z/OS

z/OS
Name	z/OS
Developer	IBM
Source model	Closed source
Released	03 October 2000
Latest release version	2.5
Latest release date	14 September 2021
Marketing target	Mainframe environments
Kernel type	Monolithic kernel
License	Proprietary software
Website	https://www.ibm.com/it-infrastructure/z/zos

z/OS. It is a 64-bit operating system designed by IBM for its family of z/Architecture mainframe computers. As the primary operating system for the IBM Z platform, it is renowned for its exceptional availability, scalability, and security, supporting critical, high-volume transaction processing and large-scale database management. z/OS builds upon decades of mainframe evolution, integrating traditional strengths with modern capabilities like support for Java, UNIX System Services, and TCP/IP.

Overview

z/OS serves as the cornerstone for enterprise IT infrastructure in major industries such as banking, insurance, and airline reservation systems. It provides a highly secure and stable environment for running essential business applications, often built with languages like COBOL and PL/I. The system's design emphasizes backward compatibility, ensuring that applications developed for earlier systems like MVS and OS/390 continue to operate. This reliability makes it a preferred platform for hosting core systems at institutions like Citibank, JPMorgan Chase, and many global clearing houses.

History

The lineage of z/OS traces directly to OS/360, introduced by IBM in the 1960s. Its immediate predecessor was OS/390, which unified several mainframe operating system families. z/OS was officially launched in October 2000, coinciding with the introduction of the 64-bit z/Architecture with the IBM zSeries 900. Key milestones in its development have included the integration of UNIX-style interfaces via UNIX System Services, enhanced support for Internet protocols, and the adoption of Java and Linux interoperability. Each release, managed through IBM Software Support, has added functionality while preserving the investment in existing applications.

Architecture

The architecture of z/OS is built around the principles of the z/Architecture instruction set, which provides extensive memory virtualization and address space capabilities. A fundamental concept is the use of multiple virtual storage spaces and sophisticated I/O management through the Multiple Virtual Storage (MVS) nucleus. The system employs a monolithic kernel but structures operations into distinct subsystems like the Workload Manager (WLM) and the System Resource Manager (SRM). Critical architectural features include Parallel Sysplex technology for clustering, which enables near-continuous availability across systems, and support for logical partitions (LPAR) managed by the PR/SM firmware.

Key components

Several core subsystems define the z/OS environment. The Job Entry Subsystem (JES2 or JES3) controls job scheduling and print/output management. For transaction processing, the Customer Information Control System (CICS) and Information Management System (IMS) are pivotal. The z/OS Communications Server implements robust TCP/IP and SNA networking stacks. Database management is primarily handled by IBM Db2 and IMS Database. Other essential components include the Time Sharing Option (TSO) for interactive users, the z/OS UNIX System Services shell, and the Resource Access Control Facility (RACF) for security.

Security features

Security is a paramount design goal, achieved through multiple integrated features. The Resource Access Control Facility (RACF) serves as the primary access control and audit subsystem, managing user identities and authorizations. z/OS supports advanced cryptography via the CPACF and zIIP specialty engines, and provides facilities for PKI services and SSL/TLS. The system offers rigorous mandatory access control and detailed security event logging, which are critical for compliance with regulations like the Payment Card Industry Data Security Standard (PCI DSS) and the Sarbanes–Oxley Act.

Usage and applications

z/OS is deployed globally for the most demanding commercial workloads. It is the platform of choice for core banking systems at financial giants like Bank of America and HSBC, processing billions of daily transactions through systems like CICS and ATM networks. Major airline reservation systems, such as Sabre and Amadeus, rely on its high availability. It also hosts massive Db2 databases for retailers, runs complex batch processing for insurance companies like AIG, and serves as a secure enterprise server for cloud computing environments and hybrid infrastructure.

Category:IBM mainframe operating systems Category:Proprietary operating systems Category:2000 software