z/OS subsystems

The IBM mainframe environment is driven and controlled by the z/OS operating system. However, applications are using different subsystems, designed for specific purposes. During this course participants learn to describe the functions and main components of the following important z/OS subsystems:

  • they learn how terminal/user interaction is done using transaction monitors like CICS Transaction Server (CICS TS) and IMS Transaction Manager (IMS TM);
  • they will understand how databases are serving applications, based on a hierarchical model (IMS DM) or on a relational architecture (Db2);
  • they become familiar with the Unix System Services (USS) on the mainframe;
  • they will understand the importance of a message queuing system (MQ) for connecting (distributed) applications;
  • and finally, they will get some insight in the possibilities of the WebSphere Application Server and related services for handling web based applications, or Java EE workload, or business services, or ...

In addition, participants will get an overview of the management aspects for all these subsystems, and will be able to describe the safety- and integrity-aspects.


No public sessions are currently scheduled. We will be pleased to set up an on-site course or to schedule an extra public session (in case of a sufficient number of candidates). Interested? Please let us know.

Intended for

Everyone in the systems department who wants a general introduction to the z/OS subsystems. Especially for DP managers, system programmers, system analysts and operators.


A basic mainframe background is required (see Mainframe computing introduction).

Main topics

  • CICS overview - the most important components and facilities of transaction processing in a CICS system.

Terminal control • dataset manipulation • error treatment • resource management • interprogram communication • monitors • development tools.

Communication between programs and database management systems and/or message queues.

System management: description of possible error situations • recovery and restart facilities • synchronisation and security • distributed CICS facilities • CICSPLEX

  • The hierarchical database management system (IMS/DM)

hierarchical structures • physical organisations of databases • the most important control blocks (DBD and PSB) • application interface DL/1 • secondary indexes and logical relations

  • The data communication system (IMS/TM)

tasks of the DC monitor • internal set-up • conversational versus non-conversational applications • synchronisation and security

  • Relational Databases (Db2)

what is an RDBMS • how do applications use Db2 (static vs dynamic, drivers) • Db2 system objects • Db2 from the OS system point of view (setup, address spaces, ...) • Db2 and security • distributed Db2, DDF, DRDA, Connect • Db2 family

  • UNIX System Services (USS)

Understand the position of USS within the OS • USS as a Unix shell • USS user interfaces • HFS • Irish commands • security • USS and TSO, USS and JCL • monitor USS activity • software that depends on USS: TCPIP, Web Server, JVM, WebSphere Application Server

  • Message queuing systems (MQ)

Concepts of queuing • distributed topology • WMQ objects, communication, shared queues, clusters • WMQ from the OS system point of view (setup, address spaces, ...) • MQ application behaviour • MQ bridges

  • WebSphere Application Server (WAS)

WAS as a Java EE runtime • WAS administrative architecture and repository • application flow in the server • application deployment and maintenance • relationship with HTTP server, CICS, MQ, IMS, Db2 • WAS from the OS system point of view (setup, address spaces, ...) • WAS topologies for load balancing and availability

Training method

Classroom instruction with numerous demos.


3 days.

Course leader

Koen De Backer.