# z/OS

> 64-bit operating system for IBM mainframes

**Wikidata**: [Q283705](https://www.wikidata.org/wiki/Q283705)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Z/OS)  
**Source**: https://4ort.xyz/entity/z-os

## Summary
z/OS is a 64-bit operating system developed by IBM specifically for its mainframe computers. Published in 2001 as the successor to OS/390, it is classified as a Unix-like operating system and is certified under the Single UNIX Specification.

## Key Facts
- **Developer:** IBM (International Business Machines Corporation).
- **Platform:** Designed for the z/Architecture.
- **Initial Publication:** 2001.
- **Current Version:** 3.1 (released September 29, 2023).
- **Programming Language:** Written in PL/X (Programming Language/Cross Systems).
- **Certification:** Single UNIX Specification.
- **Predecessor:** Replaced the OS/390 operating system; also known by the alias MVS.
- **Filesystems:** Supports zFS and the Episode filesystem, both of which are POSIX-compliant.
- **Core Components:** Includes UNIX System Services and System Managed Storage.

## FAQs
### Q: What hardware platform does z/OS require?
A: z/OS is designed to run exclusively on IBM mainframes using the z/Architecture platform.

### Q: Is z/OS considered a Unix system?
A: Yes, it is an instance of a Unix-like operating system and is officially certified under the Single UNIX Specification. It includes UNIX System Services, which was implemented in 2001.

### Q: What is the most recent version of z/OS?
A: The most recent version is z/OS 3.1, which was released on September 29, 2023.

### Q: What programming languages are associated with z/OS?
A: The system is developed using PL/X and supports various other languages and tools including CLIST, Simula, and the CICS transaction management application.

## Why It Matters
z/OS is the primary 64-bit operating system for IBM's mainframe environment, serving as a critical evolution of the earlier MVS and OS/390 systems. Its significance lies in its ability to combine traditional mainframe strengths with modern open standards. By achieving Single UNIX Specification certification and integrating UNIX System Services, z/OS provides a bridge between proprietary mainframe reliability and the portability of Unix-like environments.

The system manages massive enterprise workloads through specialized components like System Managed Storage and the CICS customer data and transaction management application. It utilizes sophisticated data structures, such as the "catalog," which maps dataset names to volumes to ensure efficient data handling. Furthermore, its support for diverse programming languages—ranging from the internal PL/X to Simula—and application generators like the IBM Cross System Product, makes it a versatile foundation for large-scale computing. As a POSIX-compliant environment utilizing the zFS filesystem, z/OS remains a central pillar of IBM's technology portfolio, continuing to receive major updates like the 2023 release of version 3.1.

## Notable For
- **64-bit Architecture:** Specifically optimized for high-performance IBM z/Architecture mainframes.
- **Single UNIX Specification:** Certified to meet industry standards for Unix-like operating systems.
- **UNIX System Services:** A native implementation of UNIX within the z/OS environment, launched in 2001.
- **Proprietary Systems Language:** Built using PL/X (Programming Language/Cross Systems), an internal IBM systems programming language.

## Body

### Development and History
z/OS was created by IBM, a multinational corporation founded in 1911 and headquartered in Armonk, New York. The operating system was first published in 2001 to replace OS/390. It has evolved through several major versions, including version 2.5 (released September 30, 2021) and the current version 3.1 (released September 29, 2023).

### Technical Specifications
The operating system runs on the z/Architecture platform. It is distinguished by its 64-bit capabilities and its adherence to the Single UNIX Specification.
*   **Internal Language:** The system is primarily developed using PL/X.
*   **Filesystems:** It utilizes zFS, a POSIX-compatible filesystem, and the Episode filesystem, which is also POSIX-compliant.
*   **Data Structure:** It employs a "catalog" on-disk data structure, inherited from OS/360, to map dataset names to specific volumes.

### Components and Integration
z/OS integrates several key IBM technologies to manage data and applications:
*   **UNIX System Services:** This component provides a UNIX implementation directly on the z/OS platform.
*   **Transaction Management:** It supports CICS, an application for customer data and transaction management that dates back to 1968.
*   **Storage Management:** It includes System Managed Storage as a core part of the operating system.
*   **Application Standards:** It follows the IBM Systems Application Architecture, a set of standards established in 1987.

### Related Systems and Software
z/OS exists alongside other mainframe operating systems and tools:
*   **Related Operating Systems:** These include Hitachi's VOS3 and VOS, Fujitsu's OSIV/MSP, and the Special Real Time Operating System for IBM mainframes.
*   **Supported Tools:** The system runs CLIST, Simula, and the IBM Cross System Product (an application generator).

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## References

1. [Source](https://www.ibm.com/common/ssi/ShowDoc.wss?docURL=/common/ssi/rep_ca/0/897/ENUS221-260/index.html&lang=en#availx)
2. [Source](https://www.ibm.com/support/pages/zos310)
3. Freebase Data Dumps. 2013
4. BabelNet