Multiple Virtual Storage, more commonly called MVS, was the most commonly used operating system on the System/370 and System/390 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.
The IBM System/360 (S/360) is a family of mainframe computer systems that was announced by IBM on April 7, 1964, and delivered between 1965 and 1978. It was the first family of computers designed to cover the complete range of applications, from small to large, both commercial and scientific. The design made a clear distinction between architecture and implementation, allowing IBM to release a suite of compatible designs at different prices. All but the only partially compatible Model 44 and the most expensive systems use microcode to implement the instruction set, which features 8-bit byte addressing and binary, decimal and hexadecimal floating-point calculations.
In computing, virtual memory, or virtual storage is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" which "creates the illusion to users of a very large (main) memory".
A direct-access storage device (DASD) is a secondary storage device in which "each physical record has a discrete location and a unique address". IBM coined the term DASD as a shorthand describing hard disk drives, magnetic drums, and data cells. Later, optical disc drives and flash memory units are also classified as DASD. The term DASD contrasts with sequential storage media such as magnetic tape, and unit record equipment such as card devices like card readers and punches.
The IBM System/370 (S/370) is a model range of IBM mainframe computers announced on June 30, 1970 as the successors to the System/360 family. The series mostly maintains backward compatibility with the S/360, allowing an easy migration path for customers; this, plus improved performance, were the dominant themes of the product announcement. In September 1990, the System/370 line was replaced with the System/390.
VM is 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.
z/Architecture, initially and briefly called ESA Modal Extensions (ESAME), is IBM's 64-bit CISC instruction set architecture implemented by its mainframe computers. IBM introduced its first z/Architecture-based system, the z900, in late 2000. Later z/Architecture systems include the IBM z800, z990, z890, System z9, System z10, zEnterprise 196, zEnterprise 114, zEC12, zBC12, z13, z14 and z15.
In computing, channel I/O is a high-performance input/output (I/O) architecture that is implemented in various forms on a number of computer architectures, especially on mainframe computers. In the past, channels were generally implemented with custom devices, variously named channel, I/O processor, I/O controller, I/O synchronizer, or DMA controller.
Count key data (CKD) is a direct-access storage device (DASD) data recording format introduced in 1964, by IBM with its IBM System/360 and still being emulated on IBM mainframes. It is a self-defining format with each data record represented by a Count Area that identifies the record and provides the number of bytes in an optional Key Area and an optional Data Area. This is in contrast to devices using fixed sector size or a separate format track.
In IBM mainframe operating systems from the OS/360 and successors line, a Unit Control Block (UCB) is a memory structure, or a control block, that describes any single input/output peripheral device (unit), or an exposure (alias), to the operating system. Certain data within the UCB also instructs the Input/Output Supervisor (IOS) to use certain closed subroutines in addition to normal IOS processing for additional physical device control.
An access method is a function of a mainframe operating system that enables access to data on disk, tape or other external devices. Access methods were present in several mainframe operating systems since the late 1950s, under a variety of names; the name access method was introduced in 1963 in the IBM OS/360 operating system. Access methods provide an application programming interface (API) for programmers to transfer data to or from device, and could be compared to device drivers in non-mainframe operating systems, but typically provide a greater level of functionality.
A Supervisor Call instruction (SVC) is a hardware instruction in the System/360 family of IBM mainframe computers up to contemporary zSeries used to cause an interrupt to request a service from the operating system. The system routine providing the service is called an SVC routine. SVC is a specific implementation of a system call.
In IBM mainframe operating systems, Execute Channel Program (EXCP) is a macro generating a system call, implemented as a Supervisor Call instruction, for low-level device access, where the programmer is responsible for providing a channel program—a list of device-specific commands (CCWs)—to be executed by I/O channels, control units and devices. EXCP for OS/360 and successors is more specifically described in the OS System Programmer's Guide.; EXCP for DOS/360 and successors is more specifically described in DOS Supervisor and I/O Macros. This article mostly reflects OS/360 through z/OS; some details are different for TOS/360 and DOS/360 through z/VSE.
OS/360, officially known as IBM System/360 Operating System, is a discontinued batch processing operating system developed by IBM for their then-new System/360 mainframe computer, announced in 1964; it was influenced by the earlier IBSYS/IBJOB and Input/Output Control System (IOCS) packages for the IBM 7090/7094 and even more so by the PR155 Operating System for the IBM 1410/7010 processors. It was one of the earliest operating systems to require the computer hardware to include at least one direct access storage device.
Single Virtual Storage (SVS) refers to Release 1 of Operating System/Virtual Storage 2 (OS/VS2); it is the successor system to the MVT option of Operating System/360. OS/VS2 (SVS) was a stopgap measure pending the availability of MVS, although IBM provided support and enhancements to SVS long after shipping MVS.
The IBM System/360 architecture is the model independent architecture for the entire S/360 line of mainframe computers, including but not limited to the instruction set architecture. The elements of the architecture are documented in the IBM System/360 Principles of Operation and the IBM System/360 I/O Interface Channel to Control Unit Original Equipment Manufacturers' Information manuals.
In IBM mainframe operating systems, Execute Direct Access Program (XDAP) is a pseudo access method for accessing direct access datasets on a block by block basis. XDAP is more specifically described in the OS System Programmer's Guide.
The IBM Administrative Terminal System, also known as ATS/360, provided text- and data-management tools for working with documents to users of IBM System/360 systems.
In MVS/370 and successor versions of IBM mainframe operating systems, Start Input/Output (STARTIO) is a macro instruction and a "branch entry" for low-level device access, where the programmer is responsible for providing a list of device-specific CCWs, that is, a channel program, to be executed by I/O channels, control units and devices and a number of "exits", several of which may be immediate returns to the Input/Output Supervisor (IOS). Invokers of STARTIO must be in supervisor mode and key 0. STARTIO interfaces directly with the IOS component of MVS.
The Input/Output Supervisor (IOS) is that portion of the control program in the IBM mainframe OS/360 and successors operating systems 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 operations.
