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Text of the page (random words):
bs receive more processor time than those considered less significant depending on the operating system a task might be as large as an entire application program or might be made up of smaller threads that carry out portions of the overall program a processor intended for use with multitasking operating systems may include special hardware to securely support multiple tasks such as memory protection and protection rings that ensure the supervisory software cannot be damaged or subverted by user mode program errors the term multitasking has become an international term as the same word is used in many other languages such as german italian dutch romanian czech danish and norwegian contents 1 multiprogramming 2 cooperative multitasking 3 preemptive multitasking 4 real time 5 multithreading 6 memory protection 7 memory swapping 8 programming 9 see also 10 references multiprogramming edit in the early days of computing cpu time was expensive and peripherals were very slow when the computer ran a program that needed access to a peripheral the central processing unit cpu would have to stop executing program instructions while the peripheral processed the data this was usually very inefficient the first computer using a multiprogramming system was the british leo iii owned by j lyons and co during batch processing several different programs were loaded in the computer memory and the first one began to run when the first program reached an instruction waiting for a peripheral the context of this program was stored away and the second program in memory was given a chance to run the process continued until all programs finished running 3 the use of multiprogramming was enhanced by the arrival of virtual memory and virtual machine technology which enabled individual programs to make use of memory and operating system resources as if other concurrently running programs were for all practical purposes nonexistent citation needed multiprogramming gives no guarantee that a program will run in a timely manner indeed the first program may very well run for hours without needing access to a peripheral as there were no users waiting at an interactive terminal this was no problem users handed in a deck of punched cards to an operator and came back a few hours later for printed results multiprogramming greatly reduced wait times when multiple batches were being processed 4 5 cooperative multitasking edit main article cooperative multitasking early multitasking systems used applications that voluntarily ceded time to one another this approach which was eventually supported by many computer operating systems is known today as cooperative multitasking although it is now rarely used in larger systems except for specific applications such as cics or the jes2 subsystem cooperative multitasking was once the only scheduling scheme employed by microsoft windows and classic mac os to enable multiple applications to run simultaneously cooperative multitasking is still used today on risc os systems 6 as a cooperatively multitasked system relies on each process regularly giving up time to other processes on the system one poorly designed program can consume all of the cpu time for itself either by performing extensive calculations or by busy waiting both would cause the whole system to hang in a server environment this is a hazard that makes the entire environment unacceptably fragile preemptive multitasking edit main article preemption computing preemptive multitasking kubuntu kde plasma 5 four virtual desktops running multiple programs at the same time preemptive multitasking allows the computer system to more reliably guarantee to each process a regular slice of operating time it also allows the system to deal rapidly with important external events like incoming data which might require the immediate attention of one or another process operating systems were developed to take advantage of these hardware capabilities and run multiple processes preemptively preemptive multitasking was implemented in the pdp 6 monitor and multics in 1964 in os 360 mft in 1967 and in unix in 1969 and was available in some operating systems for computers as small as dec s pdp 8 it is a core feature of all unix like operating systems such as linux solaris and bsd with its derivatives 7 as well as modern versions of windows at any specific time processes can be grouped into two categories those that are waiting for input or output called i o bound and those that are fully utilizing the cpu cpu bound in primitive systems the software would often poll or busywait while waiting for requested input such as disk keyboard or network input during this time the system was not performing useful work with the advent of interrupts and preemptive multitasking i o bound processes could be blocked or put on hold pending the arrival of the necessary data allowing other processes to utilize the cpu as the arrival of the requested data would generate an interrupt blocked processes could be guaranteed a timely return to execution citation needed the earliest preemptive multitasking os available to home users was sinclair qdos on the sinclair ql released in 1984 but very few people bought the machine commodore s amiga released the following year was the first commercially successful home computer to use the technology and its multimedia abilities make it a clear ancestor of contemporary multitasking personal computers microsoft made preemptive multitasking a core feature of their flagship operating system in the early 1990s when developing windows nt 3 1 and then windows 95 it was later adopted on the apple macintosh by mac os x that as a unix like operating system uses preemptive multitasking for all native applications a similar model is used in windows 9x and the windows nt family where native 32 bit applications are multitasked preemptively 8 64 bit editions of windows both for the x86 64 and itanium architectures no longer support legacy 16 bit applications and thus provide preemptive multitasking for all supported applications real time edit another reason for multitasking was in the design of real time computing systems where there are a number of possibly unrelated external activities needed to be controlled by a single processor system in such systems a hierarchical interrupt system is coupled with process prioritization to ensure that key activities were given a greater share of available process time 9 multithreading edit as multitasking greatly improved the throughput of computers programmers started to implement applications as sets of cooperating processes e g one process gathering input data one process processing input data one process writing out results on disk this however required some tools to allow processes to efficiently exchange data citation needed threads were born from the idea that the most efficient way for cooperating processes to exchange data would be to share their entire memory space thus threads are effectively processes that run in the same memory context and share other resources with their parent processes such as open files threads are described as lightweight processes because switching between threads does not involve changing the memory context 10 11 12 while threads are scheduled preemptively some operating systems provide a variant to threads named fibers that are scheduled cooperatively on operating systems that do not provide fibers an application may implement its own fibers using repeated calls to worker functions fibers are even more lightweight than threads and somewhat easier to program with although they tend to lose some or all of the benefits of threads on machines with multiple processors 13 some systems directly support multithreading in hardware memory protection edit main article memory protection essential to any multitasking system is to safely and effectively share access to system resources access to memory must be strictly managed to ensure that no process can inadvertently or deliberately read or write to memory locations outside the process s address space this is done for the purpose of general system stability and data integrity as well as data security in general memory access management is a responsibility of the operating system kernel in combination with hardware mechanisms that provide supporting functionalities such as a memory management unit mmu if a process attempts to access a memory location outside its memory space the mmu denies the request and signals the kernel to take appropriate actions this usually results in forcibly terminating the offending process depending on the software and kernel design and the specific error in question the user may receive an access violation error message such as segmentation fault in a well designed and correctly implemented multitasking system a given process can never directly access memory that belongs to another process an exception to this rule is in the case of shared memory for example in the system v inter process communication mechanism the kernel allocates memory to be mutually shared by multiple processes such features are often used by database management software such as postgresql inadequate memory protection mechanisms either due to flaws in their design or poor implementations allow for security vulnerabilities that may be potentially exploited by malicious software memory swapping edit use of a swap file or swap partition is a way for the operating system to provide more memory than is physically available by keeping portions of the primary memory in secondary storage while multitasking and memory swapping are two completely unrelated techniques they are very often used together as swapping memory allows more tasks to be loaded at the same time typically a multitasking system allows another process to run when the running process hits a point where it has to wait for some portion of memory to be reloaded from secondary storage 14 programming edit processes that are entirely independent are not much trouble to program in a multitasking environment most of the complexity in multitasking systems comes from the need to share computer resources between tasks and to synchronize the operation of co operating tasks citation needed various concurrent computing techniques are used to avoid potential problems caused by multiple tasks attempting to access the same resource citation needed bigger systems were sometimes built with a central processor s and some number of i o processors a kind of asymmetric multiprocessing citation needed over the years multitasking systems have been refined modern operating systems generally include detailed mechanisms for prioritizing processes while symmetric multiprocessing has introduced new complexities and capabilities 15 see also edit process state task switching references edit concurrency vs parallelism concurrent programming vs parallel programming oracle archived from the original on april 7 2016 retrieved march 23 2016 anthony ralston edwin d reilly ed encyclopedia of computer science third edition van nostrand reinhold 1993 isbn 0 442 27679 6 articles multitasking and multiprogramming master programe and programme trials system part 1 master programme specification february 1965 section 6 priority control routines lithmee 2019 05 20 what is the difference between batch processing and multiprogramming pediaa com retrieved 2020 04 14 evolution of operating system 2017 09 29 retrieved 2020 04 14 preemptive multitasking riscos info 2009 11 03 retrieved 2014 07 27 unix part one the digital research initiative ibiblio org 2002 01 30 retrieved 2014 01 09 joseph moran june 2006 windows 2000 16 bit applications smart computing vol 16 no 6 pp 32 33 archived from the original on january 25 2009 liu c l layland james w 1973 01 01 scheduling algorithms for multiprogramming in a hard real time environment journal of the acm 20 1 46 61 doi 10 1145 321738 321743 issn 0004 5411 eduardo ciliendo takechika kunimasa april 25 2008 linux performance and tuning guidelines pdf redbooks ibm com ibm p 4 archived from the original pdf on february 26 2015 retrieved march 1 2015 context switch definition linfo org may 28 2006 archived from the original on february 18 2010 retrieved february 26 2015 what are threads user kernel tldp org september 8 1997 retrieved february 26 2015 multitasking different methods accessed on february 19 2019 what is a swap file kb iu edu retrieved 2018 03 26 operating systems architecture cis2 oc ctc edu retrieved 2018 03 17 v t e operating systems general comparison forensic engineering history list timeline usage share user features comparison variants disk operating system distributed operating system embedded operating system hobbyist operating system just enough operating system mobile operating system network operating system object oriented operating system real time operating system supercomputer operating system kernel architectures exokernel hybrid microkernel monolithic multikernel vkernel rump kernel unikernel components device driver loadable kernel module user space and kernel space process management concepts computer multitasking cooperative preemptive context switch interrupt ipc process process control block real time thread time sharing scheduling algorithms fixed priority preemptive multilevel feedback queue round robin shortest job next memory management resource protection bus error general protection fault memory paging memory protection protection ring segmentation fault virtual memory storage access file systems boot loader defragmentation device file file attribute inode journal partition virtual file system virtual tape library supporting concepts api computer network hal live cd live usb shell cli user interface pxe v t e parallel computing general distributed computing parallel computing massively parallel cloud computing high performance computing multiprocessing manycore processor gpgpu computer network systolic array levels bit instruction thread task data memory loop pipeline multithreading temporal simultaneous smt speculative spmt preemptive cooperative clustered multi thread cmt hardware scout theory pram model pem model analysis of parallel algorithms amdahl s law gustafson s law cost efficiency karp flatt metric slowdown speedup elements process thread fiber instruction window array coordination multiprocessing memory coherence cache coherence cache invalidation barrier synchronization application checkpointing programming stream processing dataflow programming models implicit parallelism explicit parallelism concurrency non blocking algorithm hardware flynn s taxonomy sisd simd array processing simt pipelined processing associative processing misd mimd dataflow architecture pipelined processor superscalar processor vector processor multiprocessor symmetric asymmetric memory shared distributed distributed shared uma numa coma massively parallel computer computer cluster beowulf clust...