Mainframe Glossary
202 Terms Explained
Your comprehensive reference guide to mainframe terminology, technologies, and concepts
A
ABEND
An unexpected termination of a program or job due to an error condition. Common in batch processing environments where jobs fail before completion....
Access Method
The technique used by programs to store and retrieve data from storage devices. Access methods define how data is organized, accessed, and managed on ...
ACF2
A comprehensive security software package from Broadcom (formerly CA Technologies) that provides authentication, authorization, and auditing capabilit...
ADABAS
A high-performance, inverted-list database management system from Software AG, designed for high-volume transaction processing and optimized for the N...
APF
A z/OS security mechanism that identifies programs authorized to use restricted system functions, access protected datasets, and execute privileged op...
APL
An array-oriented programming language developed by Kenneth Iverson, known for its concise mathematical notation and powerful array manipulation capab...
Application Server
Middleware software that provides a runtime environment for business applications, managing transactions, connections between user interfaces and data...
ASCII
A character encoding standard using 7 or 8 bits to represent text characters, widely used in modern computing systems including UNIX, Linux, Windows, ...
ASM
A low-level programming language that provides a one-to-one correspondence between mnemonic operation codes and machine language instructions. On main...
Addressability
A program's ability to reference all of the storage associated with its address space....
Address Space
A virtual storage area assigned to a program or task, providing isolation between different executing programs. Each address space has its own private...
Address Space Identifier
A unique numeric identifier assigned to each address space in a z/OS system, analogous to a UNIX Process ID (PID). The ASID enables the system to dist...
AES Master Key
One of the four master keys in ICSF, responsible for encrypting the Advanced Encryption Standard (AES) and Hash-based Message Authentication Code (HMA...
AMODE
The addressing mode of a program, either 24-bit (AMODE 24) or 31-bit (AMODE 31), determining the range of virtual addresses the program can access....
Asymmetric Cryptography
A method where a public and private key pair is generated; the public key is used to encrypt data, and the corresponding private key is used to decryp...
Auxiliary Storage
Secondary storage used by z/OS for paging operations, typically consisting of dedicated DASD volumes that hold pages of virtual storage when they're n...
B
Batch Processing
The execution of programs without manual intervention, typically scheduled to run during off-peak hours to process large volumes of data. Batch jobs a...
Big Iron
Colloquial term for mainframe computers, referring to their large physical size, robust construction, and reliable operation. The term emphasizes the ...
BSAM
A low-level access method for reading and writing sequential datasets that provides direct programmer control over I/O operations, buffering, and erro...
Binder
The z/OS link-editor program that processes object modules, control statements, and options to create executable load modules. The Binder combines sep...
C
CA-7
A comprehensive job scheduling and workload automation tool from Broadcom (formerly Computer Associates) that manages batch processing workflows, depe...
Catalog
A system dataset that contains metadata about the location, characteristics, and attributes of other datasets on the mainframe system. The catalog pro...
CCS
IBM's cryptographic services facility providing encryption, decryption, and key management capabilities....
CEDA
Commands used to define and manage CICS resources such as transactions, programs, and files....
CEMT
A transaction used by CICS administrators to inquire about and modify system resources in real-time....
Channel
A specialized processor that handles input/output operations independently from the main CPU, improving overall system performance....
CICS
IBM's transaction processing system that manages online applications and provides terminal handling, resource management, and transaction control....
CICSPlex
A CICS management facility that allows coordination and management of multiple CICS regions as a single logical entity....
CMS
The interactive component of VM operating system used for program development and testing....
COBOL
A high-level programming language designed for business applications, still widely used in mainframe environments....
Control-M
A workload automation tool from BMC Software for scheduling and managing batch jobs across enterprise systems....
Coupling Facility
Specialized hardware that provides high-speed communication and data sharing between multiple mainframe systems in a Sysplex....
Central Processor
The component in the z/OS system that the z/OS dispatcher schedules work to run on....
Change Bit
A bit associated with each frame in Central Processor Complex (CPC) memory that is turned on by the processor if any area in the page has been altered...
Ciphertext
The encrypted data. In the context of the Coupling Facility (CF), XES encrypts plaintext into ciphertext before sending it across the CF link....
Command List
A high-level programming language that enables programmers to issue lists of Time Sharing Option/Extensions (TSO/E) commands and Job Control Language ...
Common Area
A virtual storage area shared by all address spaces in a z/OS system image. Programs in this area access the same common data and programs using the s...
Console Operations
The process by which operators and system programmers interact instantaneously with z/OS to monitor or control the hardware and software....
Coupling Facility Control Code
The specialized operating system that runs on a Coupling Facility (CF)....
D
DASD
Magnetic disk storage devices that allow direct access to any data location without sequential searching. DASD is the primary online storage medium fo...
Dataset
A collection of related data records stored as a unit on mainframe storage, equivalent to a file in other operating systems. Datasets are the fundamen...
DB2
IBM's enterprise-class relational database management system for z/OS, supporting SQL and providing scalable, secure data management for mission-criti...
DCB
A control structure containing information about dataset characteristics such as record format, block size, record length, and access method. The DCB ...
DD Statement
A Job Control Language (JCL) statement that defines input/output files and datasets used by a job step or program. DD statements connect logical file ...
Dispatcher
The z/OS component that allocates CPU time to ready tasks based on priority, scheduling algorithms, and workload management policies. The dispatcher i...
DFSMS
IBM's integrated storage management system providing automated space management, backup, migration, and data protection services for z/OS. DFSMS simpl...
DRDA
A protocol enabling database communication between different platforms and DBMS products, allowing distributed DB2 access and remote SQL execution acr...
Data Definition (DD) Statement
A Job Control Language (JCL) statement used to identify and describe the input and output data to be used in a job step....
Data Space
A type of virtual storage space that can range up to 2 GB of contiguous virtual storage, entirely available for user data, but which cannot contain z/...
DES Master Key
One of the four master keys in ICSF, responsible for encrypting the Data Encryption Standard (DES) keys stored in the Cryptographic Key Data Set (CKDS...
Dialog Manager
A main component of the Interactive System Productivity Facility (ISPF) that provides services to dialogs and users, including managing display, varia...
Distributed FileManager
A function provided by z/OS Data Management services that supports access to remote data and storage resources....
Dynamic Address Translation
The process, implemented by both hardware and software, of translating a virtual address during a storage reference into the corresponding real addres...
Dynamic Configuration
The ability to change the current I/O configuration without restarting the software or performing a Power-on Reset (POR) of the hardware, typically ac...
E
EBCDIC
The character encoding scheme used by IBM mainframes to represent text characters, different from ASCII used in most other computing systems. EBCDIC u...
Enclave
A collection of related work that executes under a single service class for performance management purposes. Enclaves enable Workload Manager (WLM) to...
Enterprise COBOL
IBM's modern COBOL compiler for z/OS, supporting contemporary features like object-oriented programming, XML processing, and Java integration while ma...
ESDS
A VSAM dataset where records are stored in the order they are written, similar to sequential files but with VSAM's advanced features. ESDS provides se...
ECC Master Key
One of the four master keys in ICSF, responsible for encrypting the Elliptic Curve Cryptography (ECC) private key stored in the PKA Cryptographic Key ...
EXEC (Run) Statement
A required Job Control Language (JCL) statement that marks the beginning of a job step, assigning a name to the step and identifying the program or pr...
Extended Common Service Area
The portion of the common storage area located above the 16 MB line....
Extended Link Pack Area
A link pack area built above the 16 MB line, containing read-only system-level programs accessible by all address spaces....
Extended System Queue Area
The counterpart of the System Queue Area (SQA) located above the 16 MB line, allocated directly above the extended nucleus during Initial Program Load...
F
FTP
Standard protocol for transferring files between systems over TCP/IP networks, supported on mainframes for data exchange with distributed platforms. F...
FTPS
Secure version of FTP using SSL/TLS encryption for protected file transfers, providing confidentiality and integrity for data in transit between mainf...
G
GDG
A group of related sequential datasets organized chronologically, with each dataset called a generation. GDGs are useful for maintaining historical ve...
GDDM
IBM software for creating graphical presentations, charts, and business graphics in mainframe applications. GDDM provides graphics primitives and high...
GEAC
Enterprise resource planning (ERP) software commonly run on mainframe systems, particularly in government and utilities sectors. GEAC provides integra...
Green Screen
Colloquial term for traditional mainframe terminal interfaces, named after the green monochrome displays of early 3270 terminals. Refers to character-...
GSAM
An IMS access method for processing sequential datasets within IMS applications, providing integration between IMS transactions/programs and standard ...
H
HCD
An ISPF dialog used to define and manage I/O configuration for z/OS systems. HCD provides a centralized interface for configuring channels, control un...
Hercules
An open-source software implementation of mainframe hardware that allows mainframe operating systems (MVS, z/OS, z/VM, etc.) to run on commodity hardw...
HIPAA
Healthcare data protection regulation that many mainframe systems must comply with when processing medical information. HIPAA requires specific securi...
HLQ
The first part of a dataset name that typically identifies the owner or category of the dataset. HLQs are used for organizing datasets and controlling...
Hardware Configuration Definition
A z/OS component that consolidates the hardware and software I/O configuration processes under a single interactive user interface, producing an IODF....
High Non-shared Area
A private area in the 64-bit address space map, located above the Shared Area (starting at 250 or wherever the shared area ends) and extending to 264....
I/O Definition File
The output produced by the Hardware Configuration Definition (HCD) component, containing server, logical partition (LPAR), and I/O configuration data....
Interactive System Productivity Facility (ISPF) Dialog
An interactive application composed of a command procedure or program combined with dialog elements (panels, messages, tables) that allows an orderly ...
Internal Reader
A program that other running programs can use to submit jobs, control statements, and commands to JES2....
ISPF Workstation Agent
The client/server component of ISPF that runs on the local workstation, maintaining a connection to the ISPF host to enable the display of ISPF panels...
I
IAAS
Cloud computing model increasingly used for mainframe workload migration and hybrid architectures, providing virtualized computing resources over the ...
IDCAMS
A utility program for managing VSAM datasets, catalogs, and performing various file operations. IDCAMS (Integrated Data Cluster Access Method Services...
IDMS
A network model database management system from Broadcom (formerly CA Technologies), widely used before relational databases. IDMS uses a CODASYL netw...
IMS
IBM's hierarchical database and transaction processing system, designed for high-volume online and batch processing. IMS has been a cornerstone of ent...
IMS DB
The database component of IMS using a hierarchical data model for organizing information. IMS DB represents data as tree structures with parent-child ...
IMS DC
The transaction processing component of IMS for managing online terminal interactions and message-driven applications. IMS DC provides high-volume tra...
Initiator
A z/OS component that selects jobs from the JES input queue and allocates resources for their execution. Initiators bridge between the job entry subsy...
IOCS
The portion of the operating system that manages all input and output operations, handling physical I/O, buffering, error recovery, and device managem...
IOCP
Utility used to define I/O configuration for mainframe systems, generating IOCDS (I/O Configuration Data Set) that describes hardware configuration to...
IPL
The mainframe equivalent of booting or restarting the operating system. IPL loads the z/OS nucleus into memory and initializes the system for operatio...
ISPF
IBM's menu-driven interface for z/OS providing tools for program development, file management, and system administration. ISPF is the primary interact...
ISQL
Tool for executing SQL statements and managing DB2 databases interactively. ISQL provides an immediate feedback environment for database queries and a...
J
Java on z/OS
IBM's Java Development Kit optimized for mainframe systems, enabling modern application development using Java on z/OS. Provides full Java SE capabili...
JCL
The scripting language used to specify batch job execution on z/OS, including program names, datasets, system resources required, and execution flow. ...
JES2/JES3
The z/OS component that manages job scheduling, input/output processing, and print services. JES acts as the interface between users submitting work a...
Job
A unit of work submitted to the system for batch processing, defined by JCL statements. A job contains one or more job steps that execute sequentially...
Job Class
A categorization assigned to jobs for scheduling and resource allocation purposes. Job classes enable workload management by grouping similar jobs tog...
Job Step
An individual program execution within a job, defined by an EXEC statement in JCL. A job can contain multiple steps that execute sequentially....
JOB Statement
A required Job Control Language (JCL) statement that marks the beginning of a job, assigning it a name and providing administrative information (secur...
Job Entry Control Language
The set of command language control statements that provide information specifically for JES2 or JES3, distinct from JCL....
Link Pack Area
An area (including PLPA, FLPA, and MLPA) in the common virtual storage area containing read-only, system-level programs that are preinstalled at IPL t...
K
KSDS
A VSAM dataset where records are accessed by a unique key field, similar to indexed files....
L
LAN
Network infrastructure connecting mainframes to other systems and users within an organization....
LPAR
A virtual machine created by dividing mainframe hardware resources, allowing multiple operating system instances to run simultaneously....
LU
An SNA term for the endpoint of a communication session, typically representing a terminal or application....
Load Module
The basic unit of machine-readable executable code in a z/OS environment, created by processing one or more object modules with a link-edit utility (B...
Logical Swap
A z/OS mechanism where, when an address space is swapped out, it is removed from the processor execution queues, but recently referenced frames belong...
Low Core
A common area of virtual storage from address zero through 8191 in every address space, containing architecturally fixed hardware and software storage...
Low Non-shared Area
A private area in the 64-bit address space map, located just above the bar, typically starting at 4 GB. Private storage allocated above the bar is dra...
M
Master Catalog
The primary catalog that contains entries for all user catalogs and critical system datasets....
MFA
Security enhancement increasingly implemented on mainframe access points for stronger authentication....
MICS
Performance monitoring and reporting software for mainframe environments....
Middleware
Software that connects different applications and services, facilitating communication between mainframe and distributed systems....
Migration
The process of moving applications, data, or entire systems from mainframes to modern platforms or updating to newer mainframe technologies....
MIPS
A measure of mainframe processing capacity, used for licensing and capacity planning....
MQ Series
Message queuing middleware enabling asynchronous communication between applications across different platforms....
MSU
IBM's metric for measuring mainframe workload, used for software licensing costs....
Multiprocessing
The execution of more than one task simultaneously on multiple processors (or mains), all operating under a single copy of z/OS and sharing the same m...
Multiprogramming
A system environment where many tasks can exist concurrently, each running programs in its own address space. In a single-processor configuration, onl...
Nucleus
The read-only area of common storage containing the z/OS kernel programs and extensions, initialized during Initial Program Load (IPL)....
Object Module
The output from a language translator (assembler or compiler), composed of control sections (CSECTs)....
N
Natural
A fourth-generation programming language from Software AG, commonly used with ADABAS database....
NetView
IBM's network management tool for monitoring and managing mainframe networks and resources....
NFS
Protocol allowing mainframes to mount and access file systems on UNIX and Linux servers....
O
OLTP
Real-time transaction processing systems like CICS and IMS that handle high volumes of short transactions....
OMEGAMON
IBM's monitoring and management software for mainframe systems, databases, and middleware....
Operator Console
The interface used by system operators to monitor system status and respond to messages and alerts....
OPC
Job scheduling software for automating batch processing workflows....
P
Parallel Sysplex
A cluster of z/OS systems working together as a single system, providing high availability and workload balancing....
Partitioned Dataset
A dataset containing multiple members (files), commonly used for storing program libraries and JCL procedures....
PDSE
An enhanced version of PDS with improved performance and no directory size limitations....
PL/I
A general-purpose programming language developed by IBM, combining features of COBOL, FORTRAN, and ALGOL....
Page Fault
A program interrupt caused by the hardware during dynamic address translation (DAT), indicating that the requested page is not currently mapped to a f...
Page Stealing Algorithm
An algorithm used by the Real Storage Manager (RSM) to replenish the supply of available CPC memory frames when the supply runs low. It selects frames...
Paging
The movement of 4 KB pages between Central Processor Complex (CPC) memory frames and auxiliary storage slots. This involves two operations: Page-in (s...
PKA Cryptographic Key Data Set
A secure repository managed by ICSF that stores RSA and Elliptic Curve Cryptography (ECC) key pairs, encrypted by the RSA or ECC Master Key....
Plaintext
The original, unencrypted data....
Processing Unit
The hardware responsible for running instructions located in Central Processor Complex (CPC) memory; contains facilities for instruction execution, in...
Q
R
RACF
IBM's security software providing user authentication, authorization, and auditing for z/OS systems....
RDO
The process of defining CICS resources dynamically without requiring system restart....
Reentrant
A program attribute allowing multiple users or tasks to execute the same code simultaneously without interference....
Rehosting
Migration strategy that moves mainframe applications to new platforms with minimal code changes, often using emulation....
Replatforming
Migration approach that involves some optimization while moving to new platforms, falling between rehosting and refactoring....
REXX
A scripting language for z/OS, used for automation, system administration, and application development....
RRDS
A VSAM dataset where records are accessed by relative record number position....
RACROUTE Macro
The macro issued by a z/OS component or subsystem to use the z/OS router for System Authorization Facility (SAF) calls....
Real Storage Manager
The z/OS component that controls the usage of Central Processor Complex (CPC) memory frames. RSM manages paging activities, such as page-in, page-out,...
Reference Bit
A bit associated with each frame in Central Processor Complex (CPC) memory that the system checks at regular intervals to see if the frame has been re...
Region
In a 64-bit address space, virtual storage is partitioned into regions, typically 2 GB in size....
Region Tables
Three additional levels of Dynamic Address Translation (DAT) tables (Region First, Second, and Third Tables) defined in the z/Architecture for transla...
Restructured Extended Executor (REXX) Exec
A structured program written in REXX, a high-level procedures language that enables logical and arithmetic operations....
S
SDF
Tool for designing and creating screen layouts for mainframe applications....
SDLC
An IBM protocol for communication over synchronous serial connections....
Sequential Dataset
A dataset where records are stored and accessed in sequential order, like a flat file....
SDSF
A tool for viewing and managing job output, system logs, and JES resources....
SMF
z/OS component that collects system performance and accounting data for analysis and reporting....
SMP/E
IBM's tool for installing and maintaining z/OS system software and maintenance updates....
SNA
IBM's proprietary networking architecture for mainframe communications, largely replaced by TCP/IP....
SOR
The authoritative source for specific data, often maintained on mainframe systems for critical business information....
SPOOL
Storage area for holding job output until it can be processed or printed....
Step Condition Code
A numeric value returned by each job step indicating success (0) or various error conditions (non-zero)....
Subsystem
A component of z/OS that provides specific services, such as JES, DB2, or CICS....
Sysplex
A collection of z/OS systems working together, sharing workload and resources for high availability....
ServerPac
An entitled software delivery package where IBM has performed the SMP/E installation steps and some post-SMP/E steps, with service integrated with the...
Shared Area
An area in the 64-bit address space map designed for shared memory, starting at 241 (2 TB) and potentially going up to 253 (512 TB)....
Software Configuration and Library Manager
An ISPF software tool that helps develop complex software applications by automatically controlling, maintaining, and tracking all software components...
Source Module
The input provided to a language translator (assembler or compiler)....
Storage-Class Memory
The storage provided by Virtual Flash Memory (VFM), used by z/OS for paging (4K and larger pages) and for staging SAN Volume Controller (SVC) dumps....
Symmetric Cryptography
A method where the same key is used to encrypt and decrypt data....
SYSOUT
System-produced output; all output produced by, or for, a job, including system messages and user-requested data sets destined for printing or punchin...
System Area
An area in the 64-bit address space map designed for system storage, starting at 2**35 (32 GB) and extending up to 288 GB....
SystemPac
A software package available for an additional fee where IBM performs customized installation of z/OS and various subsystems (like DB2, IMS, CICS) bas...
T
Task
A unit of work being executed by the operating system, equivalent to a process or thread in other systems....
TCP/IP
The standard networking protocol suite used for mainframe connectivity to modern networks....
Tape Drive
Sequential storage device using magnetic tape, still used for backup and archival purposes....
TCPIP
z/OS component providing TCP/IP networking capabilities for internet connectivity....
TSO
Interactive component of z/OS allowing users to execute commands and programs from terminals....
Terminal Communications Access Method
The primary TSO/E address space in a VTAM environment, which receives the LOGON command from VTAM....
Translation Lookaside Buffer
A hardware buffer used to accelerate the Dynamic Address Translation (DAT) process if the virtual address is already mapped in Central Processor Compl...
Trusted Key Entry (TKE) Workstation
A dedicated workstation used to enter the Master Keys into the tamperproof Crypto Express hardware....
Unreferenced Interval Count
A counter associated with a frame in Central Processor Complex (CPC) memory that indicates how long it has been since a program referenced that page. ...
User Attribute Data Set
A data repository that can be used to define users to TSO/E, storing their user ID, logon procedure name, and TSO/E resource authority....
User Region
The portion of the address space private area available to the user's programs....
U
V
Virtual Storage
Memory management technique where programs see a larger address space than physical memory available....
VM
IBM's operating system for creating and managing virtual machines on mainframe hardware....
VSAM
IBM's file system for z/OS, providing indexed, sequential, and relative record access methods....
Virtual Flash Memory
The next generation of Storage Class Memory (SCM) designed to improve availability and performance, particularly for reducing latency during paging sp...
Virtual I/O
A function that handles temporary data sets (work files) by placing them in external page storage, making them appear to the program as if they were o...
Wait State
The condition of a task when it is waiting for an event (such as an I/O operation) to occur, meaning it is not currently a candidate to receive contro...
W
X
Z
Related Terms:
- **Legacy System Modernization**: The process of updating or replacing outdated mainframe systems - **Hybrid Cloud**: Architecture combining mainfram...
Common Acronyms:
- **CA**: Computer Associates (now Broadcom) - **BMC**: BMC Software (provider of mainframe tools) - **ISV**: Independent Software Vendor - **PTF**: P...
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