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Computeroperating systems (OSes) provide a set of functions needed and used by most application programs on a computer, and the links needed to control and synchronize computer hardware. On the first computers, with no operating system, every program needed the full hardware specification to run correctly and perform standard tasks, and its own drivers forperipheral devices like printers andpunched paper card readers. The growing complexity of hardware and application programs eventually made operating systems a necessity for everyday use.
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Early computers lacked any form of operating system. Instead, the user, also called the operator, had sole use of the machine for a scheduled period of time. The operator would arrive at the computer with program and data which needed to be loaded into the machine before the program could be run. Loading of program and data was accomplished in various ways including toggle switches,punched paper cards and magnetic or paper tape.[1][2][3] Once loaded, the machine would be set to execute the single program until that program completed or crashed. Programs could generally be debugged via a control panel using dials, toggle switches and panel lights, making it a very manual and error-prone process.[4]
Symbolic languages,assemblers,[5][6][7]compilers were developed for programmers to translate symbolic program code intomachine code that previously would have been hand-encoded. Later machines came withlibraries of support code on punched cards or magnetic tape, which would be linked to the user's program to assist in operations such as input and output. This was the genesis of the modern-day operating system; however, machines still ran a single program or job at a time. AtCambridge University in England thejob queue was at one time a string from which tapes attached to corresponding job tickets were hung with stationery pegs.[8]
As machines became more powerful the time to run programs diminished, and the time to hand off the equipment to the next user became large by comparison. Accounting for and paying for machine usage moved on from checking the wall clock to automatic logging by the computer. Run queues evolved from a literal queue of people at the door, to a heap of media on a jobs-waiting table, or batches of punched cards stacked one on top of the other in the reader, until the machine itself was able to select and sequence whichmagnetic tape drives processed which tapes. Where program developers had originally had access to run their own jobs on the machine, they were supplanted by dedicated machine operators who looked after the machine and were less and less concerned with implementing tasks manually. When commercially available computer centers were faced with the implications of data lost through tampering or operational errors, equipment vendors were put under pressure to enhance the runtime libraries to prevent misuse of system resources. Automated monitoring was needed not just forCPU usage but for counting pages printed, cards punched, cards read, disk storage used and for signaling when operator intervention was required by jobs such as changing magnetic tapes and paper forms. Security features were added to operating systems to recordaudit trails of which programs were accessing which files and to prevent access to a production payroll file by an engineering program, for example.
All these features were building up towards the repertoire of a fully capable operating system. Eventually theruntime libraries became an amalgamated program that was started before the first customer job and could read in the customer job, control its execution, record its usage, reassign hardware resources after the job ended, and immediately go on to process the next job. These resident background programs, capable of managing multi step processes, were often calledmonitors or monitor-programs before the term "operating system" established itself.
An underlying program offering basic hardware management, software scheduling and resource monitoring may seem a remote ancestor to the user-oriented OSes of thepersonal computing era. But there has been a shift in the meaning of OS. Just as early automobiles lacked speedometers, radios, and air conditioners which later became standard, more and more optional software features became standard in every OS package. This has led to the perception of an OS as a complete user system with an integratedgraphical user interface, utilities, and some applications such asfile managers,text editors, and configuration tools.
The true descendant of the early operating systems is what is now called the "kernel". In technical and development circles the old restricted sense of an OS persists because of the continued active development ofembedded operating systems for all kinds of devices with a data-processing component, from hand-held gadgets up to industrial robots andreal-time control systems, which do not run user applications at the front end. An embedded OS in a device today is not so far removed as one might think from its ancestor of the 1950s.
The broader categories of systems and application software are discussed in thecomputer software article.
The first operating system used for real work wasGM-NAA I/O, produced in 1956 byGeneral Motors' Research division[9] for itsIBM 704.[10][specify] Most other early operating systems for IBM mainframes were also produced by customers.[11]
Early operating systems were very diverse, with each vendor or customer producing one or more operating systems specific to their particularmainframe computer. Every operating system, even from the same vendor, could have radically different models of commands, operating procedures, and such facilities as debugging aids. Typically, each time the manufacturer brought out a new machine, there would be a new operating system, and most applications would have to be manually adjusted, recompiled, and retested.
Building on customer experience and requirements, IBM took on a more active role in developing operating systems for the709,1410,7010,7040,7044,7090 and7094. IBM also collaborated with universities.
The state of affairs continued until the mid 1960s whenIBM, already a leading hardware vendor, stopped work on existing systems and put all its effort into developing theSystem/360 series of machines, all of which used thesame instruction and input/output architecture. IBM intended to develop a single operating system for the new hardware, theOS/360. The problems encountered in the development of the OS/360 are legendary, and are described byFred Brooks inThe Mythical Man-Month—a book that has become a classic ofsoftware engineering. Because of performance differences across the hardware range and delays with software development, a whole family of operating systems was introduced instead of a single OS/360.[12][13]
IBM wound up releasing a series of stop-gaps followed by two longer-lived operating systems:
IBM maintained full compatibility with the past, so that programs developed in the sixties can still run under z/VSE (if developed for DOS/360) or z/OS (if developed for MFT or MVT) with no change.
IBM also developedTSS/360, a time-sharing system for theSystem/360 Model 67. Overcompensating for their perceived importance of developing a timeshare system, they set hundreds of developers to work on the project. Early releases of TSS were slow and unreliable; by the time TSS had acceptable performance and reliability, IBM wanted its TSS users to migrate to OS/360 and OS/VS2; while IBM offered a TSS/370 PRPQ, they dropped it after 3 releases.[14]
Several operating systems for the IBM S/360 and S/370 architectures were developed by third parties, including theMichigan Terminal System (MTS) andMUSIC/SP.
Control Data Corporation developed theSCOPE operating systems[NB 1] in the 1960s, forbatch processing and later developed theMACE operating system for time sharing, which was the basis for the laterKronos. In cooperation with theUniversity of Minnesota, the Kronos and later theNOS operating systems were developed during the 1970s, which supported simultaneous batch and time sharing use. Like many commercial time sharing systems, its interface was an extension of theDTSS time sharing system, one of the pioneering efforts in timesharing and programming languages.
In the late 1970s, Control Data and theUniversity of Illinois developed thePLATO system, which used plasma panel displays and long-distance time sharing networks. PLATO was remarkably innovative for its time; the shared memory model of PLATO'sTUTOR programming language allowed applications such as real-time chat and multi-user graphical games.
For theUNIVAC 1107,UNIVAC, the first commercial computer manufacturer, produced theEXEC I operating system, andComputer Sciences Corporation developed theEXEC II operating system and delivered it to UNIVAC. EXEC II was ported to theUNIVAC 1108. Later, UNIVAC developed theEXEC 8 operating system for the 1108; it was the basis for operating systems for later members of the family. Like all early mainframe systems, EXEC I and EXEC II were a batch-oriented system that managed magnetic drums, disks, card readers and line printers; EXEC 8 supported both batch processing and on-line transaction processing. In the 1970s, UNIVAC produced the Real-Time Basic (RTB) system to support large-scale time sharing, also patterned after theDartmouth BASIC system.
Burroughs Corporation introduced theB5000 in 1961 with the MCP (Master Control Program) operating system. The B5000 was a stack machine designed to exclusively support high-level languages, with no software, not even at the lowest level of the operating system, being written directly inmachine language orassembly language; the MCP was the first[citation needed] OS to be written entirely in a high-level language -ESPOL, a dialect ofALGOL 60 - although ESPOL had specialized statements for each "syllable"[NB 2] in the B5000 instruction set. MCP also introduced many other ground-breaking innovations, such as being one of[NB 3] the first commercial implementations ofvirtual memory. The rewrite of MCP for the B6500 is now marketed as theUnisys ClearPath/MCP.
GE introduced theGE-600 series with theGeneral Electric Comprehensive Operating Supervisor (GECOS) operating system in 1962. AfterHoneywell acquired GE's computer business, it was renamed to General Comprehensive Operating System (GCOS). Honeywell expanded the use of the GCOS name to cover all its operating systems in the 1970s, though many of its computers had nothing in common with the earlier GE 600 series and their operating systems were not derived from the original GECOS.
Project MAC at MIT, working with GE andBell Labs, developedMultics, which introduced the concept of ringed security privilege levels.
Digital Equipment Corporation developedTOPS-10 for itsPDP-10 line of 36-bit computers in 1967. Before the widespread use of Unix, TOPS-10 was a particularly popular system in universities, and in the earlyARPANET community.Bolt, Beranek, and Newman developedTENEX for a modified PDP-10 that supporteddemand paging; this was another popular system in the research and ARPANET communities, and was later developed by DEC intoTOPS-20.
Scientific Data Systems/Xerox Data Systems developed several operating systems for theSigma series of computers, such as the Basic Control Monitor (BCM), Batch Processing Monitor (BPM), and Basic Time-Sharing Monitor (BTM). Later, BPM and BTM were succeeded by theUniversal Time-Sharing System (UTS); it was designed to provide multi-programming services for online (interactive) user programs in addition to batch-mode production jobs, It was succeeded by theCP-V operating system, which combined UTS with the heavily batch-orientedXerox Operating System.
Digital Equipment Corporation created several operating systems for its 16-bitPDP-11 machines, including the simpleRT-11 system, the time-sharingRSTS operating systems, and theRSX-11 family ofreal-time operating systems, as well as theVMS system for the 32-bitVAX machines.
Several competitors of Digital Equipment Corporation such asData General,Hewlett-Packard, andComputer Automation created their own operating systems. One such, "MAX III", was developed forModular Computer Systems Modcomp II and Modcomp III computers. It was characterised by its target market being the industrial control market. The Fortran libraries included one that enabled access to measurement and control devices.
IBM's key innovation in operating systems in this class (which they call "mid-range"), was their "CPF" for theSystem/38. This hadcapability-based addressing, used a machine interface architecture to isolate the application software and most of the operating system from hardware dependencies (including even such details as address size and register size) and included an integratedRDBMS. The succeeding OS/400 (now known asIBM i) for theIBM AS/400 and laterIBM Power Systems has no files, only objects of different types and these objects persist in very large, flat virtual memory, called a single-level store.
TheUnix operating system was developed at AT&T Bell Laboratories in the late 1960s, originally for thePDP-7, and later for the PDP-11. Because it was essentially free in early editions, easily obtainable, and easily modified, it achieved wide acceptance. It also became a requirement within the Bell systems operating companies. Since it was written in theC language, when that language was ported to a new machine architecture, Unix was also able to be ported. This portability permitted it to become the choice for a second generation of minicomputers and the first generation ofworkstations, and its use became widespread. Unix exemplified the idea of an operating system that was conceptually the same across various hardware platforms. Because of its utility, it inspired many and later became one of the roots of thefree software movement andopen-source software. Numerous operating systems were based upon it includingMinix,GNU/Linux, and theBerkeley Software Distribution. Apple'smacOS is also based on Unix viaNeXTSTEP[15] andFreeBSD.[16]
ThePick operating system was another operating system available on a wide variety of hardware brands. Commercially released in 1973 its core was aBASIC-like language called Data/BASIC and a SQL-style database manipulation language called ENGLISH. Licensed to a large variety of manufacturers and vendors, by the early 1980s observers saw the Pick operating system as a strong competitor to Unix.[17]
Beginning in the mid-1970s, a new class of small computers came onto the marketplace. Featuring 8-bit processors, typically theMOS Technology 6502,Intel 8080,Motorola 6800 or theZilog Z80, along with rudimentary input and output interfaces and as muchRAM as practical, these systems started out as kit-based hobbyist computers but soon evolved into an essential business tool.
While many eight-bithome computers of the 1980s, such as theBBC Micro,Commodore 64,Apple II,Atari 8-bit computers,Amstrad CPC,ZX Spectrum series and others could load a third-party disk-loading operating system, such asCP/M orGEOS, they were generally used without one. Their built-in operating systems were designed in an era whenfloppy disk drives were very expensive and not expected to be used by most users, so the standard storage device on most was atape drive using standardcompact cassettes. Most, if not all, of these computers shipped with a built-inBASIC interpreter on ROM, which also served as a crudecommand-line interface, allowing the user to load a separatedisk operating system to performfile management commands and load and save to disk. The most popular[citation needed] home computer, the Commodore 64, was a notable exception, as its DOS was on ROM in the disk drive hardware, and the drive was addressed identically to printers, modems, and other external devices.
Furthermore, those systems shipped with minimal amounts ofcomputer memory—4-8kilobytes was standard on early home computers—as well as 8-bit processors without specialized support circuitry like anMMU or even a dedicatedreal-time clock. On this hardware, a complex operating system'soverhead supporting multiple tasks and users would likely compromise the performance of the machine without really being needed. As those systems were largely sold complete, with a fixed hardware configuration, there was also no need for an operating system to provide drivers for a wide range of hardware to abstract away differences.
Video games and even the availablespreadsheet,database andword processors for home computers were mostly self-contained programs that took over the machine completely. Althoughintegrated software existed for these computers, they usually lacked features compared to their standalone equivalents, largely due to memory limitations. Data exchange was mostly performed through standard formats likeASCII text orCSV, or through specialized file conversion programs.
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Since virtually all video game consoles andarcade cabinets designed and built after 1980 were true digital machines based onmicroprocessors (unlike the earlierPong clones and derivatives), some of them carried a minimal form ofBIOS or built-in game, such as theColecoVision, theSega Master System and theSNKNeo Geo.
Modern-day game consoles and videogames, starting with thePC-Engine, all have a minimal BIOS that also provides some interactive utilities such asmemory card management,audio orvideo CD playback,copy protection and sometimes carrylibraries for developers to use etc. Few of these cases, however, would qualify as a true operating system.
The most notable exceptions are probably theDreamcast game console which includes a minimal BIOS, like thePlayStation, but can load theWindows CE operating system from the game disk allowing easily porting of games from thePC world, and theXbox game console, which is little more than a disguised Intel-basedPC running a secret, modified version ofMicrosoft Windows in the background. Furthermore, there areLinux versions that will run on aDreamcast and later game consoles as well.
Long before that,Sony had released a kind ofdevelopment kit called theNet Yaroze for its first PlayStation platform, which provided a series of programming and developing tools to be used with a normal PC and a specially modified "Black PlayStation" that could be interfaced with a PC and download programs from it. These operations require in general a functional OS on both platforms involved.
In general, it can be said that videogame consoles and arcade coin-operated machines used at most a built-inBIOS during the 1970s, 1980s and most of the 1990s, while from the PlayStation era and beyond they started getting more and more sophisticated, to the point of requiring a generic or custom-built OS for aiding in development and expandability.
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The development of microprocessors made inexpensive computing available for thesmall business and hobbyist, which in turn led to the widespread use of interchangeable hardware components using a common interconnection (such as theS-100, SS-50,Apple II,ISA, andPCIbuses), and an increasing need for "standard" operating systems to control them. The most important of the early OSes on these machines wasDigital Research'sCP/M-80 for the 8080 / 8085 / Z80 CPUs. It was based on several Digital Equipment Corporation operating systems, mostly for the PDP-11 architecture. Microsoft's first operating system,MDOS/MIDAS, was designed along many of the PDP-11 features, but for microprocessor based systems.MS-DOS, orPC DOS when supplied by IBM, was designed to be similar to CP/M-80.[18] Each of these machines had a small boot program in ROM which loaded the OS itself from disk. The BIOS on the IBM-PC class machines was an extension of this idea and has accreted more features and functions in the 20 years since the first IBM-PC was introduced in 1981.
The decreasing cost of display equipment and processors made it practical to provide graphical user interfaces for many operating systems, such as the genericX Window System that is provided with many Unix systems, or other graphical systems such asApple'sclassic Mac OS andmacOS, theRadio Shack Color Computer'sOS-9 Level II/Multi-Vue,Commodore'sAmigaOS,Atari TOS,IBM'sOS/2, andMicrosoft Windows. The original GUI was developed on theXerox Alto computer system at XeroxPalo Alto Research Center in the early 1970s and commercialized by many vendors throughout the 1980s and 1990s.
Since the late 1990s, there have been three operating systems in widespread use on personal computers:Apple Inc.'smacOS, theopen sourceLinux, andMicrosoft Windows. Since 2005 and theMac transition to Intel processors, all have been developed mainly on thex86 platform, although macOS retainedPowerPC support until 2009 and Linux remains ported to a multitude of architectures including ones such as68k,PA-RISC, andDEC Alpha, which have been long superseded and out of production, andSPARC andMIPS, which are used in servers or embedded systems but no longer for desktop computers. Other operating systems such as AmigaOS and OS/2 remain in use, if at all, mainly byretrocomputing enthusiasts or for specialized embedded applications.
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In the early 1990s,Psion released thePsion Series 3PDA, a small mobile computing device. It supported user-written applications running on an operating system calledEPOC. Later versions of EPOC becameSymbian, an operating system used for mobile phones fromNokia,Ericsson,Sony Ericsson,Motorola,Samsung and phones developed forNTT Docomo bySharp,Fujitsu &Mitsubishi.Symbian was the world's most widely used smartphone operating system until 2010 with a peak market share of 74% in 2006. In 1996,Palm Computing released thePilot 1000 and Pilot 5000, runningPalm OS. MicrosoftWindows CE was the base for Pocket PC 2000, renamedWindows Mobile in 2003, which at its peak in 2007 was the most common operating system for smartphones in the U.S.
In 2007, Apple introduced theiPhone and its operating system, known as simplyiPhone OS (until the release ofiOS 4), which, likeMac OS X, is based on theUnix-likeDarwin. In addition to these underpinnings, it also introduced a powerful and innovative graphic user interface that was later also used on thetablet computeriPad. A year later,Android, with its own graphical user interface, was introduced, based on a modifiedLinux kernel, andMicrosoft re-entered the mobile operating system market withWindows Phone in 2010, which was replaced byWindows 10 Mobile in 2015.
In addition to these, a wide range of othermobile operating systems are contending in this area.
Operating systems originally ran directly on the hardware itself and provided services to applications, but with virtualization, the operating system itself runs under the control of ahypervisor, instead of being in direct control of the hardware.
On mainframes IBM introduced the notion of avirtual machine in 1968 withCP/CMS on theIBM System/360 Model 67, and extended this later in 1972 withVirtual Machine Facility/370 (VM/370) onSystem/370.
Onx86-basedpersonal computers,VMware popularized this technology with their 1999 product,VMware Workstation,[19] and their 2001 VMware GSX Server and VMware ESX Server products.[20] Later, a wide range of products from others, includingXen,KVM andHyper-V meant that by 2010 it was reported that more than 80 percent of enterprises had a virtualization program or project in place, and that 25 percent of all server workloads would be in a virtual machine.[21]
Over time, the line between virtual machines, monitors, and operating systems was blurred:
In many ways, virtual machine software today plays the role formerly held by the operating system, including managing the hardware resources (processor, memory, I/O devices), applying scheduling policies, or allowing system administrators to manage the system.
