113-503: Multiple Virtual Storage , more commonly called MVS , is the most commonly used operating system on the System/370 , System/390 and IBM Z IBM mainframe computers . IBM developed MVS, along with OS/VS1 and SVS , as a successor to OS/360 . It is unrelated to IBM's other mainframe operating system lines, e.g., VSE , VM , TPF . First released in 1974, MVS was extended by program products with new names multiple times, retaining
226-615: A Cross-system Coupling Facility (XCF) and a hardware component called a Hardware Coupling Facility (CF or Integrated Coupling Facility, ICF, if co-located on the same mainframe hardware). Multiple sysplexes can be joined via standard network protocols such as IBM's proprietary Systems Network Architecture (SNA) or, more recently, via TCP/IP . The z/OS operating system (MVS' most recent descendant) also has native support to execute POSIX and Single UNIX Specification applications. The support began with MVS/SP V4R3, and IBM has obtained UNIX 95 certification for z/OS V1R2 and later. The system
339-428: 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
452-525: A "current directory" concept), and RACF supports setting up access controls based on filename patterns, analogous to access controls on directories on other platforms. As with other members of the OS family, MVS' data sets are record-oriented . MVS inherited three main types from its predecessors: Sequential and ISAM datasets could store either fixed-length or variable length records, and all types could occupy more than one disk volume. All of these are based on
565-576: A 4 KiB granularity (for SVS), and the requests came out of a 16MiB address space even if physical storage was smaller. As in OS/360 MVT, TSO users in SVS are assigned to a TSO region during login processing and competed with other users assigned to the same region, with essentially the same swap-in and swap-out logic as TSO in MVT. In the mid-1970s IBM introduced MVS, which not only supported virtual storage that
678-645: 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
791-476: A control program and given processing cycles. Unlike a single-programming operating system, these systems maximize the use of the processing potential by dividing processing cycles among the instructions associated with several different concurrently running programs. This way, the control program does not have to wait for the I/O operation to complete before proceeding. By executing the instructions for multiple programs,
904-585: 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
1017-453: A hierarchy of error-handling programs, in system (kernel/'privileged') mode, called Functional Recovery Routines, and in user ('task' or 'problem program') mode, called "ESTAE" (Extended Specified Task Abnormal Exit routines) that are invoked in case the system detected an error (hardware processor or storage error, or software error). Each recovery routine made the 'mainline' function reinvokable, captured error diagnostic data sufficient to debug
1130-468: A hierarchy whose levels are separated with dots, e.g. "DEPT01.SYSTEM01.FILE01". Each level in the hierarchy can be up to eight characters long. The total filename length is a maximum of 44 characters including dots. By convention, the components separated by the dots are used to organize files similarly to directories in other operating systems. For example, there are utility programs that performed similar functions to those of Windows Explorer (but without
1243-466: A high speed communication system ( Gigabit Ethernet is common). A Linux Beowulf cluster is an example of a loosely coupled system. Tightly coupled systems perform better and are physically smaller than loosely coupled systems, but have historically required greater initial investments and may depreciate rapidly; nodes in a loosely coupled system are usually inexpensive commodity computers and can be recycled as independent machines upon retirement from
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#17327727872361356-484: 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,
1469-597: A large partition. If there were two large programs ready to run, one would have to wait until the other finished and vacated the large partition. OS/360 R19 added MFT sub-tasking ( multitasking ), the ability for a job to dynamically create new tasks with the ATTACH macro. OS/360 MVT (Multiprogramming with a Variable number of Tasks) was an enhancement that further refined memory use. Instead of using fixed-size memory partitions, MVT allocates memory to regions for job steps as needed, provided enough contiguous physical memory
1582-442: 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
1695-628: A major design jump, to assume that despite the very best software development and testing techniques, that 'problems WILL occur.' This profound assumption was pivotal in adding great percentages of fault-tolerance code to the system and likely contributed to the system's success in tolerating software and hardware failures. Statistical information is hard to come by to prove the value of these design features (how can you measure 'prevented' or 'recovered' problems?), but IBM has, in many dimensions, enhanced these fault-tolerant software recovery and rapid problem resolution features, over time. This design specified
1808-447: 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,
1921-549: A master/slave multiprocessor system of microprocessors is the Tandy/Radio Shack TRS-80 Model 16 desktop computer which came out in February 1982 and ran the multi-user/multi-tasking Xenix operating system, Microsoft's version of UNIX (called TRS-XENIX). The Model 16 has two microprocessors: an 8-bit Zilog Z80 CPU running at 4 MHz, and a 16-bit Motorola 68000 CPU running at 6 MHz. When
2034-570: A number of free Incremental Change Releases (ICRs) and Selectable Units (SUs) and chargeable program products and field developed programs that IBM eventually bundled as part of z/OS. These include: In the late seventies and early eighties IBM announced: DF/DS added new device support, and IBM announced that it would no longer add device support to the free base. DF/EF added the Improved Catalog Structure (ICF) as an alternative to VSAM catalogs and Control Volumes (CVOLs), but it
2147-478: A number of ways, including asymmetric multiprocessing (ASMP), non-uniform memory access (NUMA) multiprocessing, and clustered multiprocessing. In a master/slave multiprocessor system, the master CPU is in control of the computer and the slave CPU(s) performs assigned tasks. The CPUs can be completely different in terms of speed and architecture. Some (or all) of the CPUs can share a common bus, each can also have
2260-455: 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
2373-541: A private bus (for private resources), or they may be isolated except for a common communications pathway. Likewise, the CPUs can share common RAM and/or have private RAM that the other processor(s) cannot access. The roles of master and slave can change from one CPU to another. Two early examples of a mainframe master/slave multiprocessor are the Bull Gamma 60 and the Burroughs B5000 . An early example of
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#17327727872362486-503: 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
2599-408: 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
2712-440: 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
2825-479: A result of later hardware enhancements one instance of an operating system (either MVS, or VM with guests, or other) could also occupy a Logical Partition (LPAR) instead of an entire physical system. Multiple MVS instances can be organized and collectively administered in a structure called a systems complex or sysplex , introduced in September, 1990. Instances interoperate through a software component called
2938-477: A result, MVS was able to address the business problems brought on by the need to process large amounts of data. Multiprocessing systems are either loosely coupled, which means that each computer has access to a common workload, or tightly coupled , which means that the computers share the same real storage and are controlled by a single copy of the operating system . MVS retained both the loosely coupled multiprocessing of Attached Support Processor (ASP) and
3051-424: A session to create diagnostic procedures, or invoke already-stored procedures. The procedures trapped special events, such as the loading of a program, device I/O, system procedure calls, and then triggered the activation of the previously defined procedures. These procedures, which could be invoked recursively, allowed for reading and writing of data, and alteration of instruction flow. Program Event Recording hardware
3164-502: A shared virtual area used for various purposes, including inter-job communication. IBM promised that application areas would always be at least 8MB. This made MVS the perfect solution for business problems that resulted from the need to run more applications. MVS maximized processing potential by providing multiprogramming and multiprocessing capabilities. Like its MVT and OS/VS2 SVS predecessors, MVS supported multiprogramming ; program instructions and associated data are scheduled by
3277-470: 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
3390-402: A single virtual address space , shared by all jobs. OS/VS1 is OS/360 MFT within a single virtual address space; OS/VS2 SVS was OS/360 MVT within a single virtual address space. So OS/VS1 and SVS in principle had the same disadvantages as MFT and MVT, but the impacts are less severe because jobs and operators could request much larger partitions with a 2 KiB granularity (for OS/VS1) or regions with
3503-402: 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
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3616-683: A user can allocate a Unix file as though it were a dataset, with some restrictions. The Hierarchical File System (HFS) (not to be confused with Apple's Hierarchical File System ) uses a unique type of dataset, while the newer z/OS File System (zFS) (not to be confused with Sun's ZFS ) uses a VSAM Linear Data Set (LDS). Programs running on network-connected computers (such as the IBM AS/400 ) can use local data management interfaces to transparently create, manage, and access VSAM record-oriented files by using client-server products implemented according to Distributed Data Management Architecture (DDM). DDM
3729-417: 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
3842-594: A valid reportable failure. Also, if a recovery routine failed to collect significant diagnostic data such that the original problem was solvable by data collected by that recovery routine, IBM standards dictated that this fault was reportable and required repair. Thus, IBM standards, when rigorously applied, encouraged continuous improvement. IBM continued to support the major serviceability tool Dynamic Support System (DSS) that it had introduced in OS/VS1 and OS/VS2 Release 1. This interactive facility could be invoked to initiate
3955-453: 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
4068-421: Is command line , although facilities, such as ISPF , were added later for form-driven interfaces. MVS took a major step forward in fault-tolerance, built on the earlier STAE facility, that IBM called software recovery . IBM decided to do this after years of practical real-world experience with MVT in the business world. System failures were now having major impacts on customer businesses, and IBM decided to take
4181-562: 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
4294-428: 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 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 ,
4407-484: 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
4520-501: Is also the base architecture for the MVS DB2 server that implements Distributed Relational Database Architecture (DRDA). MVS includes a facility called Virtual I/O (VIO), with which temporary datasets can be stored in simulated tracks on the paging datasets, eliminating the overhead of allocation but adding some processing overhead. In addition to new functionality that IBM added with releases and sub-releases of OS/VS2, IBM provided
4633-455: Is available. This is a significant advance over MFT's memory management, but has some weaknesses: if a job allocates memory dynamically (as most sort programs and database management systems do), the programmers has to estimate the job's maximum memory requirement and pre-define it for MVT. A job step that contains a mix of small and large programs wastes memory while the small programs run. Most seriously, memory can become fragmented , i.e.,
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4746-422: 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
4859-399: Is generally used to denote that scenario. Other authors prefer to refer to the operating system techniques as multiprogramming and reserve the term multiprocessing for the hardware aspect of having more than one processor. The remainder of this article discusses multiprocessing only in this hardware sense. In Flynn's taxonomy , multiprocessors as defined above are MIMD machines. As
4972-736: Is now possible to run the MVS 3.8j release in mainframe emulators for free, such as the Hercules Emulator . MVS/370 is a generic term for all versions of the MVS operating system prior to MVS/XA. The System/370 architecture, at the time MVS was released, supported only 24-bit virtual addresses, so the MVS/370 operating system architecture is based on a 24-bit address. Because of this 24-bit address length, programs running under MVS/370 are each given 16 MB of contiguous virtual storage. Operating system An operating system ( OS )
5085-443: 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
5198-411: Is sometimes contrasted with multitasking , which may use just a single processor but switch it in time slices between tasks (i.e. a time-sharing system ). Multiprocessing however means true parallel execution of multiple processes using more than one processor. Multiprocessing doesn't necessarily mean that a single process or task uses more than one processor simultaneously; the term parallel processing
5311-499: 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,
5424-473: 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
5537-435: 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 ,
5650-556: Is typically used in business and banking, and applications are often written in COBOL . COBOL programs were traditionally used with transaction processing systems like IMS and CICS . For a program running in CICS, special EXEC CICS statements are inserted in the COBOL source code. A preprocessor (translator) replaces those EXEC CICS statements with the appropriate COBOL code to call CICS before
5763-542: 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
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#17327727872365876-529: The GUI and usually in batch processing mode) - adding, renaming or deleting new elements and reporting all the contents of a specified element. However, unlike in many other systems, these levels are not usually actual directories but just a naming convention (like the original Macintosh File System , where folder hierarchy was an illusion maintained by the Finder). TSO supports a default prefix for files (similar to
5989-504: 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
6102-500: The VTOC disk structure. Early IBM database management systems used various combinations of ISAM and BDAM datasets - usually BDAM for the actual data storage and ISAM for indexes. In the early 1970s IBM's virtual memory operating systems introduced a new file management component, VSAM , which provided similar facilities: These VSAM formats became the basis of IBM's database management systems , IMS/VS and DB2 - usually ESDS for
6215-408: The interactive time-sharing interface, which was mainly used to run development tools and a few end-user information systems. ISPF is a TSO application for users on 3270-family terminals (and later, on VM as well), which allows the user to accomplish the same tasks as TSO's command line but in a menu and form oriented manner, and with a full screen editor and file browser. TSO's basic interface
6328-498: 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 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
6441-420: 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
6554-466: The 68000 CPU. The Z-80 can be used to do other tasks. The earlier TRS-80 Model II , which was released in 1979, could also be considered a multiprocessor system as it had both a Z-80 CPU and an Intel 8021 microcontroller in the keyboard. The 8021 made the Model II the first desktop computer system with a separate detachable lightweight keyboard connected with by a single thin flexible wire, and likely
6667-410: 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
6780-474: 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
6893-665: The Xeon processors via a common pipe and the Opteron processors via independent pathways to the system RAM . Chip multiprocessors, also known as multi-core computing, involves more than one processor placed on a single chip and can be thought of the most extreme form of tightly coupled multiprocessing. Mainframe systems with multiple processors are often tightly coupled. Loosely coupled multiprocessor systems (often referred to as clusters ) are based on multiple standalone relatively low processor count commodity computers interconnected via
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#17327727872367006-406: The actual data storage and KSDS for indexes. VSAM also included a catalog component used for user catalogs and MVS' master catalog. Partitioned data sets (PDS) are sequential data sets subdivided into "members" that could each be processed as sequential files in their own right (like a folder in a file system). The most important use of PDSes was for program libraries - system administrators used
7119-538: 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
7232-511: The bus level. These CPUs may have access to a central shared memory (SMP or UMA ), or may participate in a memory hierarchy with both local and shared memory (SM)( NUMA ). The IBM p690 Regatta is an example of a high end SMP system. Intel Xeon processors dominated the multiprocessor market for business PCs and were the only major x86 option until the release of AMD 's Opteron range of processors in 2004. Both ranges of processors had their own onboard cache but provided access to shared memory;
7345-425: The causing problem, and either 'retried' (reinvoke the mainline) or 'percolated' (escalated error processing to the next recovery routine in the hierarchy). Thus, with each error the system captured diagnostic data, and attempted to perform a repair and keep the system up. The worst thing possible was to take down a user address space (a 'job') in the case of unrepaired errors. Though it was an initial design point, it
7458-451: The cluster. Power consumption is also a consideration. Tightly coupled systems tend to be much more energy-efficient than clusters. This is because a considerable reduction in power consumption can be realized by designing components to work together from the beginning in tightly coupled systems, whereas loosely coupled systems use components that were not necessarily intended specifically for use in such systems. Loosely coupled systems have
7571-674: The computer is able to switch back and forth between active and inactive programs. Early editions of MVS (mid-1970s) are among the first of the IBM OS series to support multiprocessor configurations, though the M65MP variant of OS/360 running on 360 Models 65 and 67 had provided limited multiprocessor support. The 360 Model 67 had also hosted the multiprocessor capable TSS/360 , MTS and CP-67 operating systems. Because multiprocessing systems can execute instructions simultaneously, they offer greater processing power than single-processing system. As
7684-453: 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
7797-518: The definition of multiprocessing can vary with context, mostly as a function of how CPUs are defined ( multiple cores on one die , multiple dies in one package , multiple packages in one system unit , etc.). According to some on-line dictionaries, a multiprocessor is a computer system having two or more processing units (multiple processors) each sharing main memory and peripherals, in order to simultaneously process programs. A 2009 textbook defined multiprocessor system similarly, but noting that
7910-471: 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
8023-422: 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
8136-404: The fact that processing progresses despite an error can overwrite the tracks. Early data capture at the time of the error maximizes debugging, and facilities exist for the recovery routines (task and system mode, both) to do this. IBM included additional criteria for a major software problem that required IBM service. If a mainline component failed to initiate software recovery, that was considered
8249-741: The first keyboard to use a dedicated microcontroller, both attributes that would later be copied years later by Apple and IBM. In multiprocessing, the processors can be used to execute a single sequence of instructions in multiple contexts ( single instruction, multiple data or SIMD, often used in vector processing ), multiple sequences of instructions in a single context ( multiple instruction, single data or MISD, used for redundancy in fail-safe systems and sometimes applied to describe pipelined processors or hyper-threading ), or multiple sequences of instructions in multiple contexts ( multiple instruction, multiple data or MIMD). Tightly coupled multiprocessor systems contain multiple CPUs that are connected at
8362-410: 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
8475-493: 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
8588-418: 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
8701-466: The information to one program - each collecting program created a new generation of the file and the final program read the whole group as a single sequential file (by not specifying a generation in the JCL ). Modern versions of MVS (e.g., z/OS) use datasets as containers for Unix filesystems along with facilities for partially integrating them. That is, Unix programs using fopen() can access an MVS dataset and
8814-404: 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
8927-431: 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
9040-497: The main PDS as a way to allocate disk space to a project and the project team then created and edited the members. Other uses of PDSs are libraries of frequently used job control procedures (PROCs), and "copy books" of programming language statements such as record definitions used by several programs. Generation Data Groups (GDGs) are groups of like named data sets, which can be referenced by absolute generation number, or by an offset from
9153-400: 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
9266-461: The memory not used by current jobs could be divided into uselessly small chunks between the areas used by current jobs, and the only remedy was to wait until some current jobs finished before starting any new ones. In the early 1970s IBM sought to mitigate these difficulties by introducing virtual memory (which IBM called "virtual storage"), which allowed programs to request address spaces larger than physical memory. The original implementations had
9379-443: The most recent generation. They were originally designed to support grandfather-father-son backup procedures - if a file was modified, the changed version became the new "son", the previous "son" became the "father", the previous "father" became the "grandfather" and the previous "grandfather" was deleted. But one could set up GDGs with more than 3 generations and some applications used GDGs to collect data from several sources and feed
9492-408: 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
9605-436: The new system MVS from the start, and IBM continued to use the term MVS in the naming of later major versions such as MVS/XA. OS/360 MFT (Multiprogramming with a Fixed number of Tasks) provides multiprogramming : several memory partitions , each of a fixed size, are set up when the operating system is installed and when the operator redefines them. For example, there could be a small partition, two medium partitions, and
9718-408: 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
9831-420: 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 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
9944-521: The operating system component JES3 allowed managing the whole group from one console. This provided greater resilience and let operators decide which processor should run which jobs from a central job queue. MVS JES3 gave users the opportunity to network together two or more data processing systems via shared disks and Channel-to-Channel Adapters (CTCA's). This capability eventually became available to JES2 users as Multi-Access SPOOL (MAS). MVS originally supported 24-bit addressing (i.e., up to 16MB). As
10057-1108: The past with a 3270 terminal, is now done through the Hardware Management Console (HMC) and, increasingly, Web interfaces. Operator consoles are provided through 2074 emulators, so you are unlikely to see any S/390 or zSeries processor with a real 3270 connected to it. The native character encoding scheme of MVS and its peripherals is EBCDIC , but the TR instruction made it easy to translate to other 7- and 8-bit codes. Over time IBM added hardware-accelerated services to perform translation to and between larger codes, hardware-specific service for Unicode transforms and software support of, e.g., ASCII , ISO/IEC 8859 , UTF-8 , UTF-16 , and UTF-32 . The software translation services take source and destination code pages as inputs. Files, other than Unix files, are properly called data sets in MVS. Names of those files are organized in catalogs that are VSAM files themselves. Data set names (DSNs, mainframe term for filenames) are organized in
10170-474: The performance-sensitive ones, in particular not the Input/Output Supervisor (IOS). IBM's use of "OS/VS2" emphasized upwards compatibility: application programs that ran under MVT did not even need recompiling to run under MVS. The same Job Control Language files could be used unchanged; utilities and other non-core facilities like TSO ran unchanged. IBM and users almost unanimously called
10283-421: 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
10396-441: The processors may share "some or all of the system’s memory and I/O facilities"; it also gave tightly coupled system as a synonymous term. At the operating system level, multiprocessing is sometimes used to refer to the execution of multiple concurrent processes in a system, with each process running on a separate CPU or core, as opposed to a single process at any one instant. When used with this definition, multiprocessing
10509-668: The program is compiled — not altogether unlike SQL used to call DB2 . Applications can also be written in other languages such as C , C++ , Java , assembly language , FORTRAN , BASIC , RPG , and REXX . Language support is packaged as a common component called "Language Environment" or "LE" to allow uniform debugging, tracing, profiling, and other language independent functions. MVS systems are traditionally accessed by 3270 terminals or by PCs running 3270 emulators. However, many mainframe applications these days have custom web or GUI interfaces. The z/OS operating system has built-in support for TCP/IP . System management, done in
10622-450: The programmer or the user with the perception that there is a much larger amount of RAM in the computer than is really there. Multiprocessing Multiprocessing is the use of two or more central processing units (CPUs) within a single computer system . The term also refers to the ability of a system to support more than one processor or the ability to allocate tasks between them. There are many variations on this basic theme, and
10735-418: 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
10848-619: 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
10961-413: The shared virtual area, but this imposed a significant overhead since all such communications had transmit via the operating system.) The main user interfaces to MVS are: Job Control Language (JCL), which was originally designed for batch processing but from the 1970s onwards was also used to start and allocate resources to long-running interactive jobs such as CICS ; and TSO (Time Sharing Option),
11074-400: 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
11187-400: 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
11300-739: The symmetry (or lack thereof) in a given system. For example, hardware or software considerations may require that only one particular CPU respond to all hardware interrupts, whereas all other work in the system may be distributed equally among CPUs; or execution of kernel-mode code may be restricted to only one particular CPU, whereas user-mode code may be executed in any combination of processors. Multiprocessing systems are often easier to design if such restrictions are imposed, but they tend to be less efficient than systems in which all CPUs are utilized. Systems that treat all CPUs equally are called symmetric multiprocessing (SMP) systems. In systems where all CPUs are not equal, system resources may be divided in
11413-502: The system is booted, the Z-80 is the master and the Xenix boot process initializes the slave 68000, and then transfers control to the 68000, whereupon the CPUs change roles and the Z-80 becomes a slave processor responsible for all I/O operations including disk, communications, printer and network, as well as the keyboard and integrated monitor, while the operating system and applications run on
11526-420: The term "multiprocessor" normally refers to tightly coupled systems in which all processors share memory, multiprocessors are not the entire class of MIMD machines, which also contains message passing multicomputer systems. In a multiprocessing system, all CPUs may be equal, or some may be reserved for special purposes. A combination of hardware and operating system software design considerations determine
11639-523: The term MVS in the nomenclature: and then extended At first IBM described MVS as simply a new release of OS/VS2 , but it is, in fact a major rewrite. OS/VS2 release 1 is an upgrade of OS/360 MVT that retained most of the original code and, like MVT, is mainly written in assembly language . The MVS core is almost entirely written in Assembler XF , although a few modules were written in PL/S , but not
11752-465: The tightly coupled multiprocessing of OS/360 Model 65 Multiprocessing . In tightly coupled systems, two CPUs shared concurrent access to the same memory (and copy of the operating system) and peripherals, providing greater processing power and a degree of graceful degradation if one CPU failed. In loosely coupled configurations each of a group of processors (single and / or tightly coupled) had its own memory and operating system but shared peripherals and
11865-566: The underlying hardware progressed, it supported 31-bit (XA and ESA; up to 2048MB) and now (as z/OS) 64-bit addressing. The most significant motives for the rapid upgrade to 31-bit addressing were the growth of large transaction-processing networks, mostly controlled by CICS , which ran in a single address space—and the DB2 relational database management system needed more than 8MB of application address space to run efficiently. (Early versions were configured into two address spaces that communicated via
11978-473: 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
12091-480: Was larger than the available real storage, as did SVS, but also allowed an indefinite number of applications to run in different address spaces. Two concurrent programs might try to access the same virtual memory address, but the virtual memory system redirected these requests to different areas of physical memory. Each of these address spaces consisted of three areas: an operating system (one instance shared by all jobs), an application area unique for each application, and
12204-589: Was not until the most recent MVS version (z/OS), that recovery program was not only guaranteed its own recovery routine, but each recovery routine now has its own recovery routine. This recovery structure was embedded in the basic MVS control program, and programming facilities are available and used by application program developers and 3rd party developers. Practically, the MVS software recovery made problem debugging both easier and more difficult. Software recovery requires that programs leave 'tracks' of where they are and what they are doing, thus facilitating debugging—but
12317-713: Was optional, but MVS/Extended Architecture Data Facility Product (5665-284) was a corequisite for MVS/SP Version 2 (MVS/XA). In addition to enhancing data management facilities, DFP replaced free versions of the linkage editor and utilities. DFP is no longer available as a separate product, but has become part of Data Facility Storage Management Subsystem , under the name DFSMSdfp . MVS has now evolved into z/OS; older MVS releases are no longer supported by IBM and, since 2007, only 64-bit z/OS releases are supported. z/OS supports running older 24-bit and 31-bit MVS applications alongside newer 64-bit applications. MVS releases up to 3.8j (24-bit, released in 1981) were freely available and it
12430-508: Was performed by the enhancement of the diagnostic SLIP command with the introduction of the PER support (SLIP/Per) in SU 64/65 (1978). Multiple copies of MVS (or other IBM operating systems) could share the same machine if that machine was controlled by VM/370 . In this case VM/370 was the real operating system, and regarded the "guest" operating systems as applications with unusually high privileges. As
12543-401: Was riddled with reliability problems. When IBM announced MVS/SP Version 2 (MVS/XA), it also announced Data Facility Product™ (DFP™) as a replacement for and upgrade to the other five products above, which it said would be withdrawn from marketing, effective December 1, 1984. DFP/370 Release 1 (program number 5665-295), announced June 7, 1983, was for MVS/SP Version 1, MVS/SE and OS/VS2 R3.8, and
12656-406: 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
12769-495: Was used. IBM dropped support for DSS with Selectable Unit 7 (SU7), an update to OS/VS2 Release 3.7 required by the program product OS/VS2 MVS/System Extensions (MVS/SE), Program Number 5740-XEl. The User group SHARE passed a requirement that IBM reinstate DSS, and IBM provided a PTF to allow use of DSS after MVS/SE was installed. IBM again dropped support for DSS with SU64, an update to OS/VS2 Release 3.8 required by Release 2 of MVS/SE. Program-Event Recording (PER) exploitation
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