routines. They can run on different computers with little or no modification.

PDS. 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. Contrast with sequential data set.

PDSE. 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.

peer. (1) In network architecture, any functional unit that is in the same layer as another entity. (2) A corresponding node or entity.

physical IOCS (PIOCS). Supervisory routines that schedule and supervise the execution of channel programs. Physical IOCS controls the actual transfer of records between external storage and main storage, and provides I/O device error recovery.

physical record. (1) A record whose characteristics depend on the manner or form in which it is stored, retrieved, or moved. A physical record may contain all or part of one or more logical records. (2) The amount of data transferred to or from auxiliary storage. Synonymous with block.

portability. (1) The capability of a program to be executed on various types of data processing systems without converting it to a different language and with little or no modification. (2) The ability to run a program on more than one computer without modifying it. (3) Synonymous with transportability.

POWER. A VSE program used to spool input and output. It also allows exchange of files with, or job runs on, a remote processor Originally an acronym for Priority Output Writer Execution and Reader.

procedure. A named block of code that can be invoked, usually via a call.

PR/SM. Processor Resource / Systems Manager

precompile. To process programs containing SQL statements before they are compiled. SQL statements are replaced with statements that will be recognized by the host language compiler. The output from this precompile includes source code that can be submitted to the compiler and used in the bind process.

preventive maintenance. (1) Maintenance performed specifically to prevent faults from occurring. (2) Contrast with corrective maintenance.

private address space. An address space assigned to

a particular user.

problem determination. The process of determining the source of a problem; for example, a program component, machine failure, telecommunication facilities, user or contractor-installed programs or equipment, environmental failure such as a power loss, or user error.

procedural language. A programming language in which computations are expressed in terms of statement sequences; for example, Pascal. Synonym for procedure-oriented language.

procedure. In a programming language, a block, with or without formal parameters, whose execution is invoked by means of a procedure call.

procedure library. A program library in direct access storage with job definitions. The reader/interpreter can be directed to read and interpret a particular job definition by an execute statement in the input stream.

processor storage. (1) The storage provided by one or more processing units. (2) In virtual storage systems, synonymous with real storage.

PROCLIB. procedure library. A program library in direct access storage with job definitions. The reader/interpreter can be directed to read and interpret a particular job definition by an execute statement in the input stream.

program. A sequence of instructions suitable for processing by a computer. Processing may include the use of an assembler, a compiler, an interpreter, or a translator to prepare the program for execution, as well as to execute it.

program offering. An unwarranted licensed program. See also vendor-logo product.

program product. Deprecated term for licensed

program.

programmer logical unit. In VSE, a logical unit available primarily for user-written programs.

programming language. An artificial language for expressing computer programs.

programming system. (1) In a programming environment, the software required for the development and use of computer programs. (2) In a data processing system, the software needed to use one or more programming languages.

PSF. Print Services Facility. A licensed program that manages and controls the input data stream and output data stream required by supported IBM page printers. PSF combines print data with other resources and printing controls to produce AFP output. There are PSF products for MVS (OS/390), VSE, RS/6000 and OS2 platforms.

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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.