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Encyclopedia > Paging

In computer operating systems that have their main memory divided into pages, paging (sometimes called swapping) is a transfer of pages between main memory and an auxiliary store, such as hard disk drive.[1] Paging is an important part of virtual memory implementation in most contemporary general-purpose operating systems, allowing them to easily use disk storage for data that does not fit into physical RAM. Paging is usually implemented as a task built into the kernel of the operating system. For terminal pagers, see more (Unix) or less (Unix). ... Radio Paging is still in use today (2006) by organisations who need to send urgent information to people quickly and cheaply. ... Bank switching (also known as paging, but only loosely related to the ordinary meaning of paging in computing) was a technique common in 8-bit microcomputer systems, to increase the amount of addressable RAM and ROM without extending the address bus. ... This article is about the machine. ... An operating system (OS) is a software that manages computer resources and provides programmers with an interface used to access those resources. ... Primary storage is a category of computer storage, often called main memory. ... In a context of computer virtual memory, a page, memory page, or virtual page is a fixed-length block of main memory, that is contiguous in both physical memory addressing and virtual memory addressing. ... A hard disk drive (HDD), commonly referred to as a hard drive, hard disk or fixed disk drive,[1] is a non-volatile storage device which stores digitally encoded data on rapidly rotating platters with magnetic surfaces. ... This article is about the computer term. ... A task is an execution path through address space. In other words, a set of program instructions that is loaded in memory. ... A kernel connects the application software to the hardware of a computer. ...

Contents

Overview

The main functions of paging are performed when a program tries to access pages that do not currently reside in RAM. This situation is known as a page fault. The Operating System must then take control and handle the page fault, in a manner invisible to the program. Therefore, the operating system must: Look up RAM, Ram, ram in Wiktionary, the free dictionary. ... In computer storage technology, a page is a fixed length block of memory that is used as a unit of transfer between physical memory and external storage like a disk, and a page fault is an interrupt (or exception) to the software raised by the hardware, when a program accesses...

  1. Determine the location of the data in auxiliary storage.
  2. Obtain an empty page frame in RAM to use as a container for the data.
  3. Load the requested data into the available page frame.
  4. Return control to the program, transparently retrying the instruction that caused page fault.

The need to reference memory at a particular address arises from two main sources: In computer science, an instruction typically refers to a single operation of a processor within a computer architecture. ...

  • Processor trying to load and execute a program's instructions itself.
  • Data being accessed by a program's instruction.

In step 2, when a page has to be loaded and all existing pages in RAM are currently in use, one of the existing pages must be swapped with the requested new page. The paging system must determine the page to swap by choosing one that is least likely to be needed within a short time. There are various page replacement algorithms that try to answer such issue. CPU redirects here. ... Look up RAM, Ram, ram in Wiktionary, the free dictionary. ... It has been suggested that this article or section be merged into cache algorithms. ...


Most operating systems use the least recently used (LRU) page replacement algorithm. The theory behind LRU is that the least recently used page is the most likely one not to be needed shortly; when a new page is needed, the least recently used page is discarded. This algorithm is most often correct but not always: e.g. a sequential process moves forward through memory and never again accesses the most recently used page. Cache algorithms are optimizing instructions â€“ algorithms â€“ that a computer program can follow to manage a cache of information stored on the computer. ...


If a page chosen to be swapped has been modified since loading (if page is dirty), it has to be written to auxiliary storage, otherwise it is simply discarded.


In addition to swapping in pages because they are necessary, in reaction to a page fault, there are several strategies for guessing what pages might be needed, and speculatively pre-loading them.


Demand paging

Main article: Demand paging

Demand paging refuses to guess. With demand paging, no pages are brought into RAM until necessary. In particular, with demand paging, a program usually begins execution with none of its pages pre-loaded in RAM. Pages are copied from the executable file into RAM the first time the executing code references them, usually in response to a page fault. During a particular run of a program, pages of the executable file that implement functionality not used on that particular run are never loaded. In computer operating systems, demand paging is an application of virtual memory. ... In computer storage technology, a page is a fixed length block of memory that is used as a unit of transfer between physical memory and external storage like a disk, and a page fault is an interrupt (or exception) to the software raised by the hardware, when a program accesses...


Loader paging

Loader paging[original research?] guesses that the entire program will be used. Many operating systems (including those with a relocating loader) load every page of a program into RAM before beginning to execute the program. In computing, a loader is a program that performs the functions of a linker program and then immediately schedules the resulting executable program for action (in the form of a memory image), without necessarily saving the program as an executable file. ...


Anticipatory paging

Technique that preloads a process's nonresident pages that are likely to be referenced in the near future. Such strategies attempt to reduce the number of page faults a process experiences


Swap prefetch

A few operating systems use anticipatory paging, also called swap prefetch. These operating systems periodically attempt to guess which pages will soon be needed, and start loading them into RAM. There are various heuristics in use, such as "if a program references one virtual address which causes a page fault, perhaps the next few pages' worth of virtual address space will soon be used" and "if one big program just finished execution, leaving lots of free RAM, perhaps the user will return to using some of the programs that were recently paged out".


Precleaning

Unix operating systems periodically use sync to pre-clean all dirty pages. This makes starting a large new program run much faster, because it can be loaded into page frames that held clean pages that were dropped, rather than being loaded into page frames that were dirty and needed to be written back to disk before they were dropped. sync is a standard system call in the Unix operating system, which commits to disk all data in the kernel filesystem buffers, i. ...


Thrashing

Most programs reach a steady state in their demand for memory locality both in terms of instructions fetched and data being accessed. This steady state is usually much less than the total memory required by the program. This steady state is sometimes referred to as the working set: the set of memory pages that are most frequently accessed. In computer science, thrash is the poor performance of a virtual memory (or paging) system, when the same pages are being loaded repeatedly due to a lack of main memory. ... It has been suggested that this article or section be merged with Memory locality. ... Working set is the set of physical memory pages currently dedicated to a specific process. ...


Virtual memory systems work most efficiently when the ratio of the working set to the total number of pages that can be stored in RAM is low enough to minimize the number of page faults. A program that works with huge data structures will sometimes require a working set that is too large to be efficiently managed by the page system resulting in constant page faults that drastically slow down the system. This condition is referred to as thrashing: pages are swapped out and then accessed causing frequent faults. In computer science, thrash is the poor performance of a virtual memory (or paging) system, when the same pages are being loaded repeatedly due to a lack of main memory. ...


An interesting characteristic of thrashing is that as the working set grows, there is very little increase in the number of faults until the critical point (when faults go up dramatically and majority of system's processing power is spent on handling them).


An extreme example of this sort of situation occurred on the IBM System/360 Model 67 and IBM System/370 series mainframe computers, in which a particular instruction could consist of an execute instruction, which crosses a page boundary, that the instruction points to a move instruction, that itself also crosses a page boundary, targeting a move of data from a source that crosses a page boundary, to a target of data that also crosses a page boundary. The total amount of pages thus being used by this particular instruction is eight, and all eight pages must be present in memory at the same time. If the operating system will allocate less than eight pages of actual memory in this example, when it attempts to swap out some part of the instruction or data to bring in the remainder, the instruction will again page fault, and it will thrash on every attempt to restart the failing instruction. The IBM System/370 (often: S/370) was a model range of IBM mainframes announced on June 30, 1970 as the successors to the System/360 family. ...


To decrease excessive paging, and thus possibly resolve thrashing problem, a user can do any of the following:

  • Increase the amount of RAM in the computer (generally the best long-term solution).
  • Decrease the number of programs being concurrently run on the computer.

The term thrashing is also used in contexts other than virtual memory systems, for example to describe cache issues in computing or silly window syndrome in networking. For other uses, see cache (disambiguation). ... Categories: Possible copyright violations ...


Terminology differences - paging versus swapping

Historically, paging sometimes also referred simply to memory allocation scheme using fixed-length pages as opposed to variable-length segments, and without implicit suggestion that virtual memory technique is employed at all or that those pages are transferred to disk.[2] [3] Such usage is rare today. It has been suggested that this article or section be merged with Dynamic memory allocation. ... Segmentation is one of the most common ways to achieve memory protection; another common one is paging. ...


Some modern systems use the term swapping along with paging. Historically, swapping referred to moving from/to secondary storage a whole program at a time, in a scheme known as roll-in/roll-out. [4] [5] In 1960s, after the concept of virtual memory was introduced—in two variants, either using segments or pages—and swapping was applied to moving, respectively, either segments or pages, between disk and memory. Today with the virtual memory mostly based on pages, not segments, swapping became a fairly close synonym of paging, although with one difference. The 1960s decade refers to the years from the beginning of 1960 to the end of 1969. ...


In many popular systems, there is a concept known as page cache, of using the same single mechanism for both virtual memory and disk caching. A page may be then transferred to or from any ordinary disk file, not necessarily a dedicated space. In some of such systems, notably Unix-like including Linux, swapping only refers to virtual memory scope and paging to both. Page in is transferring a page from the disk to RAM. Page out is transferring a page from RAM to the disk. But swap in and out only refer to transferring pages between RAM and dedicated swap space or swap file, and not any other place on disk. In computing, page cache, sometimes ambiguously called disk cache, is a transparent cache of disk-backed pages kept in primary storage (RAM) for quicker access. ... For other uses, see cache (disambiguation). ... Diagram of the relationships between several Unix-like systems A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. ... This article is about operating systems that use the Linux kernel. ...


On the other hand, Microsoft systems from Windows NT line very rarely use the term swapping to differentiate from general paging, and call the dedicated secondary store just a page file. Microsoft Corporation, (NASDAQ: MSFT, HKSE: 4338) is a multinational computer technology corporation with global annual revenue of US$44. ... Windows NT (New Technology) is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. ...


Paging in Windows 3.0 line

Virtual memory has been a feature of Microsoft Windows since Windows 3.0 in 1990. Microsoft introduced virtual memory in response to the failures of Windows 1.0 and Windows 2.0, attempting to slash resource requirements for the operating system. Windows redirects here. ... Windows 3. ... Windows 1. ... Windows 2. ...


Confusion abounds about Microsoft's decision to refer to the swap file as "virtual memory". Novices unfamiliar with the concept accept this definition without question, and speak of adjusting Windows' virtual memory size. In fact every process has a fixed, unchangeable virtual memory size, usually 2 GiB. The user has only an option to change disk capacity dedicated to paging. The term gib may refer to: a castrated male cat or ferret an abbreviation for gibibyte (GiB) or gibibit (Gib) an abbreviation for Gibraltar an abbreviation for Gib Board, itself an abbreviation of Gibraltar Board, all Winston Wallboards[1] tradenames for drywall (plasterboard). ...


Windows 3.x creates a hidden file named 386SPART.PAR or WIN386.SWP for use as a swap file. It is generally found in the root directory, but it may appear elsewhere (typically in the WINDOWS directory). Its size depends on how much swap space the system has (a setting selected by the user under Control Panel → Enhanced under "Virtual Memory".) If the user moves or deletes this file, a blue screen will appear the next time Windows is started, with the error message "The permanent swap file is corrupt". The user will be prompted to choose whether or not to delete the file (whether or not it exists). There are very few or no other articles that link to this one. ... In computer file systems, the root directory is the first or top-most directory in a hierarchy. ... Control Panel is part of the Windows graphical user interface (GUI) menu accessible from the Start Menu which allows users to view and manipulate basic system settings and controls, such as adding hardware, adding/removing software, controlling user accounts, changing accessibility options etc. ... A blue screen of death as seen in Windows XP and Vista. ... This page is a candidate for speedy deletion. ...


Windows 95 uses a similar file, and the settings for it are located under Control Panel → System → Performance tab → Virtual Memory. Windows automatically sets the size of the page file to start at 1.5× the size of physical memory, and expand up to 3× physical memory if necessary. If a user runs memory-intensive applications on a system with low physical memory, it is preferable to manually set these sizes to a value higher than default. Windows 95 is a consumer-oriented graphical user interface-based operating system. ...


Paging in Windows NT line

In NT-based versions of Windows (such as Windows 2000 and Windows XP), the file used for paging is named pagefile.sys. The default location of the page file is in the root directory of the partition where Windows is installed. Windows can be configured to use free space on any available drives for page files. Windows 2000 (also referred to as Win2K) is a preemptive, interruptible, graphical and business-oriented operating system designed to work with either uniprocessor or symmetric multi-processor computers. ... Windows XP is a line of operating systems developed by Microsoft for use on personal computers, including home and business desktops, notebook computers, and media centers. ...


Fragmentation of the page file

Occasionally, when the page file is gradually expanded, it can become heavily fragmented and cause performance problems. The common advice given to avoid this problem is to set a single "locked" page file size so that Windows will not resize it. However, the page file only expands when it has been filled, which, in its default configuration, is 150% the total amount of physical memory.[6] Thus the total demand for pagefile-backed virtual memory must exceed 250% of the computer's physical memory before the page file will expand. In computing, file system fragmentation, sometimes called file system aging, is the inability of a file system to lay out related data sequentially (contiguously), an inherent phenomenon in storage-backed file systems that allow in-place modification of their contents. ...


Locking a page file's size can be problematic in the case that a Windows application requests more memory than the total size of physical memory and the page file. In this case, requests to allocate memory fail, which may cause the programs making the request (including system processes) to fail. Supporters of this view will note that the page file is rarely read or written in sequential order, so the performance advantage of having a completely sequential page file is minimal. However, it is generally agreed that a large page file will allow use of memory-heavy applications, and there is no penalty except that more disk space is used.


Defragmenting the page file is also occasionally recommended to improve performance when a Windows system is chronically using much more memory than its total physical memory. Although this can help slightly, performance concerns are much more effectively dealt with by adding more physical memory. In the context of administering computer systems, defragmentation (or defragging) is a process that eliminates fragmentation in file systems. ...


Swapping in Linux

In Linux, as in most other Unix-like operating systems, it is common to use a whole partition of a hard disk for swapping. However, with the 2.6 Linux kernel, swap files are just as fast[7] as swap partitions, although Red Hat recommends using a swap partition.[8] The administrative flexibility of swap files outweighs that of partitions; since modern high capacity hard drives can remap physical sectors, no partition is guaranteed to be contiguous. This article is about operating systems that use the Linux kernel. ... Diagram of the relationships between several Unix-like systems A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification. ...


Linux supports using a virtually unlimited number of swapping devices, each of which can be assigned a priority. When the operating system needs to swap pages out of physical memory, it uses the highest-priority device with free space. If multiple devices are assigned the same priority, they are used in a fashion similar to level 0 RAID arrangements. This provides improved performance as long as the devices can be accessed efficiently in parallel. Therefore, care should be taken assigning the priorities. For example, swaps located on the same physical disk should not be used in parallel, but in order ranging from the fastest to the slowest (i.e.: the fastest having the highest priority). In computing, a redundant array of inexpensive disks, also later known as redundant array of independent disks (commonly abbreviated RAID) is a system which uses multiple hard drives to share or replicate data among the drives. ...


Recently, some experimental improvement to the 2.6 Linux kernel have been made by Con Kolivas, published in his popular -ck patchset[9]. The improvement, called "swap prefetch", employs a mechanism of prefetching previously swapped pages back to physical memory even before they are actually needed, as long as the system is relatively idle (so as not to impair performance) and there is available physical memory to use. This applies to a situation when a "heavy" application has been temporarily used, causing other processes to swap out. After it is closed, both freeing large areas of memory and reducing disk load, prefetch of other processes starts, reducing their initial user response time. [10] The Linux kernel is a Unix-like operating system kernel. ... Con Kolivas is practicing doctor in Australia but he is known for the work done on the Linux kernel in his spare time. ...


Tuning paging performance

The backing store for a virtual memory operating system is typically many orders of magnitude slower than RAM. Therefore it is desirable to reduce or eliminate swapping, where practical. Some operating systems offer settings to influence the kernel's decisions. The magnitude of a mathematical object is its size: a property by which it can be larger or smaller than other objects of the same kind; in technical terms, an ordering of the class of objects to which it belongs. ... RAM redirects here. ...

  1. Linux offers the /proc/sys/vm/swappiness parameter, which changes the balance between swapping out runtime memory, as opposed to dropping pages from the system page cache.
  2. Windows 2000, XP, and Vista offer the DisablePagingExecutive registry setting, which controls whether kernel-mode code and data can be eligible for paging out.

In AIX to improve performance you can use more than one device as paging space, since version AIX 4.3 these paging space devices can be added or removed without rebooting the system. AIX or Aix may be: Aix, a genus of two species of dabbling ducks, the Wood Duck (Aix sponsa) and the Mandarin Duck (Aix galericulata) AIX operating system Athens Internet Exchange, (AIX) a European IXP a place name: Aix-la-Chapelle, or Aachen, a city in Germany in France: Aix...


Tuning swap space size

In some older virtual memory operating systems, space in swap backing store is reserved when programs allocate memory for runtime data. OS vendors typically issue guidelines about how much swap space should be allocated. Between 1.5 or 2 times the installed RAM is a typical number [11]. With a large amount of RAM, the disk space needed for the backing store can be very large. Newer versions of these operating systems attempt to solve this problem: for example, some HP-UX kernels offer a tunable swapmem_on that controls whether RAM can be used for memory reservations. In systems with sufficient RAM, this significantly reduces the needed space allocation for the backing store. HP-UX (Hewlett Packard UniX) is Hewlett-Packards proprietary implementation of the Unix operating system, based on System V (initially System III). ...


See also

It has been suggested that this article or section be merged with Primary storage. ... This article is about the computer term. ... In computer operating systems, demand paging is an application of virtual memory. ... In computing, page cache, sometimes ambiguously called disk cache, is a transparent cache of disk-backed pages kept in primary storage (RAM) for quicker access. ... It has been suggested that this article or section be merged into cache algorithms. ... Segmentation is one of the most common ways to achieve memory protection; another common one is paging. ... Wikipedia does not yet have an article with this exact name. ... Relationship between pages addressed by virtual addresses and the frames in physical memory, within a simple address space scheme. ... It has been suggested that this article or section be merged with Dynamic memory allocation. ...

References

  1. ^ Belzer, Jack; Holzman, Albert G. & Kent, Allen, eds. (1981), "Virtual memory systems", Encyclopedia of computer science and technology, vol. 14, CRC Press, pp. 32, ISBN 0824722140, <http://books.google.com/books?id=KUgNGCJB4agC&printsec=frontcover> 
  2. ^ Deitel, Harvey M. (1983), An Introduction to Operating Systems, Addison-Wesley, pp. 181, 187, ISBN 0201144735 
  3. ^ Belzer, Jack; Holzman, Albert G. & Kent, Allen, eds. (1981), "Operating systems", Encyclopedia of computer science and technology, vol. 11, CRC Press, pp. 433, ISBN 0824722612, <http://books.google.com/books?id=uTFirmDlSL8C&printsec=frontcover> 
  4. ^ Belzer, Jack; Holzman, Albert G. & Kent, Allen, eds. (1981), "Operating systems", Encyclopedia of computer science and technology, vol. 11, CRC Press, pp. 442, ISBN 0824722612, <http://books.google.com/books?id=uTFirmDlSL8C&printsec=frontcover> 
  5. ^ Cragon, Harvey G. (1996), Memory Systems and Pipelined Processors, Jones and Bartlett Publishers, pp. 109, ISBN 0867204745, <http://books.google.com/books?id=q2w3JSFD7l4C> 
  6. ^ How to determine the appropriate page file size for 64-bit versions of Windows Server 2003 or Windows XP (MSKB889654_. Knowledge Base. Microsoft (November 7, 2007). Retrieved on 2007-12-26.
  7. ^ LKML: "Jesper Juhl": Re: How to send a break? - dump from frozen 64bit linux
  8. ^ http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/sysadmin-guide/ch-swapspace.html
  9. ^ http://kernel.kolivas.org Con Kolivas' 2.6 Linux Kernel patchset
  10. ^ http://ck.wikia.com/wiki/SwapPrefetch SwapPrefetch description on ck kernel wiki. Retrieved 18-09-2007.
  11. ^ http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manual/sysadmin-guide/ch-swapspace.html

is the 311th day of the year (312th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 360th day of the year (361st in leap years) in the Gregorian calendar. ...

External links

An operating system (OS) is a software that manages computer resources and provides programmers with an interface used to access those resources. ... A kernel connects the application software to the hardware of a computer. ... Graphical overview of a microkernel A microkernel is a minimal computer operating system kernel providing only basic operating system services (system calls), while other services (commonly provided by kernels) are provided by user-space programs called servers. ... It has been suggested that Monolithic system be merged into this article or section. ... Graphical overview of a hybrid kernel Hybrid kernel is a kernel architecture based on combining aspects of microkernel and monolithic kernel architectures used in computer operating systems. ... In computer engineering the kernel is the core of an operating system. ... In computing, loadable kernel modules, or LKM, are object files that contain code to extend the running kernel, or so-called base kernel, of an operating system. ... In computer science, a nanokernel or picokernel is a very minimalist operating system kernel. ... A device driver, or software driver is a computer program allowing higher-level computer programs to interact with a computer hardware device. ... An operating system usually segregates the available system memory into kernel space and user space. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... Process management is the ensemble of activities of planning and monitoring the performance of a process, especially in the sense of business process, often confused with reengineering. ... In computing, a process is an instance of a computer program that is being executed. ... In computing, multitasking is a method by which multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is... In computing, an interrupt is an asynchronous signal from hardware or software indicating the need for attention. ... Protected mode is an operational mode of x86-compatible CPUs of the 80286 series or later. ... In computer terms, supervisor mode is a hardware-mediated flag which can be changed by code running in system-level software. ... In computing, multitasking is a method by which multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is... For disk scheduling, see I/O scheduling. ... A context switch is the computing process of storing and restoring the state (context) of a CPU such that multiple processes can share a single CPU resource. ... In computing, cooperative multitasking (or non-preemptive multitasking) is a form of multitasking in which multiple tasks execute by voluntarily ceding control to other tasks at programmer-defined points within each task. ... Pre-emptive multitasking is a form of multitasking in which processes are not allowed to take an indefinitely long time to complete execution in the CPU. Each process, in turn, is granted a portion of CPU time (usually called a time slice, on the order of milliseconds). ... CPU modes (also called processor modes or privilege levels, and by other names) are operating modes for the central processing unit of some computers that place variable restrictions on the operations that can be performed by the CPU. Mode types At a minimum, any CPU with this type of architecture... Memory protection is a system that prevents one process from corrupting the memory of another process running on the same computer at the same time. ... Look up segmentation in Wiktionary, the free dictionary. ... This 68451 MMU could be used with the Motorola 68010 MMU, short for memory management unit or sometimes called paged memory management unit as PMMU, is a class of computer hardware components responsible for handling memory accesses requested by the CPU. Among the functions of such devices are the translation... It has been suggested that Access violation be merged into this article or section. ... A General Protection Fault (GPF) in the Intel x86 and AMD x86-64 architectures is a fault (a type of an interrupt) which can encompass several cases, where protection mechanisms within the processor architecture are violated by any of the programs that is running, whether it be the kernel or... AmigaOS is the default native operating system of the Amiga and AmigaOne personal computers. ... Filiation of Unix and Unix-like systems Unix (officially trademarked as UNIX®, sometimes also written as or ® with small caps) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. ... This article is about operating systems that use the Linux kernel. ... GNU (pronounced ) is a computer operating system composed entirely of free software. ... CP/M is an operating system originally created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc. ... MP/M was the multi-user version of the CP/M operating system, created by Digital Research. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Microsofts disk operating system, MS-DOS, was Microsofts implementation of DOS, which was the first popular operating system for the IBM PC, and until recently, was widely used on the PC compatible platform. ... Windows redirects here. ... This article relates to both the original Classic Mac OS as well as Mac OS X, Apples more recent operating system. ... In computing, Bootstrapping refers to a process where a simple system activates another more complicated system that serves the same purpose. ... API and Api redirect here. ... A virtual file system (VFS) or virtual filesystem switch is an abstraction layer on top of a more concrete file system. ... A computer network is an interconnection of a group of computers. ... GUI redirects here. ... The history of computer operating systems recapitulates to a degree, the recent history of computing. ... A hardware abstraction layer (HAL) is an abstraction layer, implemented in software, between the physical hardware of a computer and the software that runs on that computer. ...

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