A z/OS® system might appear to be one big block of code that drives the CPU. Actually, z/OS is a complex system comprising many different smaller blocks of code, and that's how SMP/E sees z/OS.

Each of those smaller blocks of code perform a specific function within the system. Functions that can appear in a z/OS system (some of which are shown in Figure 1) include:

• Base Control Program (BCP)
• Job entry subsystem (JES2 or JES3)
• Time Sharing Option/Extensions (TSO/E)
• Interactive System Productivity Facility (ISPF)
• System Display and Search Facility (SDSF)
• Data Facility Storage Management Subsystem (DFSMS™)
• System Modification Program Extended (SMP/E)
• z/OS UNIX® System Services (z/OS UNIX)
• Resource Measurement Facility (RMF™)
• HTTP Server
• DB2® for z/OS
• Customer Information Control System (CICS®)
• WebSphere® MQ

Figure 1. SMP/E view of the system

Each system function is composed of one or more load modules. In a z/OS environment, a load module represents the basic unit of machine-readable, executable code. Load modules are created by combining one or more object modules and processing them with a link-edit utility. The link-editing of modules is a process that resolves external references and addresses. The functions on your system, therefore, are one or more object modules that have been combined and link-edited.

To see where the object module comes from, look at the example in Figure 2.

Figure 2. Load module creation

Most of the time, object modules are sent to you as part of a product. In this example, the object module MOD1 was sent as part of the product. Other times, you might need to assemble source code sent to you by product packagers to create the object module. You can modify the source code and then assemble it to produce an object module. In the example, SRCMOD2 is source code that you assemble to create object module MOD2. When assembled, you link-edit object module MOD2 with object module MOD1 to form the load module LMOD1.

In addition to object modules and source code, most products distribute many other parts, such as macros, help-panels, CLISTs and other z/OS library members. These modules, macros and other types of data and code are the basic building blocks of your system. All of these building blocks are called elements.

Elements are associated with, and depend upon, other products or services that may be installed on the same z/OS system. They describe the relationship the software has with other products or services that may be installed on the same z/OS system.