Glossary

Numerics

2-digit-year format. A format that provides a year date as two digits only to represent a year within a specific century. The two high-order digits of the year are truncated; for example 1995 is represented as 95.

4-digit-year format. A format that provides a year date as four digits: the two high-order digits represent the century and the two low-order digits represent the year within the century. For example, 1995 represents the year 1995; 2095 represents the year 2095.

20th century. The period of time 0000.00 hrs 1901-January-1 through 2400.00 hrs

2000-December-31.

21st century. The period of time 0000.00 hrs 2001-January-1 through 2400.00 hrs

2100-December-31.

24-hour clock. A clock that keeps time from 0000 (midnight) to 1200 (noon) and from 1200 (noon) to 2400 (midnight). Compare with 12-hour clock.

3270 emulation. The use of a program that allows a device or system such as a personal computer to operate in conjunction with a host system as if it were a 3270- series display station or control unit.

A

abend code. A system code that identifies the system message number and type of error condition causing the abend.

abnormal termination. (1) The cessation of processing prior to planned termination. (2) A system failure or operator action that causes a job to end unsuccessfully.

access control. In computer security, ensuring that the resources of a computer system can be accessed only by authorized users in authorized ways.

access level. In computer security, the level of authority a subject has when using a protected resource; for example, authority to access a particular security level of information.

access method. A technique to obtain the use of data, storage, or the use of an input/output channel to transfer data; for example, random access method, sequential access method.

access method routines. Routines that move data between main storage and input/output devices.

Access Method Services (AMS). A utility program (named IDCAMS) that defines VSAM data sets (or files), allocates space for them, modifies attributes, and manipulates data sets and catalog entries.

access mode. The way a file is used within a job step, a program, or a module. Most access modes correspond to OPEN modes specified in OPEN statements (such as input, output, or update).

access path. A sequence of data items used by a database management system to access records or other data items stored in a database. There may simultaneously exist more than one access path for one data item.

account file. A direct access file maintained by VSE/POWER to hold the accounting information it generates and the programs that it controls.

actual conversion. The conversion of source material done at the end of migration, in order to switch over from VSE to MVS. (Contrast with dummy mass conversion.)

AD/Cycle. An IBM product that offers an enterprise modeling approach supported by tools that will assist in the creation of an enterprise model to be validated, analyzed, and then used to generate applications. It consists of a framework for, and a set of, application development tools provided by an Application Development (AD) platform, designed to support the integration of tools through a consistent user interface, workstation services, an AD information model, tool services, Repository Services, and Library Services. It provides control for defining and sharing application development data.

address space. (1) The range of addresses available to a computer program. (2) The complete range of addresses that are available to a programmer. See also virtual address space. (3) In VSE, a subdivision of the total of virtual storage if the computer system operates in 370 mode.

address translation. In virtual storage systems, the process of changing the address of an item of data or an instruction from its virtual storage address to its real storage address.

AFP. Advanced Function Presentation. A set of licensed programs, together with user applications, that use the all-points-addressable concept to print on presentation devices. AFP includes creating, formatting, archiving, retrieving, viewing, distributing, and printing information.

AFPDS. AFP data stream. A presentation data stream that is processed in AFP environments.

© Copyright IBM Corp. 1998

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OS/390 specifications

IBM OS/390, a versatile operating system, was a cornerstone in enterprise environments and played a pivotal role in mainframe computing. Released in the mid-1990s, OS/390 combined the strengths of IBM's MVS (Multiple Virtual Storage) with new features and enhancements, targeting scalability, reliability, and performance in demanding business applications.

One of the key features of OS/390 was its robust support for multiple users and processes. The system allowed thousands of concurrent users to access applications and data, ensuring high availability and minimizing downtime—a critical requirement for many large organizations. This scalability was supported through various enhancements in memory management and processor scheduling, enabling optimal resource allocation across diverse workloads.

OS/390 was known for its superior workload management capabilities. The Workload Manager (WLM) component allowed administrators to define service policies, specifying how system resources would be allocated according to the priority of tasks. This ensured that critical business processes received the necessary resources while less critical tasks were managed more flexibly.

Another significant characteristic of OS/390 was its commitment to security. The operating system provided comprehensive security features, including user authentication, data encryption, and auditing capabilities. This focus on security was vital for organizations handling sensitive data, ensuring compliance with regulations and safeguarding against unauthorized access.

OS/390 also supported advanced technologies that facilitated integration and development. The system included features like the IBM CICS (Customer Information Control System) for transaction processing and IMS (Information Management System) for database management. These technologies allowed organizations to build robust, high-performance applications tailored to specific business needs.

The ease of network integration was another strength of OS/390. With the advent of the Internet and global connectivity, OS/390 systems could easily interface with various network protocols, enabling businesses to operate in a connected world. This inclusion paved the way for many organizations to expand their capabilities and offer new services, driving digital transformation.

In conclusion, IBM OS/390 represented a significant advancement in mainframe technology, combining scalability, security, and robust workload management. Its rich feature set and support for critical enterprise applications solidified its role as a vital component of many organizations' IT infrastructures, ensuring they could meet their operational challenges head-on while supporting future growth. As technology continues to evolve, the legacy of OS/390 remains influential in the realm of computing.