Wikipedia of IBM Mainframe Computers

Mainframe Definitions:
Mainframe Definitions

Mainframe is a High performance Multi User computer system which is the most scalable, available, reliable and secure machine in the world capable of handling numerous terminals and peripherals simultaneously.


What is Terminal

A device, usually equipped with a keyboard and display device (without a CPU), capable of sending and receiving information over a network. IBM 3270 terminals are used to connect to a mainframe computer.


What is Emulator

Emulator is a computer program that duplicates the functions of an IBM 3270 mainframe terminal which was used to connect to a mainframe computer. IBM no longer manufactures 3270 terminals, instead we use a PC running a software that mimics the IBM terminal. This software is called as Terminal Emulator.

What is a Mainframe Channel

A mainframe channel connect to one or more controllers via either pairs of large "bus and tag" cables or, fiber optic ESCON (Enterprise System CONnection) cables and FICON (Fibre Connection), which has the ability controlling one or more devices. This is one of the important term in mainframe technology since it has the ability of take care of huge input and output functions.


Batch processing

Batch applications are processed on the mainframe without user interaction. A batch job is submitted on the computer; the job reads and processes data in bulk— perhaps terabytes of data— and produces output, such as customer billing statements.

Online processing

Transaction processing that occurs interactively with the end user is referred to as online transaction processing or OLTP.

Examples include:

  • ATM machine transactions such as deposits, withdrawals, inquiries, and transfers

  • Supermarket payments with debit or credit cards

  • Airline Ticket booking over the Internet




    Abnormal end. End of a task or job because of an error condition that cannot be resolved by system recovery facilities while the task is performed.



    Application programming interface. A software interface that enables applications to communicate with each other. An API is the set of programming language constructs or statements that can be coded in an application program to obtain the specific functions and services provided by an underlying operating system or service program.



    A computer program that converts assembler language instructions into binary machine language (object code



    A system program that processes the output of language translators and compilers into an executable program (load module or program object). It replaces the linkage editor and batch loader in the MVS operating system.



    A portion of storage used to hold input or output data temporarily


    Buffer Pool

    A group of identical buffers that can be used interchangeably. The purpose of buffer pools is to cache table and index data from disk. All databases have their own buffer pools.



    A special-purpose buffer storage, smaller and faster than main storage, used to hold a copy of instructions and data obtained from main storage and likely to be needed next by the processor.



    A directory of data sets, with reference to their locations.


    Cataloged data set

    A data set that is represented in an index or hierarchy of indexes that provide the means for locating it.


    Cataloged procedure

    A set of job control language (JCL) statements placed in a library and retrievable by name.



    A group of interconnected computers that are working together as one unit.



    Common Business-Oriented Language (COBOL). A high-level language, based on English, that is primarily used for business applications.



    A communication area made available to applications running under CICS.



    A request to make all changes to resources since the last commit or backout or, for the first unit of recovery, since the beginning of the application.



    A program that translates a source program into an machine executable program


    Compiler options

    Keywords that can be specified to control certain aspects of compilation. Compiler options can control the nature of the output generated by the compiler, the types of printed output to be produced, the efficient use of the compiler, and the destination of error messages.


    Condition code (Hardware)

    A two bit data area that many instructions set to summarize the result of executing the instruction. For example, an Add instruction may set the condition code to 00 to indicate the result of the instruction is 0, 01 to indicate the result is negative, 10 to indicate the result is greater than 0, or 11 to indicate the result represents an overflow; it is greater than the capacity of the output area.


    Condition code (Software)

    A 12-bit binary value many programs set to indicate the result of running the program. This code is often referred to as a return code.



    An input/output device on a computer, reserved for communication between the computer operator or maintenance engineer and the computer.


    Control interval

    A fixed-length area or disk in which VSAM stores records and creates distributed free space. Also, in a key-sequenced data set or file, the set of records that an entry in the sequence-set index record points to. The control interval is the unit of information that VSAM transmits to or from disk. A control interval always includes an integral number of physical records.


    Control Unit

    A device that coordinates and controls the operation of one or more input/output devices, and synchronizes the operation of such devices with the operation of the system as a whole.



    Customer Information Control System, An online transaction processing (OLTP) system that provides specialized interfaces to databases, files and terminals in support of business and commercial applications. CICS enables transactions entered at remote terminals to be processed concurrently by user-written application programs.



    On a magnetic disk or in an assembly of disks, the set of all tracks that can be accessed by all the magnetic heads of a comb in a given position, without repositioning the access mechanism.



    An IBM licensed program that is a high-speed data-processing utility. DFSORT provides an efficient and flexible way to handle sorting, merging, and copying operations, as well as providing versatile data manipulation at the record, field, and bit level.



    A DFSMS/MVS functional component that provides functions for storage management, data management, program management, device management, and distributed data access.



    A DFSMS/MVS functional component used to copy, move, dump, and restore data sets and volumes.



    A DFSMS/MVS functional component used for backing up and recovering data, and managing space on volumes in the storage hierarchy.



    A DFSMS/MVS functional component that manages removable media.



     DASD stands for Direct Access Storage Device. This indicates to any type of storage that was directly (randomly) addressable independent of the location of the data.


    Data set

    A named collection of related data records that is stored on disk or tapes. Almost equivalent to a file in Windows operating system. But a data set differs from a 'file', in that it has a defined format, as opposed to a file that is just a collection of data with no defined format in Windows.



    Database management system, A software system that controls the creation, organization, and modification of a database and the access to the data that is stored in it.



    IBM relational database management system.



    An error condition in which processing cannot continue because each of two elements of the process is waiting for an action by or a response from the other.



    The process of writing two sets of identical records in order to create a second copy of data.



    Generation data group, A collection of historically related non-VSAM data sets that are arranged in chronological order; each data set is called a generation data set.



    In a network, a point at which circuits are either connected or switched.



    An IBM program used to process access method services commands. It can be invoked as a job or jobstep, from a TSO terminal, or from within a user's application program.



    Information Management System, Any of several system environments available with a database manager and transaction processing that are capable of managing complex databases and terminal networks.



    Interactive System Productivity Facility, A dialog manager for interactive applications. It provides control and services to permit execution of dialogs.



    A suspension of a process, such as the execution of a computer program, caused by an event external to that process, and performed in such a way that the process can be resumed.



    Job control language, A sequence of commands used to identify a job to an operating system and to describe a job's requirements.



    Job entry subsystem, A system facility for spooling, job queuing, and managing I/O.



    A unit of work for an operating system. Jobs are defined by JCL statements.


    Load module

    An executable program stored in a partitioned data set program library.


    Logical partition (LPAR)

    A subset of a single system that contains resources (processors, memory, and input/output devices). A logical partition operates as an independent system. If hardware requirements are met, multiple logical partitions can exist within a system. Normally this feature is implemented in all the mainframe systems. By this feature it is possible to create partitions and by which CPUs and I/O sub-systems can be shared between logical partitions.



    The simultaneous execution of two or more computer programs or sequences of instructions.



    Mode of operation that provides for the concurrent, or interleaved, execution of two or more tasks, or threads.


    Nonvolatile storage

    Additional random access electronic storage with a backup battery power source, available with an IBM Cache Storage Control, used to retain data during a power outage. Nonvolatile storage, accessible from all storage directors, stores data during DASD fast write and dual copy operations.


    Parallel processing

    The simultaneous processing of units of work by many servers. The units of work can be either transactions or subdivisions of large units of work (batch).



    Partitioned data set, A data set in direct access storage that is divided into partitions, called members, each of which can contain a program, part of a program, or data.



    Partitioned data set/Extended, A system-managed data set that contains an indexed directory and members that are similar to the directory and members of partitioned data sets. A PDSE can be used instead of a partitioned data set.



    A general purpose scientific/business high-level language. PL/I is a powerful procedure-oriented language especially well suited for solving complex scientific problems or running lengthy and complicated business transactions and record-keeping applications.



    Resource Access Control Facility, An IBM security manager product that provides for access control by identifying and verifying the users to the system, authorizing access to protected resources, logging the detected unauthorized attempts to enter the system and logging the detected accesses to protected resources.



    Restructured extended executor, A general-purpose, procedural language for end-user personal programming, designed for ease by both casual general users and computer professionals. It is also useful for application macros. REXX includes the capability of issuing commands to the underlying operating system from these macros and procedures.



    The attribute of a routine or application that allows more than one user to share a single copy of a load module.


    Return code

    A code produced by a routine to indicate its success or failure. It may be used to influence the execution of succeeding instructions or programs.



    Sequential data set, A data set in which the contents are arranged in successive physical order and are stored as an entity. The data set can contain data, text, a program, or part of a program. Contrast with partitioned data set (PDS).



    System Display and Search Facility, A panel-based product that provides detailed information about jobs and job output, devices and other resources in a z/OS system.



    System management facilities. A z/OS component that provides the means for gathering and recording information for evaluating system usage.



    System management Subsystem. A DFSMS/MVS facility used to automate and centralize the management of storage. Using SMS, a storage administrator describes data allocation characteristics, performance and availability goals, backup and retention requirements, and storage requirements to the system through data class, storage class, management class, storage group, and ACS routine definitions.


    Temporary data set

    An uncataloged data set whose name begins with & or &&, that is normally used only for the duration of a job or interactive session. Contrast with permanent data set.



    A unit of work performed by one or more transaction programs, involving a specific set of input data and initiating a specific process or job.



    Time Sharing Option, The facility in z/OS that allows users to interactively share computer time and resources.


    Virtual storage

    An addressing scheme that allows external disk storage to appear as main storage.



    The storage space on DASD, tape, or optical devices, which is identified by a volume label.



    Virtual storage access method, An access method for direct or sequential processing of fixed-length and varying-length records on direct access devices. The records in a VSAM data set or file can be organized in logical sequence by a key field (key sequence), in the physical sequence in which they are written on the data set or file (entry-sequence), or by relative-record number.



    Virtual telecommunications access method, A set of programs that maintain control of the communication between terminals and application programs running under z/OS.



    Workload management, A z/OS component that prioritizes workloads and matches them with available resources.



    A widely used operating system for IBM mainframe computers that uses 64-bit central storage.

    Features of z/OS:

  • z/OS derives from and is the successor to OS/390, which in turn followed a string of MVS versions.

    z/OS supports stable mainframe programming languages such as COBOL, JCL, PL/I, ASSEMBLER, REXX, CLIST, DFSORT, SYNCSORT and subsystems like JES, TSO, RACF, VSAM, ISPF, CICS and databases like IMS, IDMS, DB2 etc.

    z/OS also supports 64-bit Java, C, C++, and UNIX APIs. z/OS can communicate directly via TCP/IP, including IPv6 and includes standard HTTP servers along with other common services such as FTP, SMTP, NFS, and CIFS/SMB.


    Next Article: List of Mainframe Software Products


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