Understanding the System Execution Space and CP Customization Methods

Before we can discuss how to dynamically add code to CP, you need to understand the layout of the address space in which CP executes. This address space is called the system execution space (SXS). Also, we need to compare the SYSGEN method of customizing CP (the old way) with the dynamic method of customizing CP (CP Exits).

While explaining the layout of the SXS and the two methods of customizing CP, we will use a simple example for the CP nucleus area of the SXS and the dynamic area of the SXS. In this example, we will ignore the following:
  • Other parts of the SXS located above the dynamic area
  • HSA (hardware system area)
  • Other miscellaneous areas that are not relevant to our discussion

Figure 1 and Figure 1 show the CP nucleus at the bottom of the picture and the SXS dynamic area at the top. The SXS dynamic area is used for all of CP's dynamic storage requirements: CP control blocks, paging, and so forth.