Understanding the mainframe ecosystem can take time, but understanding the basic building blocks and components within the mainframe today can help early-career Z professionals excel. Roger Bales, program director for z/OS strategy at IBM, and Christina LaRow, client adoption specialist at IBM, explored these key elements in their SHARE Washington, D.C., session, “Demystifying How z/OS Works for Early-Career Z Professionals.”
With a high-level overview of the IBM z/Architecture, its operating systems, and their core components, early-career mainframers can use advanced virtualization technologies, learn how to maximize compute resources, and understand the key services that power large-scale business applications.
z/Architecture
At the heart of every mainframe system is the z/Architecture. It is the set of instructions and rules that define how a mainframe computer is designed and functions. For z, it's the plan for the entire system, including its hardware, software, and the way it interacts. The architecture includes the instruction set, memory management, I/O, communications, and compatibility. All of this enable mainframes to execute programs that provide the business value of today’s mainframe systems.
“Understanding how this architecture works is essential, as it allows you to grasp the underlying hardware and software interactions that drive mainframe operations,” according to Bales and LaRow. For example, when adding two fields, the architecture will lead the machine to access and execute the relevant instructions quickly, efficiently, and reliably.
Address Spaces and Secure Isolation
Mainframe systems provide secure isolation by using address spaces, which are essential for managing memory and ensuring data integrity. Each address space is where contiguous virtual addresses are available for executing instructions and storing data for a running program, and multiple address spaces can operate simultaneously without interfering with each other. It's like a virtual map that provides each program with a separate area to store its code and data, isolating it from other programs and the operating system. “This isolation is a critical feature for maintaining the security and integrity of sensitive data, especially in multi-user environments,” they explain.
Service-Level Agreements (SLAs) and Workload Management
Mainframe systems often operate under strict service-level agreements (SLAs), ensuring that workloads are processed efficiently and within predefined timeframes. Early-career professionals should understand how to configure and manage workloads through z/OS Workload Manager (WLM). WLM prioritizes specific tasks and ensures that it is prioritized in an optimal way. Less time-sensitive tasks are deferred. According to Bales and LaRow, “This is particularly important for enterprises that rely on mainframes for a variety of applications from payroll to inventory management.”
System Enhancement and Base Control Programs
“Mainframe systems are continuously enhanced to keep up with evolving technologies,” say Bales and LaRow. The base control program (BCP) is responsible for managing I/O operations and providing fundamental control over the system. “Understanding how this program interacts with hardware is crucial for troubleshooting and optimizing mainframe performance,” they explain. Additionally, the system management facility (SMF) can be used to track system information and generate reports, enabling system administrators to monitor and fine-tune performance.
Security: RACF and SAF
Mainframe security is a top priority for enterprises, and early-career professionals should be well-versed in the resource access control facility (RACF). RACF provides identification, authentication, access control, and logging services. RACF works alongside the system authorization facility (SAF) to deliver strong security capabilities. SAF is how resource managers (TSO, IMS, CICS, Db2, DFSMSdfp, etc.) make requests of the External Security Manager (ESM), which can be RACF, ACF2 or Top Secret. Bales and LaRow point out that “it’s important to understand not only the ESM in use, but also the structure and nature of security on z/OS, as well as the basic generally accepted security principles (“Defense in Depth,” “Least Privilege,” “Dual Control,” etc.). Professionals that understand how RACF handles authorization and access control are on their way to learning how to maintain a secure mainframe environment.”
Operating Systems and Middleware
The mainframe operating system, typically z/OS, forms the foundation upon which all other applications and middleware run. “Without the operating system, nothing on the system can function,” they say. Middleware, such as CICS, IMS, MQ, and Db2, is essential for enabling communication between the operating system and applications. Middleware allows applications to run smoothly on the mainframe by facilitating data transfer, transaction management, and database access. Bales and LaRow indicate that “early-career professionals should become familiar with these middleware components, as they often form the backbone of critical business applications.”
Datasets and Data Management
Mainframe data management revolves around data sets, which are files that can be sequential, partitioned, indexed, or accessed directly by record number. Datasets store data and are often referred to as files. Some dataset formats can be partitioned to contain multiple members. Understanding the different types of datasets and their optimal use cases — such as VSAM (Virtual Storage Access Method) for application data — will help mainframers more efficiently work with data.
Mainframe datasets are stored in volumes, and these volumes harken back to a time when data was stored on media, such as physical disk drives (direct-access storage devices - DASD) or magnetic tape. Today, a volume may be virtualized and while appearing as a volume to z/OS, the data may now be stored in technology such as flash or even on cloud. Each volume has a volume table of contents (VTOC), which keeps track of the datasets stored within it. The catalog plays a critical role in managing these datasets and volumes. Catalogs help organize datasets and provide a way for the system to locate them, and those can include master catalogs and user catalogs.
A master catalog is a VSAM data set that acts as a central repository, containing entries for all user catalogs and aliases, enabling the system to locate and manage data sets efficiently. A user catalog stores the name and location (volume/unit) of data sets, allowing users to access them without needing to know their physical location, which Bales and LaRow say, “simplifies backup and recovery procedures.” They add, “There is no structural difference between a master catalog and a user catalog. What makes a master catalog different is how it is used, and what data sets are cataloged within it. Each system has one active master catalog.” System Managed Storage (SMS) is another essential tool that automates data placement, backup, migration to tape, and encryption, among other tasks to simplify storage management.
Job Control Language (JCL) and Batch Processing
Job control language (JCL) is used to manage batch jobs in mainframe environments. JCL allows administrators to control the execution of jobs, ensuring that they run correctly and efficiently. How to write and optimize JCL scripts is crucial for automating tasks and managing workflows.
Online Transaction Processing (OLTP)
Mainframes are also used for online transaction processing (OLTP), which enables real-time transactions, such as ATM withdrawals or flight bookings. OLTP systems require low-latency, high-throughput processing and often rely on middleware to manage transactions between users and the database. “OLTP is performance-sensitive, and understanding how to optimize these processes is essential for anyone working with mainframe applications,” Bales and LaRow explain.
Unix System Services (USS) and Modern Application Integration
Mainframe systems offer access to Unix environments through Unix System Services (USS). USS provides interactive access to z/OS via tools like iSHELL and zFS, enabling users to interact with the system using Unix commands. Additionally, container extensions allow Linux applications to run on z/OS, providing even greater flexibility. As modern applications increasingly require integration with mainframes, Bales and LaRow say, “Many early-career professionals are likely already comfortable using Unix commands and interacting with Linux. And they can use these industry-standard tools to bridge the gap between traditional and modern computing environments.”
Basic Building Blocks Provide a Platform for Career Growth
“With a vast majority of critical workloads and applications that enable our daily global life running on mainframes, there are great career opportunities with the IBM Z mainframe,” say Bales and LaRow. A focus on gaining expertise in these foundational elements from z/architecture, job management, and system storage to security protocols is key to career growth. By understanding how these components work together, new-to-Z professionals can accelerate their careers and contribute to the continued success of mainframe systems in the enterprise world. Mastering these concepts will position professionals to thrive in a technology landscape where mainframes continue to evolve and remain critical to business operations.