141 g (for example, by killing the program).
1 astructure software component of a computer system; it is respons
46 lifies development of applications. Executing a program involves 
210 ionary power over where a particular application's memory is stor
122 upervisor mode. The first few programs to run on the computer, be
441 uch as a login at a connected console or some kind of network con
252 The philosophy governing preemptive multitasking is that of ensur
500  due to the number of programs which unnecessarily required admin
566 Many Linux distributions support some or all of ext2, ext3, ext4,
360  controlled differently. Computers and their operating systems ca
380 ctions. Networks can essentially allow a computer's operating sys
604 hem. Due to its UNIX heritage Mac OS X now supports virtually all
62 -- not a good use of CPU resources. Interrupt-based programming i
580 these file systems. Unlike other operating systems, Linux and UNI
156 tem of memory management is almost never seen anymore, since prog
344 e specific computer bus or communications subsystem that the hard
16 ams and users. Applications access these services through applica
190 emory when the Operating system is being installed on the system.
257 errupt. A protected mode timer is set by the kernel which trigger
184 MS-DOS applications ran in supervisor mode, giving them almost un
365 alls into device specific calls. In theory a new device, which is
244 An early model which governed the allocation of time to programs 
172  specify to the CPU what memory address it should allow a running
483 [edit] Example: Microsoft Windows
477 it allows each user of the system to have private files that the 
52 s intended function.
309  standard language used by the operating system to access all dis
322  creation and modification dates.
202 , the kernel will be interrupted in the same way as it would if t
143 [edit] Memory management
162 th cooperative memory management it takes only one misbehaved pro
356 The key design goal of device drivers is abstraction. Every model
269     Further information: Preemptive multitasking
591 lly limited in application to certain media, for example CDs must
442 nection. External requests are often passed through device driver
3 aring of the limited resources of the computer. The operating sys
333 l-purpose operating systems (for example, NTFS is available in Li
627  in the event of a system crash. A journaled file system writes s
501 istrator rights and so most home users ran as administrator all
24 ktop computers, the user interface is generally considered part o
666 l.
612 FAT file systems are commonly found on floppy disks, flash memory
677 m X11. Competition among the various vendors of Unix (HP, IBM, Su
589 he ISO 9660 and UDF filesystems used for CDs, DVDs, and other opt
160 rograms, or viruses may purposefully alter another program's memo
571 IX, Microsoft Windows, and other operating systems. Linux has ful
351 running under the operating system kernel, to interact transparen
315 d to translate the commands used to access each specific file sys
61 tch" the various sources of input for events that require action 
76 ware or from the running program.
258 s a return to supervisor mode after the specified time has elapse
325  systems difficult. Allowed characters in file names, case sensit
407 ork to provide sound from local applications, on a remote system'
399 puter by passing requests to the operating system kernel.
451 makers, because the TCSEC was used to evaluate, classify and sele
4 tem acts as a host for applications that are run on the machine. 
673  offer alternatives to the included Windows shell, but the shell 
79 's kernel decides how to deal with this event, generally by runni
60  environment. The alternative is to have the operating system "wa
403 DECnet on systems from Digital Equipment Corporation, and Microso
246 is passed to a program by the kernel, it may execute for as long 
124 access to hardware - and this is required because, by definition,
116  by a program running in supervisor mode. Similar modes have exis
495 m were nullified by the fact that, prior to Windows Vista, the fi
12 hat may be contained on a compact disk or other data storage devi
263 er of well tested programs. Windows NT was the first version of M
581 X allow any file system to be used regardless of the media it is 
417 stem, and to external devices like networks via the kernel.
575 In recent years support for Microsoft Windows NT's NTFS file syst
596 es.
129 In protected mode, programs may have access to a more limited set
215  to make that space available for use by other programs. This is 
412     Main article: computer security
480 tially bypass the operating system, inclusive of bypassing auditi
224     Main article: Computer multitasking
97 [edit] Protected mode and supervisor mode
361 nnot be expected to know how to control every device, both now an
532 s can also be locked down. This provides the user with plenty of 
553 [edit] File system support in modern operating systems
321 n about them, including access permissions, size, free space, and
619 rget Compact Discs and DVDs. Mount Rainier is a newer extension t
423 e a form of requester identity, such as a user name. To establish
341 A device driver is a specific type of computer software developed
671  Unix-like (BSD, GNU/Linux, Minix) systems. A number of Windows s
92 sed back to the kernel. The kernel will then process the request.
450 of security. This became of vital importance to operating system 
444  applications, or carried out directly. Security of operating sys
414 A computer being secure depends on a number of technologies worki
10 deo game consoles, use an operating system of some type. Some of 
364 e device driver is then to translate these OS mandated function c
576 em has appeared in Linux, and is now comparable to the support av
31 Common contemporary operating systems include Microsoft Windows, 
102 Modern CPUs support something called dual mode operation. CPUs wi
69 When an interrupt is received the computer's hardware automatical
498 h Windows XP did have limited accounts, the majority of home user
109 de as well, such as the virtual 8086 mode of the 80386 (Intel's x
108  to it. CPUs might have other modes similar to 80286 protected mo
646 [edit] Graphical user interfaces
110 86 32-bit microprocessor or i386).
85 operating system's kernel, part of another program, or both. Devi
556 systems although there are several common file systems which almo
504 Windows Vista changes this[3] by introducing a privilege elevatio
216 called swapping, as an area of memory can be used by multiple pro
259 d. (See above sections on Interrupts and Dual Mode Operation.)
517 , UAC will prompt for confirmation and, if consent is given (incl
446 d on computers, both of a commercial and military nature. The Uni
402 n networking protocols as well, for example, SNA on IBM systems, 
455 Network services include offerings such as file sharing, print se
544 t users to run programs as the root user via the sudo command, us
654 system service, incorporating support for one into the operating 
59 ficient way for the operating system to interact and react to its
562 em.
331 However, in practice, third party drives are usually available to
437 the operating system kernel. If programs can directly access hard
542 computer's root password when prompted. Some systems (such as Ubu
107 ocessor) CPU feature, although its protected mode is very similar
131 de only by triggering an interrupt, causing control to be passed 
572 l support for XFS and JFS, along with FAT (the MS-DOS file system
457  of which can have compromised security. At the front line of sec
324 Various differences between file systems make supporting all file
620 o UDF supported by Linux 2.6 kernels and Windows Vista that facil
443 s to the operating system's kernel, where they can be passed onto
568 . The ext file systems, namely ext2, ext3 and ext4 are based on t
80 ng some processing code. How much code gets run depends on the pr
43 The operating system acts as an interface between an application 
524 Linux and UNIX both have two tier security, which limits any syst
628 ome information twice: first to the journal, which is a log of fi
371 [edit] Networking
510  two separate tokens are assigned. The first token contains all p
373     Main article: Computer network
26  Unix-like systems, the user interface is generally implemented a
516 n requests higher privileges or "Run as administrator" is clicked
352 tly with a hardware device, and usually provides the requisite in
535 em-level bugs) or make sweeping, system-wide changes. The user's 
139 rally causes a switch to supervisor mode, where the operating sys
513 e. User applications, including the Windows Shell, are then start
168  some level of hardware support (such as the 80286 MMU) which doe
9 andheld computers, desktop computers, supercomputers, and even vi
421 should not be processed. While some systems may simply distinguis
183 could easily circumvent the need to use it. Under Windows 9x all 
530 lection of available programs, their total disk usage or quota, a
214  less frequently can be temporarily stored on disk or other media
330 em; for example, NTFS in Windows and extn and ReiserFS in Linux. 
48 ates a process by assigning memory and other resources, establish
279 , higher reliability, and to make better use out of the drive's a
28 (Whether the user interface should be included as part of the ope
166 o the computer's memory. Various methods of memory protection exi
363 how every type of device should be controlled. The function of th
66 d allow the programmer to specify code which may be run when that
661 his way. Modern releases of Microsoft Windows such as Windows Vis
265 idn't reach the home user market until Windows XP, (since Windows
346  from the device, and on the other end, the requisite interfaces 
195 The use of virtual memory addressing (such as paging or segmentat
494  lot of the advantages of being a true multi-user operating syste
127 r program, it can place the CPU into protected mode.
304  system drivers.
254 lies that all programs must be limited in how much time they are 
394  are usually provided through ports or numbered access points bey
424  identity there may be a process of authentication. Often a usern
622  with floppy disks.
182 Windows 3.1-Me had some level of memory protection, but programs 
151 time share, each program must have independent access to memory.
653 While technically a graphical user interface is not an operating 
538 n where the user may store their work, similar to My Documents on
186 ld be produced indicating a segmentation violation had occurred, 
232 the computer's time to execute.
54 [edit] Interrupts
155 emory manager, and do not exceed their allocated memory. This sys
90 If a program wishes to access hardware for example, it may interr
583 ed within a file located on another file system.
438 ware and resources, they cannot be secured.
425 ame must be quoted, and each username may have a password. Other 
470 An alternative strategy, and the only sandbox strategy available 
334 nux through NTFS-3g, and ext2/3 and ReiserFS are available in Win
678 n) led to much fragmentation, though an effort to standardize in 
358  Newer models also are released by manufacturers that provide mor
369  of view for any person.
428 from the network, resources may be accessed with no authenticatio
476 Internal security is especially relevant for multi-user systems; 
631 eeps track of each operation taking place that changes the conten
458 urity are hardware devices known as firewalls or intrusion detect
191  This part is known as swap space.
163 gram to crash the system.
492 The Windows NT series of operating systems, by contrast, are true
420 quests which should be allowed to be processed, and others which 
640 lternative to journaling that avoids the redundant writes by care
173  program to access. Attempts to access other addresses will trigg
460 a number of software firewalls available, as well as intrusion de
114 grams running in that mode, providing things like virtual memory 
241 ssing of control between the kernel and applications is called a 
132 back to the kernel. In this way the operating system can maintain
615 to most other file systems as it uses overly simplistic data stru
502  the time.
51 m then interacts with the user and/or other devices performing it
520 ocess using the unrestricted token.[4]
205 to as a page fault.
27 s an application program that runs outside the operating system. 
329 nd so support natively) file systems specifically designed for th
32 Mac OS, Linux, BSD and Solaris. Microsoft Windows has a significa
567  ReiserFS, Reiser4, JFS , XFS , GFS, GFS2, OCFS, OCFS2, and NILFS
525 em-wide changes to the root user, a special user account on all U
540  system-wide changes, they must become the root user temporarily,
255 allowed to spend on the CPU without being interrupted. To accompl
115 addressing and limiting access to hardware in a manner determined
83 ing of hardware interrupts is a task that is usually delegated to
551 vilege authorization features.
36 ing systems.
658 ing the graphics subsystem from the kernel and the Operating Syst
664 graphics drawing routines exist mostly in kernel space. Windows 9
367 ble driver is available. This new driver will ensure that the dev
154 ms assumes that all programs make voluntary use of the kernel's m
453 and retrieval of sensitive or classified information.
314 may contain one or more file systems. A file system driver is use
117 ted in supercomputers, minicomputers, and mainframes as they are 
47 the creation of a process by the operating system. The kernel cre
112 However, the term is used here more generally in operating system
459 ion/prevention systems. At the operating system level, there are 
228 er programs on the same computer, giving the appearance that it i
33 nt majority of market share in the desktop and notebook computer 
657 ts output functions. Other operating systems are modular, separat
598 [edit] Mac OS X
236 executing, and in which order execution control should be passed 
95 rnel's attention.
65 events. Even very basic computers support hardware interrupts, an
528 ser are limited in where they can save files, what hardware they 
91 upt the operating system's kernel, which causes control to be pas
656  the number of context switches required for the GUI to perform i
600 Mac OS X supports HFS+ with journaling as its primary file system
668 Many computer operating systems allow the user to install or crea
507 he most basic privileges is assigned. In this way, the new logon 
614 of their relative simplicity. Performance of FAT compares poorly 
180 he error.
289 reflected limitations in the operating systems they were designed
274     Main article: Virtual file system
564 [edit] Linux and UNIX
605  the file systems supported by the UNIX VFS. Recently Apple Inc. 
303 alled on them through the use of specific device drivers and file
354 pendent hardware interfacing needs.
405 ecific tasks may also be supported such as NFS for file access. P
427 ta, might be used instead. In some cases, especially connections 
280 vailable space. The specific way in which files are stored on a d
262  perfectly adequate, as home computers generally run a small numb
478 other users cannot tamper with or read. Internal security is also
176 violation or Seg-V for short, and since it is both difficult to a
256 ish this, modern operating system kernels make use of a timed int
659 em. In the 1980s UNIX, VMS and many others had operating systems 
287 limited in their capacity, speed, and in the kinds of file names 
359 e reliable or better performance and these newer models are often
384 ommunication, to using networked file systems or even sharing ano
174 er an interrupt which will cause the CPU to re-enter supervisor m
616 ctures, making file operations time-consuming, and makes poor use
545 ing the user's own password for authentication instead of the sys
295 ms like UNIX and Linux support a technology known as a virtual fi
670 tion with GNOME or KDE is a commonly-found setup on most Unix and
587 Microsoft Windows currently supports NTFS and FAT file systems, a
546 tem's root password. One is sometimes said to "go root" when elev
310 k drives. On UNIX this is the language of block devices.
189 In LINUX systems, part of the hard disk is reserved for virtual m
506 rd user, a logon session is created and a token containing only t
590 ical discs such as BluRay. Under Windows each file system is usua
140 tem can deal with the illegal operation the program was attemptin
663 owever versions between Windows NT 4.0 and Windows Server 2003's 
306 A connected storage device such as a hard drive is accessed throu
211 ed, or even whether or not it has actually been allocated yet.
204 emory management.) Under UNIX this kind of interrupt is referred 
638 ined in their entirety by a utility such as fsck or chkdsk for an
550  approach and Vista's User Account Control, see Comparison of pri
291  more than one file system.
19 perating system, pass parameters, and receive the results of the 
440 External security involves a request from outside the computer, s
617  of disk space in situations where many small files are present. 
35 systems. Embedded device markets are split amongst several operat
87 ious means.
641 fully ordering the update operations. Log-structured file systems
318 se file systems on the basis of filenames, and directories/folder
493  multi-user, and implement absolute memory protection. However, a
431 In addition to the allow/disallow model of security, a system wit
296 le system or VFS. A modern operating system like UNIX supports a 
385 ther computer's graphics or sound hardware. Some network services
375 Currently most operating systems support a variety of networking 
432 h a high level of security will also offer auditing options. Thes
349  system specific that enables another program, typically an opera
471 in systems that do not meet the Popek and Goldberg virtualization
313  then access the contents of the disk drive in raw format, which 
514 ed with the restricted token, resulting in a reduced privilege en
270     Further information: Cooperative multitasking
608 .
149 ly in use by programs. This ensures that a program does not inter
419 The operating system must be capable of distinguishing between re
387 such as SSH which allows networked users direct access to a compu
209  it access to the memory requested. This gives the kernel discret
353 terrupt handling necessary for any necessary asynchronous time-de
388 ter's command line interface.
406 rotocols like ESound, or esd can be easily extended over the netw
485 While the Windows 9x series offered the option of having profiles
490 k of security.
300 ny knowledge about the device they are accessing. A VFS allows th
197 y use at any given time, allowing the operating system to use the
159 or more other programs to be affected or overwritten. Malicious p
316 tem into a standard set of commands that the operating system can
487 d did not allow concurrent access; and so were not true multi-use
416 r of resources, which are available to software running on the sy
350 ting system or applications software package or computer program 
603  read), UDF, and other file systems, but cannot be installed to t
203 he program were to exceed its allocated memory. (See section on m
396 ociated with a maximum of one running program, which is responsib
234 An operating system kernel contains a piece of software called a 
171 In both segmentation and paging, certain protected mode registers
6 e the details of the operation of the hardware. This relieves app
21  some kind of software user interface (UI) like typing commands b
512 s a restricted token similar to what a standard user would receiv
50 g program code into memory, and executing the program. The progra
397 le for handling requests to that port. A daemon, being a user pro
148 st be responsible for managing all system memory which is current
362 d in the future. To solve this problem, OSes essentially dictate 
395 ond the server's network address. Each port number is usually ass
332  give support for the most widely used filesystems in most genera
125  initializing a protected environment can only be done outside of
343 itutes an interface for communicating with the device, through th
606 started work on porting Sun Microsystem's ZFS filesystem to Mac O
594 s Embedded CE 6.0, Windows Vista Service Pack 1, and Windows Serv
5 As a host, one of the purposes of an operating system is to handl
229 s performing the tasks at the same time. Since most computers can
145     Main article: memory protection
82 o a smoke detector alarm before answering the phone). The process
376 protocols, hardware, and applications for using them. This means 
522 [edit] Example: Linux/Unix
391 re which connects via a network to another computer, called a ser
100     Main article: Supervisor mode
245 was called cooperative multitasking. In this model, when control 
434 as, "who has been reading this file?"). Internal security, or sec
113  theory to refer to all modes which limit the capabilities of pro
8 t easier to write applications. Almost all computers, including h
178  usually a sign of a misbehaving program, the kernel will general
121 When a computer first starts up, it is automatically running in s
377 that computers running dissimilar operating systems can participa
288 and directory structures they could use. These limitations often 
133  exclusive control over things like access to hardware and memory
536 settings are stored in an area of the computer's file system call
588 long with network file systems shared from other computers, and t
383 tly to the local computer. This includes everything from simple c
67  event takes place.
585 [edit] Microsoft Windows
200 If a program tries to access memory that isn't in its current ran
408 s sound hardware.
613  cards, digital cameras, and many other portable devices because 
422 h between "privileged" and "non-privileged", systems commonly hav
285 Early operating systems generally supported a single type of disk
526 NIX-like systems. While the root user has virtually unlimited per
179 ly resort to terminating the offending program, and will report t
462  a software firewall, which is enabled by default. A software fir
685 Graphical user interfaces evolve over time. For example, Windows 
486  for multiple users, they had no concept of access privileges, an
72 pt. This is analogous to placing a bookmark in a book when someon
235 scheduler which determines how much time each program will spend 
379 iles, printers, and scanners using either wired or wireless conne
93  If a program wishes additional resources (or wishes to shed reso
415 ng properly. A modern operating system provides access to a numbe
601 . It is derived from the Hierarchical File System of the earlier 
217 grams, and what that memory area contains can be swapped or excha
34 markets, while servers generally run on Linux or other Unix-like 
342  to allow interaction with hardware devices. Typically this const
23 terface (GUI, commonly pronounced “gooey”). For hand-held and des
665 x had very little distinction between the interface and the kerne
561 It supports the file system ZFS, commonly known as Zeta Byte Syst
268     Further information: Context switch
473 as native code, but instead either emulates a processor or provid
573 ), and HFS which is the primary file system for the Macintosh.
537 ed the user's home directory, which is also provided as a locatio
557 st all operating systems include support and drivers for.
515 vironment even under an Administrator account. When an applicatio
39 Program execution
106 s not refer specifically to the 80286 (Intel's x86 16-bit micropr
435 urity from an already running program is only possible if all pos
635  Ext3.
201 ge of accessible memory, but nonetheless has been allocated to it
577 ailable for other native UNIX file systems. ISO 9660 and UDF are 
44 and the hardware. The user interacts with the hardware from "the 
529 can access, etc. In many systems, a user's memory usage, their se
488 r operating systems. In addition, they implemented only partial m
277 ting systems. Computers store data on disks using files, which ar
474 es a host for a p-code based system such as Java.
607 S X and preliminary support is already available in Mac OS X 10.5
196 ion) means that the kernel can choose what memory each program ma
634 UNIX file systems provide journaling including ReiserFS, JFS, and
448 sted Computer System Evaluation Criteria (TCSEC) which is a stand
449 ard that sets basic requirements for assessing the effectiveness 
679 the 1990s to COSE and CDE failed for the most part due to various
452 ct computer systems being considered for the processing, storage 
320 lete, open, and close files, as well as gather various informatio
0 An operating system (commonly abbreviated OS and O/S) is the infr
272 [edit] Disk access and file systems
264 icrosoft Windows which enforced preemptive multitasking, but it d
185 limited control over the computer. A general protection fault wou
534  of the system in jeopardy (barring accidental triggering of syst
461 tection/prevention systems. Most modern operating systems include
283 rectories or folders arranged in a directory tree.
17 tion programming interfaces (APIs) or system calls. By invoking t
527 mission to affect system changes, programs running as a regular u
468 to the service on that port.
74 ern operating systems interrupts are handled by the operating sys
337 [edit] Device drivers
293 While many simpler operating systems support a limited range of o
312 When the kernel has an appropriate device driver in place, it can
282 attributes. It also allows them to be stored in a hierarchy of di
639 y inconsistencies after an unclean shutdown. Soft updates is an a
175 ode, placing the kernel in charge. This is called a segmentation 
58 Interrupts are central to operating systems as they provide an ef
479  vital if auditing is to be of any use, since a program can poten
250 e entire system if it enters an infinite loop.
238 allows the program access to the CPU and memory. At a later time 
126  one. However, when the operating system passes control to anothe
582 stored on, whether it is a hard drive, CD or DVD, or even contain
301 e operating system to provide programs with access to an unlimite
327  the implementation of a single interface for every file system a
378 te in a common network for sharing resources such as computing, f
136 The term "protected mode resource" generally refers to one or mor
153 Cooperative memory management, used by many early operating syste
592  use ISO 9660 or UDF, and as of Windows Vista, NTFS is the only f
509 re system. When logging in as a user in the Administrators group,
681  and KDE. Prior to open source-based toolkits and desktop environ
481 ng.
193 [edit] Virtual memory
299 interface (API). This makes it unnecessary for programs to have a
518 uding administrator credentials if the account requesting the ele
335 dows through FS-driver and rfstool).
505 n system called User Account Control. When logging in as a standa
511 rivileges typically awarded to an administrator, and the second i
86 ce drivers may then relay information to a running program by var
508 session is incapable of making changes that would affect the enti
651 he GUI is integrated into the kernel.
497 rator account, which was also the default for new accounts. Thoug
75 tem's kernel. Interrupts may come from either the computer's hard
161 ry or may affect the operation of the operating system itself. Wi
123 ing the BIOS, bootloader and the operating system have unlimited 
177 ssign a meaningful result to such an operation, and because it is
433 e would allow tracking of requests for access to resources (such 
559 [edit] Solaris
543 ntu and its derivatives) are configured by default to allow selec
426 methods of authentication, such as magnetic cards or biometric da
610 [edit] Special-purpose file systems
472  requirements, is the operating system not running user programs 
167 st, including memory segmentation and paging. All methods require
466 s Telnet or FTP, and not have to be threatened by a security brea
404 ft-specific protocols (SMB) on Windows. Specific protocols for sp
25 f the operating system. On large multi-user systems like Unix and
307 gh a device driver. The device driver understands the specific la
18 hese interfaces, the application can request a service from the o
649 UI), and often include them. In some computer systems, such as th
366  controlled in a new manner, should function correctly if a suita
2 ible for the management and coordination of activities and the sh
393 ous services to other network computers and users. These services
138 am isn't allowed to alter. Attempts to alter these resources gene
465 efore, one can install and be running an insecure service, such a
531 vailable range of programs' priority settings, and other function
328  daunting task. Operating systems tend to recommend the use of (a
392 ver. Servers, usually running UNIX or Linux, offer (or host) vari
134 .
11 the oldest models may however use an embedded operating system, t
629 le system operations, then to its proper place in the ordinary fi
207 When the kernel detects a page fault it will generally adjust the
602 Mac OS. Mac OS X has facilities to read and write FAT, NTFS (only
499 s did not change to an account type with fewer rights – partially
213 In modern operating systems, application memory which is accessed
240  another program may be allowed to use the CPU. This so-called pa
674 itself cannot be separated from Windows.
290  for, making it very difficult for an operating system to support
298  systems to be accessed through a common application programming 
187 however the system would often crash anyway.
579 BluRay discs. It is possible to install Linux on the majority of 
227 Multitasking refers to the running of multiple independent comput
463 ewall can be configured to allow or deny network traffic to or fr
119 ems.
71 us, and runs computer code previously associated with the interru
555 Support for file systems is highly varied among modern operating 
225     Main article: Process management (computing)
137 e CPU registers, which contain information that the running progr
230  do at most one or two things at one time, this is generally done
147 Among other things, a multiprogramming operating system kernel mu
618 ISO 9660 and Universal Disk Format are two common formats that ta
278 e structured in specific ways in order to allow for faster access
89 A program may also trigger an interrupt to the operating system. 
496 rst user account created during the setup process was an administ
410 [edit] Security
445 tems has long been a concern because of highly sensitive data hel
198  same memory locations for multiple tasks.
569 he original Linux file system. Others have been developed by comp
398 gram, can in turn access the local hardware resources of that com
15 Operating systems offer a number of services to application progr
447 ted States Government Department of Defense (DoD) created the Tru
218 nged on demand.
70 ly suspends whatever program is currently running, saves its stat
104 ode, which allow certain CPU functions to be controlled and affec
317  use to talk to all file systems. Programs can then deal with the
436 sibly harmful requests must be carried out through interrupts to 
13 ce.
118 essential to fully supporting UNIX-like multi-user operating syst
549 For more information on the differences between the Linux su/sudo
41     Main article: Process (computing)
643 hat they avoid inconsistencies by always writing new copies of th
94 urces) such as memory, it will trigger an interrupt to get the ke
308 nguage of the drive and is able to translate that language into a
429 n at all (such as reading files over a network share).
49 ing a priority for the process (in multi-tasking systems), loadin
297 wide array of storage devices, regardless of their design or file
165 Memory protection enables the kernel to limit a process' access t
456 rvices, email, web sites, and file transfer protocols (FTP), most
687 sion of Windows is released, and the Mac OS GUI changed dramatica
56     Main article: interrupt
105 ted only by the operating system kernel. Here, protected mode doe
347 to the operating system and software applications. It is a specia
99     Main article: Protected mode
266  NT was targeted at professionals.)
169 sn't exist in all computers.
45 other side". The operating system is a set of services which simp
286  drive and only one kind of file system. Early file systems were 
467 ch because the firewall would deny all traffic trying to connect 
655 system kernel can allow the GUI to be more responsive by reducing
624 [edit] Journalized file systems
73 e is interrupted by a phone call and then taking the call. In mod
319 s, contained within a hierarchical structure. They can create, de
686 has modified its user interface almost every time a new major ver
249 prevent any other programs from using the CPU, but it can hang th
281 isk is called a file system, and enables files to have names and 
519 vation is not a member of the administrators group), start the pr
237 to programs. Control is passed to a process by the kernel, which 
7 lication programs from having to manage these details and makes i
669 te any user interface they desire. The X Window System in conjunc
390 Client/server networking involves a program on a computer somewhe
489 emory protection. They were accordingly widely criticised for lac
261 On many single user operating systems cooperative multitasking is
247 as it wants before explicitly returning control to the kernel. Th
150 fere with memory already used by another program. Since programs 
357  of hardware (even within the same class of device) is different.
688 lly with the introduction of Mac OS X in 2001.
690 Reference: Wikipedia.org
63 s directly supported by most CPUs. Interrupts provide a computer 
81 iority of the interrupt (for example: a person usually responds t
326 ivity, and the presence of various kinds of file attributes makes
130  of the CPU's instructions. A user program may leave protected mo
253 ing that all programs are given regular time on the CPU. This imp
208  virtual memory range of the program which triggered it, granting
539  a Windows system. Should a user have to install software or make
672 hell replacements have been released for Microsoft Windows, which
29 rating system is a point of contention.)
339     Main article: Device driver
541  usually with the su or sudo command, which is answered with the 
276 Access to files stored on disks is a central feature of all opera
345 ware is connected to, providing commands to and/or receiving data
637 In contrast, non-journaled file systems typically need to be exam
630 le system. Journaling is handled by the file system driver, and k
401 Many operating systems support one or more vendor-specific or ope
578 supported which are standard file systems used on CDs, DVDs, and 
242 context switch.
642  and ZFS also differ from traditional journaled file systems in t
157 rams often contain bugs which can cause them to exceed their allo
248 is means that a malicious or malfunctioning program may not only 
644 e data, eschewing in-place updates.
239 control is returned to the kernel through some mechanism, so that
302 d number of devices with an infinite variety of file systems inst
648 Most modern computer systems support graphical user interfaces (G
20 operation. Users may also interact with the operating system with
650 e original implementations of Microsoft Windows and the Mac OS, t
220     Further information: Page fault
593 ile system which the operating system can be installed on. Window
22 y using command line interface (CLI) or using a graphical user in
626 File systems may provide journaling, which provides safe recovery
368 ice appears to operate as usual from the operating systems' point
547 ating oneself to root access.
660 that were built this way. GNU/Linux and Mac OS X are also built t
682 ments, Motif was the prevalent toolkit/desktop combination (and w
84  software called device drivers, which may be either part of the 
64 with a way of automatically running specific code in response to 
621 itates rewriting to DVDs in the same fashion as has been possible
386  allow the resources of a computer to be accessed transparently, 
676 Numerous Unix-based GUIs have existed over time, most derived fro
78 When a hardware device triggers an interrupt the operating system
633 o a consistent state by replaying a portion of the journal. Many 
464 om a service or application running on the operating system. Ther
382 ame functions as it could if those resources were connected direc
348 lized hardware-dependent computer program which is also operating
533 freedom to do what needs done, without being able to put any part
294 ptions for accessing storage systems, more modern operating syste
683 as the basis upon which CDE was developed).
103 th this capability use two modes: protected mode and supervisor m
222 [edit] Multitasking
680  reasons, eventually eclipsed by the widespread adoption of GNOME
381 tem to access the resources of a remote computer to support the s
595 er 2008 support ExFAT, a file system more suitable for flash driv
231  via time sharing, which means that each program uses a share of 
632 ts of the disk. In the event of a crash, the system can recover t
570 anies to meet their specific needs, hobbyists, or adapted from UN
662 ta implement a graphics subsystem that is mostly in user-space, h
158 cated memory. If a program fails it may cause memory used by one