MVS
Encyclopedia
Multiple Virtual Storage, more commonly called MVS, was the most commonly used operating system
on the System/370
and System/390 IBM mainframe computers. It was developed by IBM
, but is unrelated to IBM's other mainframe operating systems, e.g., VSE, VM
.
First released in 1974, MVS was extended by program products with new names multiple times, first to MVS/SE (System Extension), next to MVS/SP (System Product) Version 1, next to MVS/XA (eXtended Architecture), next to MVS/ESA (Enterprise Systems Architecture), next to OS/390
and finally to z/OS
(when 64-bit
support was added with the zSeries
models). IBM added Unix support (originally called OPEN EDITION) in MVS/SP V4.3 and has obtained POSIX and Unix certifications at several different levels. MVS's core remains fundamentally the same operating system. By design, programs written for MVS run on z/OS without modification.
At first IBM described MVS as simply a new release of OS/VS2
, but it was, in fact a major rewrite. OS/VS2 release 1 was an upgrade of OS/360 MVT that retained most of the original code and, like MVT, were mainly written in Assembler
. The MVS core was almost entirely written in Assembler XF, although a few modules were written in PL/S, but not 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 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 MVT (Multitasking with a Variable number of Tasks) was an enhancement that further refined memory use. Instead of using fixed-size memory partitions, MVT allocated memory to regions for job steps as needed, provided enough contiguous physical memory was available. This was a significant advance over MFT's memory management, but had some weaknesses: if a job allocated memory dynamically (as most sort
programs and database management system
s do), the programmers had to estimate the job's maximum memory requirement and pre-define it for MVT. A job step that contained a mix of small and large programs wasted memory while the small programs ran. Most seriously, memory could become fragmented
, i.e., 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 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 space
s larger than physical memory. The original implementations had a single virtual address space, shared by all jobs. OS/VS1 was 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 were less severe because jobs could request much larger address spaces and the requests came out of a 16 MiB pool even if physical storage was smaller.
In the mid-1970s IBM introduced MVS, which not only supported virtual storage that was larger than the available real storage,Some processors could take more physical storage than the size of a single address space, but still much smaller than the aggregate size of a typical workload's virtual 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 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 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, the computer is able to switch back and forth between active and inactive programs.
Early editions of MVS (mid-1970s) were 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 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)Via Job Entry Subsystem 3 (JES3) and 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 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-Channedl 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 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 8 MB of application address space to run efficiently. (Early versions were configured into two address spaces that communicated via 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 CICS
; and TSO
(Time Sharing Option), 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 is command line, although facilities 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 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, but 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 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 were invoked in case the system detected an error (actually, hardware processor or storage error, or software error). Each recovery routine made the 'mainline' function reinvokable, captured error diagnostic data sufficient to debug 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 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 the fact that processing progresses despite an error can overwrite the tracks. Early date 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 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 introduced an on-demand hypervisor
, a major serviceability tool, called Dynamic Support System (DSS), in the first release of MVS. This facility could be invoked to initiate 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 was used. Due to the overhead of this tool, it was removed from customer-available MVS systems. Program-Event Recording (PER) exploitation 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 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 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
applications.
Files are properly called data set
s in MVS. Names of those files are organized in catalogs that are VSAM files themselves.
The native encoding scheme of MVS and its peripherals is Big Endian EBCDIC
, but over time IBM added hardware-accelerated services to perform translation and support of ASCII
, Little Endian, and Unicode
.
(but without 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 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 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 were 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 the VTOC
disk structure.
Early IBM database management system
s 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 the actual data storage and KSDS for indexes.
VSAM also included a catalog component used for MVS' master catalog.
Partitioned datasets (PDS) were sequential datasets subdivided into "members" that could be processed as sequential files in their own right. The most important use of PDS was for program libraries - system administrators used the main PDS as a way to allocate disk space to a project and the project team then created and edited the members.
Generation Data Groups (GDGs) 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 a lot more than 3 generations and some applications used GDGs to collect data from several sources and feed 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) also support POSIX-compatible "slash" filesystems along with facilities for integrating the two filesystems. That is, the OS can make an MVS dataset appear as a file to a POSIX program or subsystem. These newer filesystems include Hierarchical File System (HFS) (not to be confused with Apple's Hierarchical File System
) and zFS
(not to be confused with Sun's ZFS
).
MVS releases up to 3.8j (24-bit, released in 1981) were freely available and it is now possible to run the MVS 3.8j release in mainframe emulators for free.
prior to MVS/XA.OS/VS2 Release 2 through 3.8, MVS/SE and MVS/SP Version 1 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 megabytes of contiguous virtual storage.
addressable memory area. It also supported a 24-bit legacy addressing mode for older 24-bit applications (i.e. those that stored a 24-bit address in the lower 24 bits of a 32-bit word and utilized the upper 8 bits of that word for other purposes).
.
MVS/ESA OpenEdition: upgrade to Version 4 Release 3 of MVS/ESA announced February 1993 with support for POSIX
and other standards. While the initial release only had National Institute of Standards and Technology
(NIST) certification for Federal Information Processing Standard
(FIPS) 151 compliance, subsequent releases were certified at higher levels and by other organizations, e.g. X/Open and its successor, The Open Group. It included about 1 million new lines of code, which provide an API shell, utilities, and an extended user interface. Works with a hierarchical file system provided by DFSMS (Data Facility System Managed Storage). The shell and utilities are based on Mortice Kerns' InterOpen products. Independent specialists reckon it was over 80% open systems-compliant—more than most Unix systems. DCE2 support announced February 1994, and many application development tools in March 1995. Mid 1995 IBM started to stop referring to OpenEdition as a separate entity, as all the open features became a standard part of vanilla MVS/ESA SP Version 5 Release 1. Under OS/390
, it became Unix System Services, and has kept that name under z/OS
.
and Hitachi
both repeatedly and illegally obtained IBM's MVS source code
and internal documentation in one of the 20th century's most famous cases of industrial espionage
. Fujitsu relied heavily on IBM's code in its MSP mainframe operating system, and likewise Hitachi did the same for its VOS3 operating system. MSP and VOS3 were heavily marketed in Japan, where they still hold a substantial share of the mainframe installed base, but also to some degree in other countries, notably Australia. Even IBM's bugs and documentation misspellings were faithfully copied. IBM cooperated with the U.S. Federal Bureau of Investigation
in a sting operation
, reluctantly supplying Fujitsu and Hitachi with proprietary MVS and mainframe hardware technologies during the course of multi-year investigations culminating in the early 1980s -- investigations which implicated senior company managers and even some Japanese government officials. (Amdahl
was not involved in Fujitsu's theft of IBM's IP; indeed, any communications from Amdahl to Fujitsu were through "Amdahl Only Specifications" which were scrupulously cleansed of any IBM IP or any references to IBM's IP.) Subsequent to the investigations, IBM reached multi-million dollar settlements with both Fujitsu and Hitachi, collecting substantial fractions of both companies' profits for many years (reliable reports are that the settlements exceeded US$500,000,000 ... exceeded half a billion dollars). (The three companies have long since amicably agreed to many joint business ventures. For example, in 2002 IBM and Hitachi collaborated on developing the IBM z800 mainframe model.) Because of this incident, MSP and VOS3 are properly classified as "forks"
of MVS, and many third party software vendors with MVS-compatible products were able to produce MSP- and VOS3-compatible versions with little or no modification.
When IBM introduced its 64-bit
z/Architecture
mainframes in the year 2000, IBM also introduced the 64-bit z/OS operating system, the direct successor to OS/390 and MVS. Fujitsu and Hitachi opted not to license IBM's z/Architecture for their quasi-MVS operating systems and hardware systems, and so MSP and VOS3, while still nominally supported by their vendors, maintain most of MVS's 1980s architectural limitations to the present day. Since z/OS still supports MVS-era applications and technologies -- indeed, z/OS still contains most of MVS's code, albeit greatly enhanced and improved over decades of evolution -- applications (and operational procedures) running on MSP and VOS3 can move to z/OS much more easily than to other operating systems.
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
on the System/370
System/370
The IBM System/370 was a model range of IBM mainframes announced on June 30, 1970 as the successors to the System/360 family. The series maintained backward compatibility with the S/360, allowing an easy migration path for customers; this, plus improved performance, were the dominant themes of the...
and System/390 IBM mainframe computers. It was developed by IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
, but is unrelated to IBM's other mainframe operating systems, e.g., VSE, VM
VM (operating system)
VM refers to a family of IBM virtual machine operating systems used on IBM mainframes System/370, System/390, zSeries, System z and compatible systems, including the Hercules emulator for personal computers. The first version, released in 1972, was VM/370, or officially Virtual Machine Facility/370...
.
First released in 1974, MVS was extended by program products with new names multiple times, first to MVS/SE (System Extension), next to MVS/SP (System Product) Version 1, next to MVS/XA (eXtended Architecture), next to MVS/ESA (Enterprise Systems Architecture), next to OS/390
OS/390
OS/390 is an IBM operating system for the System/390 IBM mainframe computers.OS/390 was introduced in late 1995 in an effort, led by the late Randy Stelman, to simplify the packaging and ordering for the key, entitled elements needed to complete a fully functional MVS operating system package...
and finally to z/OS
Z/OS
z/OS is a 64-bit operating system for mainframe computers, produced by IBM. It derives from and is the successor to OS/390, which in turn followed a string of MVS versions.Starting with earliest:*OS/VS2 Release 2 through Release 3.8...
(when 64-bit
64-bit
64-bit is a word size that defines certain classes of computer architecture, buses, memory and CPUs, and by extension the software that runs on them. 64-bit CPUs have existed in supercomputers since the 1970s and in RISC-based workstations and servers since the early 1990s...
support was added with the zSeries
ZSeries
IBM System z, or earlier IBM eServer zSeries, is a brand name designated by IBM to all its mainframe computers.In 2000, IBM rebranded the existing System/390 to IBM eServer zSeries with the e depicted in IBM's red trademarked symbol, but because no specific machine names were changed for...
models). IBM added Unix support (originally called OPEN EDITION) in MVS/SP V4.3 and has obtained POSIX and Unix certifications at several different levels. MVS's core remains fundamentally the same operating system. By design, programs written for MVS run on z/OS without modification.
At first IBM described MVS as simply a new release of OS/VS2
OS/VS2
Operating System/Virtual Storage 2 is the successor operating system to OS/360 MVT in the OS/360 family.*SVS refers to OS/VS2 Release 1*MVS refers to OS/VS2 Release 2 and later...
, but it was, in fact a major rewrite. OS/VS2 release 1 was an upgrade of OS/360 MVT that retained most of the original code and, like MVT, were mainly written in Assembler
Assembly language
An assembly language is a low-level programming language for computers, microprocessors, microcontrollers, and other programmable devices. It implements a symbolic representation of the machine codes and other constants needed to program a given CPU architecture...
. The MVS core was almost entirely written in Assembler XF, although a few modules were written in PL/S, but not the performance-sensitive ones, in particular not the Input/Output Supervisor (IOS
Input/Output Supervisor
The Input/Output Supervisor is that portion of the IBM mainframe operating system control program which issues the privileged I/O instructions and supervises the resulting I/O interruptions for any program which requests I/O device operations until the normal or abnormal conclusion of those...
). 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
Job Control Language
Job Control Language is a scripting language used on IBM mainframe operating systems to instruct the system on how to run a batch job or start a subsystem....
files could be used unchanged; utilities and other non-core facilities like TSO
Time Sharing Option
In computing, Time Sharing Option is an interactive time-sharing environment for IBM mainframe operating systems, including OS/360 MVT, OS/VS2 , MVS, OS/390, and z/OS.- Overview :TSO fulfills a similar purpose to Unix login sessions...
ran unchanged. IBM and users almost unanimously called 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.
Evolution of MVS
OS/360 MFT (Multitasking with a Fixed number of Tasks) provided multitasking: several memory partitions, each of a fixed size, were set up when the operating system was installed and when the operator redefined them. For example, there could be a small partition, two medium partitions, and 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 MVT (Multitasking with a Variable number of Tasks) was an enhancement that further refined memory use. Instead of using fixed-size memory partitions, MVT allocated memory to regions for job steps as needed, provided enough contiguous physical memory was available. This was a significant advance over MFT's memory management, but had some weaknesses: if a job allocated memory dynamically (as most sort
Sorting algorithm
In computer science, a sorting algorithm is an algorithm that puts elements of a list in a certain order. The most-used orders are numerical order and lexicographical order...
programs and database management system
Database management system
A database management system is a software package with computer programs that control the creation, maintenance, and use of a database. It allows organizations to conveniently develop databases for various applications by database administrators and other specialists. A database is an integrated...
s do), the programmers had to estimate the job's maximum memory requirement and pre-define it for MVT. A job step that contained a mix of small and large programs wasted memory while the small programs ran. Most seriously, memory could become fragmented
Fragmentation (computer)
In computer storage, fragmentation is a phenomenon in which storage space is used inefficiently, reducing storage capacity and in most cases reducing the performance. The term is also used to denote the wasted space itself....
, i.e., 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 some current jobs finished before starting any new ones.
In the early 1970s IBM sought to mitigate these difficulties by introducing virtual memory
Virtual memory
In computing, virtual memory is a memory management technique developed for multitasking kernels. This technique virtualizes a computer architecture's various forms of computer data storage , allowing a program to be designed as though there is only one kind of memory, "virtual" memory, which...
(which IBM called "virtual storage"), which allowed programs to request address space
Address space
In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity.- Overview :...
s larger than physical memory. The original implementations had a single virtual address space, shared by all jobs. OS/VS1 was 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 were less severe because jobs could request much larger address spaces and the requests came out of a 16 MiB pool even if physical storage was smaller.
In the mid-1970s IBM introduced MVS, which not only supported virtual storage that was larger than the available real storage,Some processors could take more physical storage than the size of a single address space, but still much smaller than the aggregate size of a typical workload's virtual 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 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
Multiprocessing
Multiprocessing is the use of two or more central processing units within a single computer system. The term also refers to the ability of a system to support more than one processor and/or the ability to allocate tasks between them...
capabilities. Like its MVT and OS/VS2 SVS
OS/VS2 (SVS)
Single Virtual Storage refers to Release 1 of Operating System/Virtual Storage 2 ; it is the successor system to the MVTBut not 65MP option of Operating System/360...
predecessors, MVS supported multiprogramming
Multiprogramming
Computer multiprogramming is the allocation of a computer system and its resources to more than one concurrent application, job or user ....
; program instructions and associated data are scheduled by 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, the computer is able to switch back and forth between active and inactive programs.
Early editions of MVS (mid-1970s) were among the first of the IBM OS series to support multiprocessor
Multiprocessor
Computer system having two or more processing units each sharing main memory and peripherals, in order to simultaneously process programs.Sometimes the term Multiprocessor is confused with the term Multiprocessing....
configurations, though the M65MP variant of OS/360 running on 360 Models 65 and 67
IBM System/360 Model 67
The IBM System/360 Model 67 was an important IBM mainframe model in the late 1960s. Unlike the rest of the S/360 series, it included features to facilitate time-sharing applications, notably a DAT box to support virtual memory and 32-bit addressing...
had provided limited multiprocessor support. The 360 Model 67 had also hosted the multiprocessor capable TSS/360
TSS/360
The IBM Time Sharing System TSS/360 was an early time-sharing operating system designed exclusively for a special model of the System/360 line of mainframes, the Model 67. Made available on a trial basis to a limited set of customers in 1967, it was never officially released as a supported product...
, MTS
Michigan Terminal System
The Michigan Terminal System is one of the first time-sharing computer operating systems. Initially developed in 1967 at the University of Michigan for use on IBM S/360-67, S/370 and compatible mainframe computers, it was developed and used by a consortium of eight universities in the United...
and CP-67
CP-67
CP-67 was the control program portion of CP/CMS, a virtual machine operating system developed for the IBM System/360-67 by IBM's Cambridge Scientific Center. It was a reimplementation of their earlier research system CP-40, which ran on a one-off customized S/360-40...
operating systems. Because multiprocessing systems can execute instructions simultaneously, they offer greater processing power than single-processing system. As 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
Tightly Coupled Systems
Tightly Coupled Systems are systems in which CPUs are connected together in such a way that they share some or all of the system’s memory and I/O resources. They are also called multiprocessor systems.- References :...
, which means that the computers share the same real storage and are controlled by a single copy of the operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
. MVS retained both the loosely coupled multiprocessing
Multiprocessing
Multiprocessing is the use of two or more central processing units within a single computer system. The term also refers to the ability of a system to support more than one processor and/or the ability to allocate tasks between them...
of Attached Support Processor(ASP)Via Job Entry Subsystem 3 (JES3) and 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 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
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
together two or more data processing systems via shared disks and Channel-to-Channedl 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 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
CICS
Customer Information Control System is a transaction server that runs primarily on IBM mainframe systems under z/OS and z/VSE.CICS is a transaction manager designed for rapid, high-volume online processing. This processing is mostly interactive , but background transactions are possible...
, which ran in a single address space—and the DB2
IBM DB2
The IBM DB2 Enterprise Server Edition is a relational model database server developed by IBM. It primarily runs on Unix , Linux, IBM i , z/OS and Windows servers. DB2 also powers the different IBM InfoSphere Warehouse editions...
relational database management system
Relational database management system
A relational database management system is a database management system that is based on the relational model as introduced by E. F. Codd. Most popular databases currently in use are based on the relational database model....
needed more than 8 MB of application address space to run efficiently. (Early versions were configured into two address spaces that communicated via 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
Job Control Language
Job Control Language is a scripting language used on IBM mainframe operating systems to instruct the system on how to run a batch job or start a subsystem....
(JCL), which was originally designed for batch processing
Batch processing
Batch processing is execution of a series of programs on a computer without manual intervention.Batch jobs are set up so they can be run to completion without manual intervention, so all input data is preselected through scripts or command-line parameters...
but from the 1970s onwards was also used to start and allocate resources to long-running interactive jobs such CICS
CICS
Customer Information Control System is a transaction server that runs primarily on IBM mainframe systems under z/OS and z/VSE.CICS is a transaction manager designed for rapid, high-volume online processing. This processing is mostly interactive , but background transactions are possible...
; and TSO
Time Sharing Option
In computing, Time Sharing Option is an interactive time-sharing environment for IBM mainframe operating systems, including OS/360 MVT, OS/VS2 , MVS, OS/390, and z/OS.- Overview :TSO fulfills a similar purpose to Unix login sessions...
(Time Sharing Option), the interactive time-sharing
Time-sharing
Time-sharing is the sharing of a computing resource among many users by means of multiprogramming and multi-tasking. Its introduction in the 1960s, and emergence as the prominent model of computing in the 1970s, represents a major technological shift in the history of computing.By allowing a large...
interface, which was mainly used to run development tools and a few end-user information systems. ISPF
ISPF
In computing, Interactive System Productivity Facility is a software product for the z/OS operating system that runs on IBM mainframes...
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 is command line, although facilities 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 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, but 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 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 were invoked in case the system detected an error (actually, hardware processor or storage error, or software error). Each recovery routine made the 'mainline' function reinvokable, captured error diagnostic data sufficient to debug 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 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 the fact that processing progresses despite an error can overwrite the tracks. Early date 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 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 introduced an on-demand hypervisor
Hypervisor
In computing, a hypervisor, also called virtual machine manager , is one of many hardware virtualization techniques that allow multiple operating systems, termed guests, to run concurrently on a host computer. It is so named because it is conceptually one level higher than a supervisory program...
, a major serviceability tool, called Dynamic Support System (DSS), in the first release of MVS. This facility could be invoked to initiate 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 was used. Due to the overhead of this tool, it was removed from customer-available MVS systems. Program-Event Recording (PER) exploitation 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 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
A logical partition, commonly called an LPAR, is a subset of computer's hardware resources, virtualized as a separate computer. In effect, a physical machine can be partitioned into multiple logical partitions, each hosting a separate operating system....
(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
IBM Parallel Sysplex
In computing, a Parallel Sysplex is a cluster of IBM mainframes acting together as a single system image with z/OS. Used for disaster recovery, Parallel Sysplex combines data sharing and parallel computing to allow a cluster of up to 32 systems to share a workload for high performance and high...
, introduced in September, 1990. Instances interoperate through a software component called a Cross-system Coupling Facility
IBM XCF
In IBM mainframes, a Cross-system coupling facility, or XCF, is a component of z/OS that manages communications between applications in a sysplex...
(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
Systems Network Architecture
Systems Network Architecture is IBM's proprietary networking architecture created in 1974. It is a complete protocol stack for interconnecting computers and their resources. SNA describes the protocol and is, in itself, not actually a program...
(SNA) or, more recently, via TCP/IP. The z/OS operating system (MVS' most recent descendant) also has native support to execute POSIX
POSIX
POSIX , an acronym for "Portable Operating System Interface", is a family of standards specified by the IEEE for maintaining compatibility between operating systems...
applications.
Files are properly called data set
Data set (IBM mainframe)
data set , dataset , is a computer file having a record organization. The term pertains to the IBM mainframe operating system line, starting with OS/360, and is still used by its successors, including the current z/OS. Those systems historically preferred this term over a file...
s in MVS. Names of those files are organized in catalogs that are VSAM files themselves.
The native encoding scheme of MVS and its peripherals is Big Endian EBCDIC
EBCDIC
Extended Binary Coded Decimal Interchange Code is an 8-bit character encoding used mainly on IBM mainframe and IBM midrange computer operating systems....
, but over time IBM added hardware-accelerated services to perform translation and support of ASCII
ASCII
The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...
, Little Endian, and Unicode
Unicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...
.
MVS filesystem
Data set names (DSNs, mainframe term for filenames) are organized in 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 were utility programs that performed similar functions to those of Windows ExplorerWindows Explorer
This article is about the Windows file system browser. For the similarly named web browser, see Internet ExplorerWindows Explorer is a file manager application that is included with releases of the Microsoft Windows operating system from Windows 95 onwards. It provides a graphical user interface...
(but without the GUI
Gui
Gui or guee is a generic term to refer to grilled dishes in Korean cuisine. These most commonly have meat or fish as their primary ingredient, but may in some cases also comprise grilled vegetables or other vegetarian ingredients. The term derives from the verb, "gupda" in Korean, which literally...
and usually in batch processing
Batch processing
Batch processing is execution of a series of programs on a computer without manual intervention.Batch jobs are set up so they can be run to completion without manual intervention, so all input data is preselected through scripts or command-line parameters...
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 actual directories but just a naming convention (like the original Macintosh File System
Macintosh File System
Macintosh File System is a volume format created by Apple Computer for storing files on 400K floppy disks. MFS was introduced with the Macintosh 128K in January 1984....
, where folder hierarchy was an illusion maintained by the Finder). TSO
Time Sharing Option
In computing, Time Sharing Option is an interactive time-sharing environment for IBM mainframe operating systems, including OS/360 MVT, OS/VS2 , MVS, OS/390, and z/OS.- Overview :TSO fulfills a similar purpose to Unix login sessions...
supports a default prefix for files (similar to 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 were record-oriented
Record-oriented filesystem
In computer science, a record-oriented filesystem is a file system where files are stored as collections of records. There are several different record formats; the details vary depending on the particular system...
. MVS inherited three main types from its predecessors:
- Sequential data sets were normally read one record at a time from beginning to end.
- In BDAMBasic direct access methodIn IBM mainframe operating systems, basic direct access method is an access method to read and write data sets directly. In BDAM, the programmer has complete control of the organization of the file...
(direct access) data sets, the application program had to specify the physical location of the data it wanted to access (usually by specifying the offset from the start of the data set). - In ISAMISAMISAM stands for Indexed Sequential Access Method, a method for indexing data for fast retrieval. ISAM was originally developed by IBM for mainframe computers...
data sets a specified section of each record was defined as a key that could be used as a key to look up specific records. The key quite often consisted of multiple fieldsField (computer science)In computer science, data that has several parts can be divided into fields. Relational databases arrange data as sets of database records, also called rows. Each record consists of several fields; the fields of all records form the columns....
but these had to be contiguous and in the right order; and key values had to be unique. Hence an IBM ISAM file could have only one key, equivalent to the primary key of a relational databaseRelational databaseA relational database is a database that conforms to relational model theory. The software used in a relational database is called a relational database management system . Colloquial use of the term "relational database" may refer to the RDBMS software, or the relational database itself...
table; ISAM could not support foreign keyForeign keyIn the context of relational databases, a foreign key is a referential constraint between two tables.A foreign key is a field in a relational table that matches a candidate key of another table...
s.
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 the VTOC
VTOC
In the IBM mainframe storage architecture, Volume Table Of Contents, or VTOC, is a data structure, that provides a way of locating the data sets that reside on a particular disk volume. It can reside within the first 64K tracks on the volume, and lists the names of each data set on the volume as...
disk structure.
Early IBM database management system
Database management system
A database management system is a software package with computer programs that control the creation, maintenance, and use of a database. It allows organizations to conveniently develop databases for various applications by database administrators and other specialists. A database is an integrated...
s 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
Virtual memory
In computing, virtual memory is a memory management technique developed for multitasking kernels. This technique virtualizes a computer architecture's various forms of computer data storage , allowing a program to be designed as though there is only one kind of memory, "virtual" memory, which...
operating systems introduced a new file management component, VSAM, which provided similar facilities:
- Entry-Sequenced Datasets (ESDS) provided facilities similar to those of both sequential and BDAM datasets, since they could be read either from start to finish or directly by specifying an offset from the start.
- Key-Sequenced Datasets (KSDS) were a major upgrade from ISAM: they allowed secondary keys with non-unique values and keys formed by concatenating non-contiguous fields in any order; they greatly reduced the performance problems caused by overflow records in ISAM; and they greatly reduced the risk that a software or hardware failure in the middle of an index update might corrupt the index.
These VSAM formats became the basis of IBM's database management systems, IMS/VS and DB2
IBM DB2
The IBM DB2 Enterprise Server Edition is a relational model database server developed by IBM. It primarily runs on Unix , Linux, IBM i , z/OS and Windows servers. DB2 also powers the different IBM InfoSphere Warehouse editions...
- usually ESDS for the actual data storage and KSDS for indexes.
VSAM also included a catalog component used for MVS' master catalog.
Partitioned datasets (PDS) were sequential datasets subdivided into "members" that could be processed as sequential files in their own right. The most important use of PDS was for program libraries - system administrators used the main PDS as a way to allocate disk space to a project and the project team then created and edited the members.
Generation Data Groups (GDGs) 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 a lot more than 3 generations and some applications used GDGs to collect data from several sources and feed 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
Job Control Language
Job Control Language is a scripting language used on IBM mainframe operating systems to instruct the system on how to run a batch job or start a subsystem....
).
Modern versions of MVS (e.g., z/OS) also support POSIX-compatible "slash" filesystems along with facilities for integrating the two filesystems. That is, the OS can make an MVS dataset appear as a file to a POSIX program or subsystem. These newer filesystems include Hierarchical File System (HFS) (not to be confused with Apple's Hierarchical File System
Hierarchical File System
Hierarchical File System is a file system developed by Apple Inc. for use in computer systems running Mac OS. Originally designed for use on floppy and hard disks, it can also be found on read-only media such as CD-ROMs...
) and zFS
ZFS (IBM file system)
zFS refers to two different IBM file systems:* zFS most often refers to z/OS Distributed File Service zSeries File System, the newest POSIX-style hierarchical file system for IBM's z/OS operating system, a successor to that operating system's HFS...
(not to be confused with Sun's ZFS
ZFS
In computing, ZFS is a combined file system and logical volume manager designed by Sun Microsystems. The features of ZFS include data integrity verification against data corruption modes , support for high storage capacities, integration of the concepts of filesystem and volume management,...
).
History and modernity
MVS is now a part of 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 64-bit applications.MVS releases up to 3.8j (24-bit, released in 1981) were freely available and it is now possible to run the MVS 3.8j release in mainframe emulators for free.
MVS/370
MVS/370 is a generic term for all versions of MVS operating systemOperating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
prior to MVS/XA.OS/VS2 Release 2 through 3.8, MVS/SE and MVS/SP Version 1 The System/370
System/370
The IBM System/370 was a model range of IBM mainframes announced on June 30, 1970 as the successors to the System/360 family. The series maintained backward compatibility with the S/360, allowing an easy migration path for customers; this, plus improved performance, were the dominant themes of the...
architecture, at the time MVS was released, supported only 24-bit virtual addresses, so the MVS/370 operating system architecture
Architecture
Architecture is both the process and product of planning, designing and construction. Architectural works, in the material form of buildings, are often perceived as cultural and political symbols and as works of art...
is based on a 24-bit address. Because of this 24-bit address length, programs running under MVS/370 are each given 16 megabytes of contiguous virtual storage.
MVS/XA
MVS/XA, or Multiple Virtual Storage/Extended Architecture, was a version of MVS that supported the 370-XA architecture, which expanded addresses from 24 bits to 31 bits, providing a 2 gigabyteGigabyte
The gigabyte is a multiple of the unit byte for digital information storage. The prefix giga means 109 in the International System of Units , therefore 1 gigabyte is...
addressable memory area. It also supported a 24-bit legacy addressing mode for older 24-bit applications (i.e. those that stored a 24-bit address in the lower 24 bits of a 32-bit word and utilized the upper 8 bits of that word for other purposes).
MVS/ESA
MVS/ESA: MVS Enterprise System Architecture. Version of MVS, first introduced as MVS/SP Version 3 in February 1988. Replaced by/renamed as OS/390 late 1995 and subsequently as z/OSZ/OS
z/OS is a 64-bit operating system for mainframe computers, produced by IBM. It derives from and is the successor to OS/390, which in turn followed a string of MVS versions.Starting with earliest:*OS/VS2 Release 2 through Release 3.8...
.
MVS/ESA OpenEdition: upgrade to Version 4 Release 3 of MVS/ESA announced February 1993 with support for POSIX
POSIX
POSIX , an acronym for "Portable Operating System Interface", is a family of standards specified by the IEEE for maintaining compatibility between operating systems...
and other standards. While the initial release only had National Institute of Standards and Technology
National Institute of Standards and Technology
The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...
(NIST) certification for Federal Information Processing Standard
Federal Information Processing Standard
A Federal Information Processing Standard is a publicly announced standardization developed by the United States federal government for use in computer systems by all non-military government agencies and by government contractors, when properly invoked and tailored on a contract...
(FIPS) 151 compliance, subsequent releases were certified at higher levels and by other organizations, e.g. X/Open and its successor, The Open Group. It included about 1 million new lines of code, which provide an API shell, utilities, and an extended user interface. Works with a hierarchical file system provided by DFSMS (Data Facility System Managed Storage). The shell and utilities are based on Mortice Kerns' InterOpen products. Independent specialists reckon it was over 80% open systems-compliant—more than most Unix systems. DCE2 support announced February 1994, and many application development tools in March 1995. Mid 1995 IBM started to stop referring to OpenEdition as a separate entity, as all the open features became a standard part of vanilla MVS/ESA SP Version 5 Release 1. Under OS/390
OS/390
OS/390 is an IBM operating system for the System/390 IBM mainframe computers.OS/390 was introduced in late 1995 in an effort, led by the late Randy Stelman, to simplify the packaging and ordering for the key, entitled elements needed to complete a fully functional MVS operating system package...
, it became Unix System Services, and has kept that name under z/OS
Z/OS
z/OS is a 64-bit operating system for mainframe computers, produced by IBM. It derives from and is the successor to OS/390, which in turn followed a string of MVS versions.Starting with earliest:*OS/VS2 Release 2 through Release 3.8...
.
Closely related operating systems
Japanese mainframe manufacturers FujitsuFujitsu
is a Japanese multinational information technology equipment and services company headquartered in Tokyo, Japan. It is the world's third-largest IT services provider measured by revenues....
and Hitachi
Hitachi
Hitachi is a multinational corporation specializing in high-technology.Hitachi may also refer to:*Hitachi, Ibaraki, Japan*Hitachi province, former province of Japan*Prince Hitachi and Princess Hitachi, members of the Japanese imperial family...
both repeatedly and illegally obtained IBM's MVS source code
Source code
In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...
and internal documentation in one of the 20th century's most famous cases of industrial espionage
Industrial espionage
Industrial espionage, economic espionage or corporate espionage is a form of espionage conducted for commercial purposes instead of purely national security purposes...
. Fujitsu relied heavily on IBM's code in its MSP mainframe operating system, and likewise Hitachi did the same for its VOS3 operating system. MSP and VOS3 were heavily marketed in Japan, where they still hold a substantial share of the mainframe installed base, but also to some degree in other countries, notably Australia. Even IBM's bugs and documentation misspellings were faithfully copied. IBM cooperated with the U.S. Federal Bureau of Investigation
Federal Bureau of Investigation
The Federal Bureau of Investigation is an agency of the United States Department of Justice that serves as both a federal criminal investigative body and an internal intelligence agency . The FBI has investigative jurisdiction over violations of more than 200 categories of federal crime...
in a sting operation
Sting operation
In law enforcement, a sting operation is a deceptive operation designed to catch a person committing a crime. A typical sting will have a law-enforcement officer or cooperative member of the public play a role as criminal partner or potential victim and go along with a suspect's actions to gather...
, reluctantly supplying Fujitsu and Hitachi with proprietary MVS and mainframe hardware technologies during the course of multi-year investigations culminating in the early 1980s -- investigations which implicated senior company managers and even some Japanese government officials. (Amdahl
Amdahl Corporation
Amdahl Corporation is an information technology company which specializes in IBM mainframe-compatible computer products. Founded in 1970 by Dr. Gene Amdahl, a former IBM employee, it has been a wholly owned subsidiary of Fujitsu since 1997...
was not involved in Fujitsu's theft of IBM's IP; indeed, any communications from Amdahl to Fujitsu were through "Amdahl Only Specifications" which were scrupulously cleansed of any IBM IP or any references to IBM's IP.) Subsequent to the investigations, IBM reached multi-million dollar settlements with both Fujitsu and Hitachi, collecting substantial fractions of both companies' profits for many years (reliable reports are that the settlements exceeded US$500,000,000 ... exceeded half a billion dollars). (The three companies have long since amicably agreed to many joint business ventures. For example, in 2002 IBM and Hitachi collaborated on developing the IBM z800 mainframe model.) Because of this incident, MSP and VOS3 are properly classified as "forks"
Fork (software development)
In software engineering, a project fork happens when developers take a legal copy of source code from one software package and start independent development on it, creating a distinct piece of software...
of MVS, and many third party software vendors with MVS-compatible products were able to produce MSP- and VOS3-compatible versions with little or no modification.
When IBM introduced its 64-bit
64-bit
64-bit is a word size that defines certain classes of computer architecture, buses, memory and CPUs, and by extension the software that runs on them. 64-bit CPUs have existed in supercomputers since the 1970s and in RISC-based workstations and servers since the early 1990s...
z/Architecture
Z/Architecture
z/Architecture, initially and briefly called ESA Modal Extensions , refers to IBM's 64-bit computing architecture for IBM mainframe computers. IBM introduced its first z/Architecture-based system, the zSeries Model 900, in late 2000. Later z/Architecture systems include the IBM z800, z990, z890,...
mainframes in the year 2000, IBM also introduced the 64-bit z/OS operating system, the direct successor to OS/390 and MVS. Fujitsu and Hitachi opted not to license IBM's z/Architecture for their quasi-MVS operating systems and hardware systems, and so MSP and VOS3, while still nominally supported by their vendors, maintain most of MVS's 1980s architectural limitations to the present day. Since z/OS still supports MVS-era applications and technologies -- indeed, z/OS still contains most of MVS's code, albeit greatly enhanced and improved over decades of evolution -- applications (and operational procedures) running on MSP and VOS3 can move to z/OS much more easily than to other operating systems.
See also
- HerculesHercules emulatorHercules is a computer emulator which allows software designed for IBM mainframe computers and for plug-compatible mainframes to run on other types of computer hardware: notably on low-cost personal computers...
a S/370, S/390, and zSeries emulator capable of running MVS - Utility programsIBM mainframe utility programsIBM mainframe utility programs are supplied with IBM mainframe operating systems such as MVS to carry out various tasks associated with datasets, etc.-History/Common JCL:...
supplied with MVS (and successor) operating systems - BatchPipesBatchPipesIn IBM mainframes, BatchPipes is a batch job processing utility designed for the MVS/ESA operating system, and all later incarnations—OS/390 and z/OS.-Core function:...
is a batch job processingBatch processingBatch processing is execution of a series of programs on a computer without manual intervention.Batch jobs are set up so they can be run to completion without manual intervention, so all input data is preselected through scripts or command-line parameters...
utility designed for the MVS/ESA operating system, and all later incarnations—OS/390OS/390OS/390 is an IBM operating system for the System/390 IBM mainframe computers.OS/390 was introduced in late 1995 in an effort, led by the late Randy Stelman, to simplify the packaging and ordering for the key, entitled elements needed to complete a fully functional MVS operating system package...
and z/OSZ/OSz/OS is a 64-bit operating system for mainframe computers, produced by IBM. It derives from and is the successor to OS/390, which in turn followed a string of MVS versions.Starting with earliest:*OS/VS2 Release 2 through Release 3.8...
.
External links
- IBM: z/OS V1R11.0 MVS Manuals
- IBM: z/OS V1R8.0 MVS manuals-Broken link
- MVS: the operating system that keeps the world going
- MVS... a long history
- Functional structure of IBM virtual storage operating systems Part II: OS/VS2-2 concepts and philosophies by A. L. Scherr
- Online demo of MVS 3.8J as run with the Hercules emulator