When a problem with a software element is discovered, IBM® supplies its customers with a tested fix for that problem. This fix comes in the form of a program temporary fix (PTF). Although you may not have experienced the problem the PTF is intended to prevent, it is wise to install the PTF on your system. The PTF SYSMOD is used to install the PTF, thereby preventing the occurrence of that problem on your system.

Typically, PTFs are designed to replace or update one or more complete elements of a system function. Let's look at Figure 1.

Figure 1. Preventing problems with an element

In Figure 1, we see a previously installed load module, LMOD2. If we want to replace the element MOD1, we should install a PTF SYSMOD that contains the module MOD1. That PTF SYSMOD replaces the element in error with the corrected element. As part of the installation of the PTF SYSMOD, SMP/E relinks LMOD2 to include the new and corrected version of MOD1.

   ++PTF(PTF0001)              /* SYSMOD type and identifier.   */.
   ++VER(Z038) FMID(FUN0001)   /* Apply to this product.        */.
   ++MOD(MOD1)                 /* Replace this module           */
               DISTLIB(AOSFB)  /* in this distribution library. */.
   ...
   ... object code for module
   ...

PTF SYSMODs are always dependent upon the installation of a function SYSMOD. In some cases, some PTF SYSMODs may also be dependent upon the installation of other PTF SYSMODs. These dependencies are called prerequisites. We will look at a typical PTF prerequisite when we discuss the complexity of keeping track of the elements of the system.