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129-507: The Dartmouth Time-Sharing System ( DTSS ) is a discontinued operating system first developed at Dartmouth College between 1963 and 1964. It was the first successful large-scale time-sharing system to be implemented, and was also the system for which the BASIC language was developed. DTSS was developed continually over the next decade, reimplemented on several generations of computers, and finally shut down in 1999. General Electric developed

258-668: A Royal McBee LGP-30 computer around 1959, which was programmed by undergraduates in assembly language. Kurtz and four students programmed the Dartmouth ALGOL 30 compiler , an implementation of the ALGOL 58 programming language, which two of the students, Stephen Garland and Anthony Knapp then evolved into the SCALP (Self Contained ALgol Processor) language between 1962 and 1964. Kemeny and freshman Sidney Marshall collaborated to create DOPE (Dartmouth Oversimplified Programming Experiment) , which

387-428: A system call to perform a block I/O write operation, then the system call might execute the following instructions: While the writing takes place, the operating system will context switch to other processes as normal. When the device finishes writing, the device will interrupt the currently running process by asserting an interrupt request . The device will also place an integer onto the data bus. Upon accepting

516-479: A 1969 conference: Communication files supported read, write and close operations, but also synchronous and asynchronous data transfer, random access, status inquiries, out-of-band signaling, error reporting, and access control, with the precise semantics of each operation determined by the master process. As Douglas McIlroy notes: "In this, [communication files were] more akin to Plan 9 's 9P protocol than to familiar IO." A notable application of communication files

645-645: A computer even if they are not compatible with the base operating system. A library operating system (libOS) is one in which the services that a typical operating system provides, such as networking, are provided in the form of libraries and composed with a single application and configuration code to construct a unikernel : a specialized (only the absolute necessary pieces of code are extracted from libraries and bound together ), single address space , machine image that can be deployed to cloud or embedded environments. The operating system code and application code are not executed in separated protection domains (there

774-571: A considerable extent. Some devices with a poorly designed programming interface provide no way to determine whether they have requested service. They may lock up or otherwise misbehave if serviced when they do not want it. Such devices cannot tolerate spurious interrupts, and so also cannot tolerate sharing an interrupt line. ISA cards, due to often cheap design and construction, are notorious for this problem. Such devices are becoming much rarer, as hardware logic becomes cheaper and new system architectures mandate shareable interrupts. Some systems use

903-571: A development of MULTICS for a single user. Because UNIX's source code was available, it became the basis of other, incompatible operating systems, of which the most successful were AT&T 's System V and the University of California 's Berkeley Software Distribution (BSD). To increase compatibility, the IEEE released the POSIX standard for operating system application programming interfaces (APIs), which

1032-453: A device, the processor may again poll and, if necessary, service other devices before exiting the ISR. An edge-triggered interrupt is an interrupt signaled by a level transition on the interrupt line, either a falling edge (high to low) or a rising edge (low to high). A device wishing to signal an interrupt drives a pulse onto the line and then releases the line to its inactive state. If the pulse

1161-589: A document about their proposed system design, which they presented to GE's Phoenix office in 1962. However, GE rejected the partnership, and its October 1962 proposal to Dartmouth was framed solely as a commercial sale. That said, GE and Dartmouth promoted the operational Dartmouth Time Sharing System in October 1964 at the Fall Joint Computer Conference in San Francisco, with three teletypes connected to

1290-414: A fear of the machine. After a brief period at the console, when the student might play a football game or write a few simple programs, he comes away with a much different relationship. The fear and mystery of the computer are suddenly gone. As of 1971 57% of DTSS use was for courses and 16% for research. Kemeny and Kurtz intended for students in technical and nontechnical fields to use DTSS. They arranged for

1419-410: A further interrupt. This contrasts with a level trigger where the low level would continue to create interrupts (if they are enabled) until the signal returns to its high level. Computers with edge-triggered interrupts may include an interrupt register that retains the status of pending interrupts. Systems with interrupt registers generally have interrupt mask registers as well. The processor samples

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1548-452: A hybrid of level-triggered and edge-triggered signaling. The hardware not only looks for an edge, but it also verifies that the interrupt signal stays active for a certain period of time. A common use of a hybrid interrupt is for the NMI (non-maskable interrupt) input. Because NMIs generally signal major – or even catastrophic – system events, a good implementation of this signal tries to ensure that

1677-484: A large legal settlement was paid. In the twenty-first century, Windows continues to be popular on personal computers but has less market share of servers. UNIX operating systems, especially Linux, are the most popular on enterprise systems and servers but are also used on mobile devices and many other computer systems. On mobile devices, Symbian OS was dominant at first, being usurped by BlackBerry OS (introduced 2002) and iOS for iPhones (from 2007). Later on,

1806-442: A library with no protection between applications, such as eCos . A hypervisor is an operating system that runs a virtual machine . The virtual machine is unaware that it is an application and operates as if it had its own hardware. Virtual machines can be paused, saved, and resumed, making them useful for operating systems research, development, and debugging. They also enhance portability by enabling applications to be run on

1935-447: A malformed machine instruction . However, the most common error conditions are division by zero and accessing an invalid memory address . Users can send messages to the kernel to modify the behavior of a currently running process. For example, in the command-line environment , pressing the interrupt character (usually Control-C ) might terminate the currently running process. To generate software interrupts for x86 CPUs,

2064-413: A particular (rising or falling) edge will cause a service request to be latched; the processor resets the latch when the interrupt handler executes. A level-triggered interrupt is requested by holding the interrupt signal at its particular (high or low) active logic level . A device invokes a level-triggered interrupt by driving the signal to and holding it at the active level. It negates the signal when

2193-455: A particular application's memory is stored, or even whether or not it has been allocated yet. In modern operating systems, memory which is accessed less frequently can be temporarily stored on a disk or other media to make that space available for use by other programs. This is called swapping , as an area of memory can be used by multiple programs, and what that memory area contains can be swapped or exchanged on demand. Virtual memory provides

2322-960: A period - and unless there is some type of hardware latch that records the event it is impossible to recover. This problem caused many "lockups" in early computer hardware because the processor did not know it was expected to do something. More modern hardware often has one or more interrupt status registers that latch interrupts requests; well-written edge-driven interrupt handling code can check these registers to ensure no events are missed. The Industry Standard Architecture (ISA) bus uses edge-triggered interrupts, without mandating that devices be able to share IRQ lines, but all mainstream ISA motherboards include pull-up resistors on their IRQ lines, so well-behaved ISA devices sharing IRQ lines should just work fine. The parallel port also uses edge-triggered interrupts. Many older devices assume that they have exclusive use of IRQ lines, making it electrically unsafe to share them. There are three ways multiple devices "sharing

2451-503: A precursor to the Unix talk program. While several languages were available on DTSS, as of 1972 98% of programs were written in Dartmouth BASIC. Because BASIC did not change, the system remained compatible with older applications; Kemeny reported in 1974 that programs he had written in 1964 would still run. By 1980, supported languages and systems included: In 2000, a project to recreate

2580-503: A program does not interfere with memory already in use by another program. Since programs time share, each program must have independent access to memory. Cooperative memory management, used by many early operating systems, assumes that all programs make voluntary use of the kernel 's memory manager, and do not exceed their allocated memory. This system of memory management is almost never seen any more, since programs often contain bugs which can cause them to exceed their allocated memory. If

2709-408: A program fails, it may cause memory used by one or more other programs to be affected or overwritten. Malicious programs or viruses may purposefully alter another program's memory, or may affect the operation of the operating system itself. With cooperative memory management, it takes only one misbehaved program to crash the system. Memory protection enables the kernel to limit a process' access to

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2838-440: A program tries to access memory that is not accessible memory, but nonetheless has been allocated to it, the kernel is interrupted (see § Memory management ) . This kind of interrupt is typically a page fault . When the kernel detects a page fault it generally adjusts the virtual memory range of the program which triggered it, granting it access to the memory requested. This gives the kernel discretionary power over where

2967-501: A restart of the program. Arm uses the term exception to refer to all types of interrupts, and divides exceptions into (hardware) interrupts , aborts , reset , and exception-generating instructions. Aborts correspond to x86 exceptions and may be prefetch aborts (failed instruction fetches) or data aborts (failed data accesses), and may be synchronous or asynchronous. Asynchronous aborts may be precise or imprecise. MMU aborts (page faults) are synchronous. RISC-V uses interrupt as

3096-508: A serious research problem, doing his homework the easy way, playing a game of football, or writing a letter to his girlfriend". By 1972 the football simulation supported simultaneous head-to-head play as a multiplayer video game . Kiewit's location near Dartmouth College Greek organizations made it popular for socializing; students often brought dates to the Computation Center, both to play games and to demonstrate their own programs. By

3225-467: A significant amount of CPU time. Direct memory access (DMA) is an architecture feature to allow devices to bypass the CPU and access main memory directly. (Separate from the architecture, a device may perform direct memory access to and from main memory either directly or via a bus.) When a computer user types a key on the keyboard, typically the character appears immediately on the screen. Likewise, when

3354-453: A similar system based on an interim version of DTSS, which they referred to as Mark II. Mark II and the further developed Mark III were widely used on their GE-600 series mainframe computers and formed the basis for their online services . These were the largest such services in the world for a time, eventually emerging as the consumer-oriented GEnie online service. Professors John Kemeny and Thomas Kurtz at Dartmouth College purchased

3483-402: A specific moment in time. Hard real-time systems require exact timing and are common in manufacturing , avionics , military, and other similar uses. With soft real-time systems, the occasional missed event is acceptable; this category often includes audio or multimedia systems, as well as smartphones. In order for hard real-time systems be sufficiently exact in their timing, often they are just

3612-429: A synchronous interrupt caused by an exceptional condition (e.g., division by zero , invalid memory access , illegal opcode ), although the term exception is more common for this. x86 divides interrupts into (hardware) interrupts and software exceptions , and identifies three types of exceptions: faults, traps, and aborts. (Hardware) interrupts are interrupts triggered asynchronously by an I/O device, and allow

3741-418: A system misbehaves. In a wired-OR circuit, parasitic capacitance charging/discharging through the interrupt line's bias resistor will cause a small delay before the processor recognizes that the interrupt source has been cleared. If the interrupting device is cleared too late in the interrupt service routine (ISR), there will not be enough time for the interrupt circuit to return to the quiescent state before

3870-471: A trigger table (a table of functions) in its header, which both the app and OS know of and use appropriately that is not related to hardware. However do not confuse this with hardware interrupts which signal the CPU (the CPU enacts software from a table of functions, similarly to software interrupts). Multiple devices sharing an interrupt line (of any triggering style) all act as spurious interrupt sources with respect to each other. With many devices on one line,

3999-577: A type reserved for interrupts, or it might be of some pre-existing type such as a memory write. Message-signalled interrupts behave very much like edge-triggered interrupts, in that the interrupt is a momentary signal rather than a continuous condition. Interrupt-handling software treats the two in much the same manner. Typically, multiple pending message-signaled interrupts with the same message (the same virtual interrupt line) are allowed to merge, just as closely spaced edge-triggered interrupts can merge. Message-signalled interrupt vectors can be shared, to

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4128-417: A user moves a mouse , the cursor immediately moves across the screen. Each keystroke and mouse movement generates an interrupt called Interrupt-driven I/O . An interrupt-driven I/O occurs when a process causes an interrupt for every character or word transmitted. Devices such as hard disk drives , solid-state drives , and magnetic tape drives can transfer data at a rate high enough that interrupting

4257-453: A variation of the classic reader/writer problem . The writer receives a pipe from the shell for its output to be sent to the reader's input stream. The command-line syntax is alpha | bravo . alpha will write to the pipe when its computation is ready and then sleep in the wait queue. bravo will then be moved to the ready queue and soon will read from its input stream. The kernel will generate software interrupts to coordinate

4386-404: A variety of purposes, such as requesting operating system services and interacting with device drivers (e.g., to read or write storage media). Software interrupts may also be triggered by program execution errors or by the virtual memory system. Typically, the operating system kernel will catch and handle such interrupts. Some interrupts are handled transparently to the program - for example,

4515-418: Is interrupted by it. Operating systems are found on many devices that contain a computer – from cellular phones and video game consoles to web servers and supercomputers . In the personal computer market, as of September 2024 , Microsoft Windows holds a dominant market share of around 73%. macOS by Apple Inc. is in second place (15%), Linux is in third place (5%), and ChromeOS

4644-562: Is remote direct memory access , which enables each CPU to access memory belonging to other CPUs. Multicomputer operating systems often support remote procedure calls where a CPU can call a procedure on another CPU, or distributed shared memory , in which the operating system uses virtualization to generate shared memory that does not physically exist. A distributed system is a group of distinct, networked computers—each of which might have their own operating system and file system. Unlike multicomputers, they may be dispersed anywhere in

4773-484: Is a change away from the currently running process. Similarly, both hardware and software interrupts execute an interrupt service routine . Software interrupts may be normally occurring events. It is expected that a time slice will occur, so the kernel will have to perform a context switch . A computer program may set a timer to go off after a few seconds in case too much data causes an algorithm to take too long. Software interrupts may be error conditions, such as

4902-411: Is deferred or ignored by the processor, while to unmask an interrupt is to enable it. Processors typically have an internal interrupt mask register, which allows selective enabling (and disabling) of hardware interrupts. Each interrupt signal is associated with a bit in the mask register. On some systems, the interrupt is enabled when the bit is set, and disabled when the bit is clear. On others,

5031-422: Is difficult to define, but has been called "the layer of software that manages a computer's resources for its users and their applications ". Operating systems include the software that is always running, called a kernel —but can include other software as well. The two other types of programs that can run on a computer are system programs —which are associated with the operating system, but may not be part of

5160-896: Is in fourth place (2%). In the mobile sector (including smartphones and tablets ), as of September 2023 , Android's share is 68.92%, followed by Apple's iOS and iPadOS with 30.42%, and other operating systems with .66%. Linux distributions are dominant in the server and supercomputing sectors. Other specialized classes of operating systems (special-purpose operating systems), such as embedded and real-time systems, exist for many applications. Security-focused operating systems also exist. Some operating systems have low system requirements (e.g. light-weight Linux distribution ). Others may have higher system requirements. Some operating systems require installation or may come pre-installed with purchased computers ( OEM -installation), whereas others may run directly from media (i.e. live CD ) or flash memory (i.e. USB stick). An operating system

5289-421: Is no OS, from the bare metal program running on the CPU. Such external devices may be part of the computer (e.g., disk controller ) or they may be external peripherals . For example, pressing a keyboard key or moving a mouse plugged into a PS/2 port triggers hardware interrupts that cause the processor to read the keystroke or mouse position. Hardware interrupts can arrive asynchronously with respect to

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5418-416: Is no clear consensus as to the exact meaning of these terms". The term trap may refer to any interrupt, to any software interrupt, to any synchronous software interrupt, or only to interrupts caused by instructions with trap in their names. In some usages, the term trap refers specifically to a breakpoint intended to initiate a context switch to a monitor program or debugger . It may also refer to

5547-443: Is only a single application running, at least conceptually, so there is no need to prevent interference between applications) and OS services are accessed via simple library calls (potentially inlining them based on compiler thresholds), without the usual overhead of context switches , in a way similarly to embedded and real-time OSes. Note that this overhead is not negligible: to the direct cost of mode switching it's necessary to add

5676-413: Is requested by the processor itself upon executing particular instructions or when certain conditions are met. Every software interrupt signal is associated with a particular interrupt handler. A software interrupt may be intentionally caused by executing a special instruction which, by design, invokes an interrupt when executed. Such instructions function similarly to subroutine calls and are used for

5805-499: Is supported by most UNIX systems. MINIX was a stripped-down version of UNIX, developed in 1987 for educational uses, that inspired the commercially available, free software Linux . Since 2008, MINIX is used in controllers of most Intel microchips , while Linux is widespread in data centers and Android smartphones. The invention of large scale integration enabled the production of personal computers (initially called microcomputers ) from around 1980. For around five years,

5934-473: Is that they do not load user-installed software. Consequently, they do not need protection between different applications, enabling simpler designs. Very small operating systems might run in less than 10 kilobytes , and the smallest are for smart cards . Examples include Embedded Linux , QNX , VxWorks , and the extra-small systems RIOT and TinyOS . A real-time operating system is an operating system that guarantees to process events or data by or at

6063-427: Is the default state of it. Devices signal an interrupt by briefly driving the line to its non-default state, and let the line float (do not actively drive it) when not signaling an interrupt. This type of connection is also referred to as open collector . The line then carries all the pulses generated by all the devices. (This is analogous to the pull cord on some buses and trolleys that any passenger can pull to signal

6192-435: Is the part of the operating system that provides protection between different applications and users. This protection is key to improving reliability by keeping errors isolated to one program, as well as security by limiting the power of malicious software and protecting private data, and ensuring that one program cannot monopolize the computer's resources. Most operating systems have two modes of operation: in user mode ,

6321-440: Is too short to be detected by polled I/O then special hardware may be required to detect it. The important part of edge triggering is that the signal must transition to trigger the interrupt; for example, if the signal was high-low-low, there would only be one falling edge interrupt triggered, and the continued low level would not trigger a further interrupt. The signal must return to the high level and fall again in order to trigger

6450-535: The CP/M (Control Program for Microcomputers) was the most popular operating system for microcomputers. Later, IBM bought the DOS (Disk Operating System) from Microsoft . After modifications requested by IBM, the resulting system was called MS-DOS (MicroSoft Disk Operating System) and was widely used on IBM microcomputers. Later versions increased their sophistication, in part by borrowing features from UNIX. Apple 's Macintosh

6579-496: The INT assembly language instruction is available. The syntax is INT X , where X is the offset number (in hexadecimal format) to the interrupt vector table . To generate software interrupts in Unix-like operating systems, the kill(pid,signum) system call will send a signal to another process. pid is the process identifier of the receiving process. signum is

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6708-598: The University of Vermont , and Vermont Technical College . By 1971, the Kiewit Network connected 30 high schools and 20 colleges in New England, New York, and New Jersey. At that time, DTSS was supporting over 30,000 users, of which only 3,000 were at Dartmouth College. By 1973, the Kiewit Network had expanded to include schools in Illinois, Michigan, upstate New York, Ohio, and Montreal, Canada . No student at Dartmouth has

6837-457: The registrar and housing office among users. 27% of DTSS use as of 1971 was for casual use and entertainment, which the university stated "is in no sense regarded as frivolous", as such was an enjoyable way for users to become familiar with and not fear the computer. The library of hundreds of programs included, Kemeny and Kurtz reported, " many games ". They were pleased by the widespread faculty use of DTSS, and that many students continued using

6966-420: The transistor in the mid-1950s, mainframes began to be built. These still needed professional operators who manually do what a modern operating system would do, such as scheduling programs to run, but mainframes still had rudimentary operating systems such as Fortran Monitor System (FMS) and IBSYS . In the 1960s, IBM introduced the first series of intercompatible computers ( System/360 ). All of them ran

7095-457: The 1964 CDC 3600 , all interrupts went to the same location, and the OS used a specialized instruction to determine the highest-priority outstanding unmasked interrupt. On contemporary systems, there is generally a distinct interrupt routine for each type of interrupt (or for each interrupt source), often implemented as one or more interrupt vector tables . To mask an interrupt is to disable it, so it

7224-430: The 1967–68 school year, in addition to 2,600 Dartmouth users, 5,550 people at ten universities and 23 high schools accessed DTSS. Kemeny had a terminal at home, and as president installed one in his office. By the early 1970s the campus had more than 150 terminals in 25 buildings, including portable units for patients at the campus infirmary. About 2,000 users logged into DTSS each day; 80% of students and 70% of faculty used

7353-542: The 1970s, later versions moved to Honeywell 6000 series mainframes (1973) and Honeywell 716 communication processors (1974). In 1976 the GE-635 system was replaced by a Honeywell 66/40A computer. It remained in operation until the end of 1999. DTSS, version 2, included a novel form of inter-process communication called "communication files". They significantly antedated Unix pipes , as design documents put their conceptual origin sometime in 1967, and were described briefly in

7482-406: The CPU and another component such as a programmable interrupt controller or a southbridge . If an additional component is used, that component would be connected between the interrupting device and the processor's interrupt pin to multiplex several sources of interrupt onto the one or two CPU lines typically available. If implemented as part of the memory controller , interrupts are mapped into

7611-410: The CPU for every byte or word transferred, and having the CPU transfer the byte or word between the device and memory, would require too much CPU time. Data is, instead, transferred between the device and memory independently of the CPU by hardware such as a channel or a direct memory access controller; an interrupt is delivered only when all the data is transferred. If a computer program executes

7740-474: The CPU to re-enter supervisor mode , placing the kernel in charge. This is called a segmentation violation or Seg-V for short, and since it is both difficult to assign a meaningful result to such an operation, and because it is usually a sign of a misbehaving program, the kernel generally resorts to terminating the offending program, and reports the error. Windows versions 3.1 through ME had some level of memory protection, but programs could easily circumvent

7869-554: The DATANET-30 provided the user-interface and scheduler, while user programs ran in the GE-225. Its implementation began in 1963, by a student team under the direction of Kemeny and Kurtz with the aim of providing easy access to computing facilities for all members of the college. The GE-225 and DATANET-30 computers arrived in February 1964. Two students, John McGeachie and Michael Busch, wrote

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7998-526: The DTSS system on a simulator was undertaken and as a result DTSS is now available for Microsoft Windows systems and for the Apple Macintosh computer. Operating system An operating system ( OS ) is system software that manages computer hardware and software resources, and provides common services for computer programs . Time-sharing operating systems schedule tasks for efficient use of

8127-618: The Dartmouth system in Hanover. From December 1964 into January 1965, two Dartmouth students installed working copies of DTSS and BASIC on GE computers in Phoenix. In early 1965, GE began to advertise timesharing services on its GE-265 system (GE 235 + DATANET 30), including BASIC and Dartmouth Algol, later renaming it the GE Mark I time-sharing system. Over the next few years, GE opened 25 computer centers in

8256-531: The GE Mark II system. In parallel with this work, Dartmouth embarked in 1967 on the development of Phase II under the direction of Professor John Kemeny, with programming carried out by students and faculty. Phase II of the Dartmouth Time-Sharing System replaced Phase I on April 1, 1969, at Dartmouth. As described in 1969, the new DTSS architecture was influenced by three criteria: This new version

8385-447: The ISR does not account for the possibility of such an interrupt occurring. As spurious interrupts are mostly a problem with wired-OR interrupt circuits, good programming practice in such systems is for the ISR to check all interrupt sources for activity and take no action (other than possibly logging the event) if none of the sources is interrupting. They may even lead to crashing of the computer in adverse scenarios. A software interrupt

8514-540: The Kiewit Computation Center that housed the DTSS computers and staff. These schools connected to DTSS via one or more teletypes, modems, and dial-up telephone lines. Dartmouth students had free, unlimited access to DTSS, but high-school students had quotas of 40 to 72 hours of terminal access each week, and college users paid for computer use. Dartmouth ran active programs to engage and train high school teachers in using computation within their courses. By 1967,

8643-627: The United States and elsewhere, serving over fifty thousand users. The Computer History Museum 's Corporate Histories Collection describes GE's Mark I history this way: From 1966 to 1968, DTSS was reimplemented on the GE 635 , still using the DATANET-30 for terminal control. The GE 635 system was delivered in November 1966. By October 1967, it was providing a service based on Phase I software, jointly developed by Dartmouth and GE, which GE subsequently marketed as

8772-492: The VARY ONLINE command will simulate a device end interrupt on the target device. A spurious interrupt is a hardware interrupt for which no source can be found. The term "phantom interrupt" or "ghost interrupt" may also be used to describe this phenomenon. Spurious interrupts tend to be a problem with a wired-OR interrupt circuit attached to a level-sensitive processor input. Such interrupts may be difficult to identify when

8901-534: The application program, which then interacts with the user and with hardware devices. However, in some systems an application can request that the operating system execute another application within the same process, either as a subroutine or in a separate thread, e.g., the LINK and ATTACH facilities of OS/360 and successors . An interrupt (also known as an abort , exception , fault , signal , or trap ) provides an efficient way for most operating systems to react to

9030-456: The callback is made using Structured Exception Handling with an exception code such as STATUS_ACCESS_VIOLATION or STATUS_INTEGER_DIVIDE_BY_ZERO. In a kernel process , it is often the case that some types of software interrupts are not supposed to happen. If they occur nonetheless, an operating system crash may result. The terms interrupt , trap , exception , fault , and abort are used to distinguish types of interrupts, although "there

9159-401: The card equipment, the tape drives, and the high-speed printer during time-sharing through interrupt processing. Two algebraic languages, BASIC and ALGOL, are available, with FORTRAN planned for September 1965. These one-pass compilers are rather fast, requiring usually 1 to 4 seconds per compilation. Kemeny and Kurtz observed that "any response time which averages more than 10 seconds destroys

9288-453: The computer's memory. Various methods of memory protection exist, including memory segmentation and paging . All methods require some level of hardware support (such as the 80286 MMU), which does not exist in all computers. In both segmentation and paging, certain protected mode registers specify to the CPU what memory address it should allow a running program to access. Attempts to access other addresses trigger an interrupt, which causes

9417-608: The current instance of the ISR terminates. The result is the processor will think another interrupt is pending, since the voltage at its interrupt request input will be not high or low enough to establish an unambiguous internal logic 1 or logic 0. The apparent interrupt will have no identifiable source, hence the "spurious" moniker. A spurious interrupt may also be the result of electrical anomalies due to faulty circuit design, high noise levels, crosstalk , timing issues, or more rarely, device errata . A spurious interrupt may result in system deadlock or other undefined operation if

9546-471: The details of how interrupt service routines behave vary from operating system to operating system. However, several interrupt functions are common. The architecture and operating system must: A software interrupt is a message to a process that an event has occurred. This contrasts with a hardware interrupt — which is a message to the central processing unit (CPU) that an event has occurred. Software interrupts are similar to hardware interrupts — there

9675-410: The driver that they are requesting a stop.) However, interrupt pulses from different devices may merge if they occur close in time. To avoid losing interrupts the CPU must trigger on the trailing edge of the pulse (e.g. the rising edge if the line is pulled up and driven low). After detecting an interrupt the CPU must check all the devices for service requirements. Edge-triggered interrupts do not suffer

9804-422: The environment. Interrupts cause the central processing unit (CPU) to have a control flow change away from the currently running program to an interrupt handler , also known as an interrupt service routine (ISR). An interrupt service routine may cause the central processing unit (CPU) to have a context switch . The details of how a computer processes an interrupt vary from architecture to architecture, and

9933-451: The failure might affect only a single process or might have global impact. Some operating systems have code specifically to deal with this. As an example, IBM Operating System/360 (OS/360) relies on a not-ready to ready device-end interrupt when a tape has been mounted on a tape drive, and will not read the tape label until that interrupt occurs or is simulated. IBM added code in OS/360 so that

10062-615: The first occurrence of interrupt masking. The National Bureau of Standards DYSEAC (1954) was the first to use interrupts for I/O. The IBM 704 was the first to use interrupts for debugging , with a "transfer trap", which could invoke a special routine when a branch instruction was encountered. The MIT Lincoln Laboratory TX-2 system (1957) was the first to provide multiple levels of priority interrupts. Interrupt signals may be issued in response to hardware or software events. These are classified as hardware interrupts or software interrupts , respectively. For any particular processor,

10191-690: The following New England high schools: Cape Elizabeth High School , Concord High School , Hartford High School (Vermont), Keene High School , Lebanon High School , Loomis School , Manchester Central High School , Rutland High School , St. Johnsbury Academy , South Portland High School , and Timberlane High School . From 1968 to 1970, Dartmouth added a number of colleges to the Kiewit Network via its Regional College Consortium. They included: Bates College, Berkshire Community College , Bowdoin College , Colby Junior College , Middlebury College , Mount Holyoke College , New England College , Norwich University ,

10320-601: The following high schools had joined the Kiewit Network: Hanover High School, The Holderness School , Mascoma Valley Regional High School , Kimball Union Academy , Mount Hermon School , Phillips Andover Academy , Phillips Exeter Academy , St. Paul's School , and Vermont Academy . This group expanded in the Dartmouth Secondary School Project, funded by the NSF during 1967–1968, which added

10449-410: The hardware checks that the software is only executing legal instructions, whereas the kernel has unrestricted powers and is not subject to these checks. The kernel also manages memory for other processes and controls access to input/output devices. The operating system provides an interface between an application program and the computer hardware, so that an application program can interact with

10578-493: The hardware only by obeying rules and procedures programmed into the operating system. The operating system is also a set of services which simplify development and execution of application programs. Executing an application program typically involves the creation of a process by the operating system kernel , which assigns memory space and other resources, establishes a priority for the process in multi-tasking systems, loads program binary code into memory, and initiates execution of

10707-488: The heaviest users surprised Kemeny. By 1972 90% of students had computer experience; because faculty knew that students were familiar with DTSS, using it became a routine part of many courses. A 1975 survey found that 29% of faculty used the computer in courses and 73% of students were enrolled in them, 43% of faculty used it in research, and 45% of faculty had written a computer program. By that year university administration used 28% of timesharing resources to students' 20%, with

10836-401: The highest priority enabled interrupt. In others, there are separate interrupt handlers for separate interrupt types, separate I/O channels or devices, or both. Several interrupt causes may have the same interrupt type and thus the same interrupt handler, requiring the interrupt handler to determine the cause. Interrupts may be fully handled in hardware by the CPU, or may be handled by both

10965-453: The illusion of having one's own computer", so DTSS's design emphasized immediate feedback. Many of its users thus believed that their terminal was the computer and that, Kemeny wrote, "the machine is there just to serve him and that he has complete control of the entire system". Because of the educational aims, ease of use was a priority in DTSS design. It implemented the world's first Integrated Design Environment (IDE). Any line typed in by

11094-418: The indirect pollution of important processor structures (like CPU caches , the instruction pipeline , and so on) which affects both user-mode and kernel-mode performance. The first computers in the late 1940s and 1950s were directly programmed either with plugboards or with machine code inputted on media such as punch cards , without programming languages or operating systems. After the introduction of

11223-400: The interrupt is valid by verifying that it remains active for a period of time. This 2-step approach helps to eliminate false interrupts from affecting the system. A message-signaled interrupt does not use a physical interrupt line. Instead, a device signals its request for service by sending a short message over some communications medium, typically a computer bus . The message might be of

11352-404: The interrupt request, the operating system will: When the writing process has its time slice expired, the operating system will: With the program counter now reset, the interrupted process will resume its time slice. Among other things, a multiprogramming operating system kernel must be responsible for managing all system memory which is currently in use by the programs. This ensures that

11481-440: The interrupt trigger signals or interrupt register during each instruction cycle, and will process the highest priority enabled interrupt found. Regardless of the triggering method, the processor will begin interrupt processing at the next instruction boundary following a detected trigger, thus ensuring: There are several different architectures for handling interrupts. In some, there is a single interrupt handler that must scan for

11610-431: The kernel—and applications—all other software. There are three main purposes that an operating system fulfills: With multiprocessors multiple CPUs share memory. A multicomputer or cluster computer has multiple CPUs, each of which has its own memory . Multicomputers were developed because large multiprocessors are difficult to engineer and prohibitively expensive; they are universal in cloud computing because of

11739-400: The memory allocated to a different one. Around the same time, teleprinters began to be used as terminals so multiple users could access the computer simultaneously. The operating system MULTICS was intended to allow hundreds of users to access a large computer. Despite its limited adoption, it can be considered the precursor to cloud computing . The UNIX operating system originated as

11868-408: The need to use it. A general protection fault would be produced, indicating a segmentation violation had occurred; however, the system would often crash anyway. The use of virtual memory addressing (such as paging or segmentation) means that the kernel can choose what memory each program may use at any given time, allowing the operating system to use the same memory locations for multiple tasks. If

11997-423: The normal resolution of a page fault is to make the required page accessible in physical memory. But in other cases such as a segmentation fault the operating system executes a process callback. On Unix-like operating systems this involves sending a signal such as SIGSEGV , SIGBUS , SIGILL or SIGFPE , which may either call a signal handler or execute a default action (terminating the program). On Windows

12126-481: The number of interrupt types is limited by the architecture. A hardware interrupt is a condition related to the state of the hardware that may be signaled by an external hardware device, e.g., an interrupt request (IRQ) line on a PC, or detected by devices embedded in processor logic (e.g., the CPU timer in IBM System/370), to communicate that the device needs attention from the operating system (OS) or, if there

12255-408: The open-source Android operating system (introduced 2008), with a Linux kernel and a C library ( Bionic ) partially based on BSD code, became most popular. The components of an operating system are designed to ensure that various parts of a computer function cohesively. With the de facto obsoletion of DOS , all user software must interact with the operating system to access hardware. The kernel

12384-403: The operating systems for the DATANET-30 and GE-225; Kemeny contributed the BASIC compiler. The system became operational in mid March, and on May 1, 1964, at 4:00 a.m., the system began operations. In autumn of 1964, hundreds of freshman students began to use the system via 20 teletypes , with access at Hanover High School via one additional teletype; later that autumn the GE-225 computer

12513-414: The overall term as well as for the external subset; internal interrupts are called exceptions. Each interrupt signal input is designed to be triggered by either a logic signal level or a particular signal edge (level transition). Level-sensitive inputs continuously request processor service so long as a particular (high or low) logic level is applied to the input. Edge-sensitive inputs react to signal edges:

12642-421: The piping. Signals may be classified into 7 categories. The categories are: Input/output (I/O) devices are slower than the CPU. Therefore, it would slow down the computer if the CPU had to wait for each I/O to finish. Instead, a computer may implement interrupts for I/O completion, avoiding the need for polling or busy waiting. Some computers require an interrupt for each character or word, costing

12771-489: The problems that level-triggered interrupts have with sharing. Service of a low-priority device can be postponed arbitrarily, while interrupts from high-priority devices continue to be received and get serviced. If there is a device that the CPU does not know how to service, which may raise spurious interrupts, it will not interfere with interrupt signaling of other devices. However, it is easy for an edge-triggered interrupt to be missed - for example, when interrupts are masked for

12900-478: The processor clock, and at any time during instruction execution. Consequently, all incoming hardware interrupt signals are conditioned by synchronizing them to the processor clock, and acted upon only at instruction execution boundaries. In many systems, each device is associated with a particular IRQ signal. This makes it possible to quickly determine which hardware device is requesting service, and to expedite servicing of that device. On some older systems, such as

13029-458: The processor commands it to do so, typically after the device has been serviced. The processor samples the interrupt input signal during each instruction cycle. The processor will recognize the interrupt request if the signal is asserted when sampling occurs. Level-triggered inputs allow multiple devices to share a common interrupt signal via wired-OR connections. The processor polls to determine which devices are requesting service. After servicing

13158-511: The program to be restarted with no loss of continuity. A fault is restartable as well but is tied to the synchronous execution of an instruction - the return address points to the faulting instruction. A trap is similar to a fault except that the return address points to the instruction to be executed after the trapping instruction; one prominent use is to implement system calls . An abort is used for severe errors, such as hardware errors and illegal values in system tables, and often does not allow

13287-672: The programmer or the user with the perception that there is a much larger amount of RAM in the computer than is really there. Interrupt Interrupts are commonly used by hardware devices to indicate electronic or physical state changes that require time-sensitive attention. Interrupts are also commonly used to implement computer multitasking and system calls , especially in real-time computing . Systems that use interrupts in these ways are said to be interrupt-driven. Hardware interrupts were introduced as an optimization, eliminating unproductive waiting time in polling loops , waiting for external events. The first system to use this approach

13416-472: The proposal was funded. In particular, they evaluated candidate computers from Bendix , GE , and IBM , and settled upon the GE-225 system paired with a DATANET-30 communications processor. This two-processor approach was unorthodox, and Kemeny later recalled: "At that time, many experts at GE and elsewhere, tried to convince us that the route of the two-computer solution was wasteful and inefficient." In essence,

13545-490: The real-time part will complete the set-up during the next real-time period. The spare-time portion carries out the spare-time tasks, which include mainly disc operations and certain teletype operations. In the GE-235 part there is resident compiler system that acts as a translator, and a resident executive routine to manage the disc input-output operations and to perform other functions. The executive system permits simultaneous use of

13674-418: The remote side excites the gate beyond a threshold, thus no negotiated speed is required. Each has its speed versus distance advantages. A trigger, generally, is the method in which excitation is detected: rising edge, falling edge, threshold ( oscilloscope can trigger a wide variety of shapes and conditions). Triggering for software interrupts must be built into the software (both in OS and app). A 'C' app has

13803-498: The reverse is true, and a set bit disables the interrupt. When the interrupt is disabled, the associated interrupt signal may be ignored by the processor, or it may remain pending. Signals which are affected by the mask are called maskable interrupts . Some interrupt signals are not affected by the interrupt mask and therefore cannot be disabled; these are called non-maskable interrupts (NMIs). These indicate high-priority events which cannot be ignored under any circumstances, such as

13932-481: The same line" can be raised. First is by exclusive conduction (switching) or exclusive connection (to pins). Next is by bus (all connected to the same line listening): cards on a bus must know when they are to talk and not talk (i.e., the ISA bus). Talking can be triggered in two ways: by accumulation latch or by logic gates. Logic gates expect a continual data flow that is monitored for key signals. Accumulators only trigger when

14061-418: The same operating system— OS/360 —which consisted of millions of lines of assembly language that had thousands of bugs . The OS/360 also was the first popular operating system to support multiprogramming , such that the CPU could be put to use on one job while another was waiting on input/output (I/O). Holding multiple jobs in memory necessitated memory partitioning and safeguards against one job accessing

14190-501: The second trimester of the freshman mathematics class to include a requirement for writing and debugging four Dartmouth BASIC programs. By 1968, more than 80% of Dartmouth students had experience in computer programming. 80 classes included "official" computer use, including those in engineering, classics, geography, sociology, and Spanish; that students in the Tuck School of Business and social sciences, not mathematics or engineering, were

14319-400: The signal number (in mnemonic format) to be sent. (The abrasive name of kill was chosen because early implementations only terminated the process.) In Unix-like operating systems, signals inform processes of the occurrence of asynchronous events. To communicate asynchronously, interrupts are required. One reason a process needs to asynchronously communicate to another process solves

14448-400: The size of the machine needed. The different CPUs often need to send and receive messages to each other; to ensure good performance, the operating systems for these machines need to minimize this copying of packets . Newer systems are often multiqueue —separating groups of users into separate queues —to reduce the need for packet copying and support more concurrent users. Another technique

14577-406: The system after no longer being required to. Kemeny—by then the university president—wrote in a 1971 brochure describing the system that just as a student could enter Baker Memorial Library and borrow a book without asking permission or explaining his purpose, "any student may walk into Kiewit Computation Center, sit down at a console, and use the time-sharing system. No one will ask if he is solving

14706-442: The system and may also include accounting software for cost allocation of processor time , mass storage , peripherals, and other resources. For hardware functions such as input and output and memory allocation , the operating system acts as an intermediary between programs and the computer hardware, although the application code is usually executed directly by the hardware and frequently makes system calls to an OS function or

14835-816: The system each year. The off-campus Dartmouth Educational Time-Sharing Network included users with 79 terminals at 30 high schools and 20 universities, including Middlebury College , Phillips Andover , Mount Holyoke College , Goddard College , the United States Merchant Marine Academy , the United States Naval Academy , Bates College , the Dartmouth Club of New York, and a Dartmouth affiliate in Jersey City, New Jersey , sharing DTSS with Dartmouth people. The system allowed email-type messages to be passed between users and real-time chat via

14964-475: The system's memory address space . In systems on a chip (SoC) implementations, interrupts come from different blocks of the chip and are usually aggregated in an interrupt controller attached to one or several processors (in a multi-core system). Multiple devices may share an edge-triggered interrupt line if they are designed to. The interrupt line must have a pull-down or pull-up resistor so that when not actively driven it settles to its inactive state, which

15093-400: The teletype lines. As characters are completed, the real-time part collects them into messages and, when a "return" character is encountered, interprets the message. If it is a line in the program, nothing is done. If the message is a command, a spare-time task to start carrying out the command is set up and inserted in the spare-time list. If there is not enough time to complete this setting-up,

15222-560: The terminal units for the Dartmouth Timesharing system. IDE commands included These commands were often believed to be part of the BASIC language by users, but in fact they were part of the time sharing system and were also used when preparing ALGOL or FORTRAN programs via the DTSS terminals. Kemeny and Kurtz had originally hoped that GE would enter into a research partnership, and to that end Kurtz and student Anthony Knapp authored

15351-472: The timeout signal from a watchdog timer . With regard to SPARC , the Non-Maskable Interrupt (NMI), despite having the highest priority among interrupts, can be prevented from occurring through the use of an interrupt mask. One failure mode is when the hardware does not generate the expected interrupt for a change in state, causing the operating system to wait indefinitely. Depending on the details,

15480-430: The user, and beginning with a line number, was added to the program, replacing any previously stored line with the same number; anything else was taken as a command and immediately executed. Lines which consisted solely of a line number weren't stored but did remove any previously stored line with the same number. This method of editing provided a simple and easy to use service that allowed large numbers of teleprinters as

15609-468: The workload in servicing interrupts grows in proportion to the square of the number of devices. It is therefore preferred to spread devices evenly across the available interrupt lines. Shortage of interrupt lines is a problem in older system designs where the interrupt lines are distinct physical conductors. Message-signaled interrupts, where the interrupt line is virtual, are favored in new system architectures (such as PCI Express ) and relieve this problem to

15738-473: The world. Middleware , an additional software layer between the operating system and applications, is often used to improve consistency. Although it functions similarly to an operating system, it is not a true operating system. Embedded operating systems are designed to be used in embedded computer systems , whether they are internet of things objects or not connected to a network. Embedded systems include many household appliances. The distinguishing factor

15867-446: Was completely different internally from the earlier DTSS, but provided a near-identical user interface to enable a smooth transition for users and course materials. The 635 version provided interactive time-sharing to up to nearly 300 simultaneous users in the 1970s, a very large number at the time, and operated at eleven commercial and academic sites in the US, Canada and Europe. As it evolved in

15996-401: Was in support of multi-user conferences, which behaved somewhat like conference phone calls, and were implemented entirely as user-space application programs. As mentioned above, Hanover High School was connected to DTSS from the system's beginning. Over the next decade, many other high schools and colleges were connected to DTSS via the Kiewit Network, named for Peter Kiewit, donor of funds for

16125-432: Was inspired by a PDP-1 -based time-sharing system at Bolt, Beranek and Newman , there is no evidence that this is true. In 1962, Kemeny and Kurtz submitted a proposal for the development of a new time-sharing system to NSF (which was ultimately funded in 1964). They had sufficient assurance that both Dartmouth and NSF would support the system that they signed a contract with GE and began preliminary work in 1963, before

16254-493: Was replaced with a faster GE-235 computer with minimal issues. By summer of 1965, the system could support forty simultaneous users. A Dartmouth document from October 1964, later revised by GE, describes the overall DTSS architecture: The program in the Datanet-30 is divided into two parts, a real-time part and a spare-time part. The real-time part is entered via clock-controlled interrupt 110 times per second in order to scan

16383-520: Was the DYSEAC , completed in 1954, although earlier systems provided error trap functions. The UNIVAC 1103A computer is generally credited with the earliest use of interrupts in 1953. Earlier, on the UNIVAC I (1951) "Arithmetic overflow either triggered the execution of a two-instruction fix-up routine at address 0, or, at the programmer's option, caused the computer to stop." The IBM 650 (1954) incorporated

16512-406: Was the first popular computer to use a graphical user interface (GUI). The GUI proved much more user friendly than the text-only command-line interface earlier operating systems had used. Following the success of Macintosh, MS-DOS was updated with a GUI overlay called Windows . Windows later was rewritten as a stand-alone operating system, borrowing so many features from another ( VAX VMS ) that

16641-432: Was used in large freshman courses. Kurtz approached Kemeny in either 1961 or 1962, with the following proposal: all Dartmouth students would have access to computing, it should be free and open-access, and this could be accomplished by creating a time-sharing system (which Kurtz had learned about from colleague John McCarthy at MIT , who suggested "why don't you guys do timesharing?"). Although it has been stated that DTSS

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