IBM Z and z/OS Fundamentals

IBM Z is a highly secure, connected, and cognitive computing platform renowned for its reliability, scalability, and availability. It is engineered to manage a large percentage of the world's mission-critical business data and transactions, from banking to healthcare. As a mature environment, the IBM Z platform provides an extensive set of features and functions proven to support the most demanding enterprise workloads. This architecture serves as the bedrock for the high-performance transaction processing and data serving for which the mainframe is known.

The z/OS operating system is a 64-bit operating system that works in conjunction with the IBM Z architecture to manage system resources and run applications. IBM delivers a new z/OS release every two years to introduce new functions and enhancements; for example, z/OS V2R1 was made generally available on September 30, 2013, followed by V2R2 on September 30, 2015, and V2R3 on September 30, 2017. This regular cadence ensures the platform evolves to meet modern enterprise demands while maintaining its core principles of stability and security.

The z/OS system provides comprehensive solutions across several major service areas, including:

• **Data management**: z/OS offers a set of functions to manage storage resources, support data storage and retrieval on disk, optical, and tape devices, and supply device management functions to control I/O devices. It also provides program management functions, and its Distributed FileManager (DFM) supports access to remote data resources. These services form the foundation for the platform's ability to handle vast quantities of enterprise data efficiently and reliably.

• **z/OS UNIX system services**: This component provides a UNIX-compliant environment, including a kernel, shell, and utilities fully compliant with the X/Open Portability Guide (XPG) 4.2 standard. It leverages the Language Environment to support industry standards for C programming, enabling application portability from other UNIX platforms. This integration allows z/OS to run a powerful combination of traditional mainframe applications and open systems workloads simultaneously.

• **Distributed computing services**: These services allow z/OS to act as a file server in an Internet Protocol network through the Network File System (NFS), enabling remote files to appear as local files on a client system. Additionally, Distributed File Services (DFS) system-managed buffering (SMB) enables data access across various platforms and automatically handles the conversion between American Standard Code for Information Interchange (ASCII) and Extended Binary Coded Decimal Interchange Code (EBCDIC). This capability is crucial for integrating the mainframe into heterogeneous enterprise IT environments.

A z/OS system programmer is responsible for the implementation, customization, and maintenance of the z/OS operating system environment. Their key tasks include planning daily system operations, managing software products, and transforming security policy objectives into a usable plan to ensure the security, availability, and integrity of the system. System programmers also provide technical support to users, which can involve answering questions about a product or analyzing potential software defects, making their role central to the stability and performance of the entire platform.

The Language Environment is a common runtime environment for applications written in high-level languages such as C, C++, COBOL, and PL/I. It combines essential services like runtime message handling, condition handling, and storage management into a single, consistent framework. By removing most system dependencies, the Language Environment allows for the easier creation of mixed-language applications and ensures consistent behavior across different programming languages, which is fundamental to both modernizing legacy applications and developing new ones.