually paging predominant segmentation providing memory protection 25 26 27 in the intel 80386 and later ia 32 processors the segments reside in a 32 bit linear paged address space segments can be moved in and out of that space pages there can page in and out of main memory providing two levels of virtual memory few if any operating systems do so instead using only paging early non hardware assisted x86 virtualization solutions combined paging and segmentation because x86 paging offers only two protection domains whereas a vmm guest os or guest application stack needs three 28 22 the difference between paging and segmentation systems is not only about memory division segmentation is visible to user processes as part of memory model semantics hence instead of memory that looks like a single large space it is structured into multiple spaces this difference has important consequences a segment is not a page with variable length or a simple way to lengthen the address space segmentation that can provide a single level memory model in which there is no differentiation between process memory and file system consists of only a list of segments files mapped into the process s potential address space 29 this is not the same as the mechanisms provided by calls such as mmap and win32 s mapviewoffile because inter file pointers do not work when mapping files into semi arbitrary places in multics a file or a segment from a multi segment file is mapped into a segment in the address space so files are always mapped at a segment boundary a file s linkage section can contain pointers for which an attempt to load the pointer into a register or make an indirect reference through it causes a trap the unresolved pointer contains an indication of the name of the segment to which the pointer refers and an offset within the segment the handler for the trap maps the segment into the address space puts the segment number into the pointer changes the tag field in the pointer so that it no longer causes a trap and returns to the code where the trap occurred re executing the instruction that caused the trap 30 this eliminates the need for a linker completely 8 and works when different processes map the same file into different places in their private address spaces 31 address space swapping edit some operating systems provide for swapping entire address spaces in addition to whatever facilities they have for paging and segmentation when this occurs the os writes those pages and segments currently in real memory to swap files in a swap in the os reads back the data from the swap files but does not automatically read back pages that had been paged out at the time of the swap out operation ibm s mvs from os vs2 release 2 through z os provides for marking an address space as unswappable doing so does not pin any pages in the address space this can be done for the duration of a job by entering the name of an eligible 32 main program in the program properties table with an unswappable flag in addition privileged code can temporarily make an address space unswappable using a sysevent supervisor call instruction svc certain changes 33 in the address space properties require that the os swap it out and then swap it back in using sysevent transwap 34 swapping does not necessarily require memory management hardware if for example multiple jobs are swapped in and out of the same area of storage see also edit cpu design page computing cache algorithms memory allocation memory management operating systems protected mode an x86 mode that allows for virtual memory cuda pinned memory heterogeneous system architecture a series of specifications intended to unify ram and graphic s card memory storage virtualization notes edit early systems used drums contemporary systems use disks or solid state memory ibm uses the term virtual storage on mainframe...