Other Parmlib Considerations

z/OS requires that parmlib reside on the system residence (SYSRES) volume if it is not cataloged.

It is important to learn how the parmlib is structured because it is one of the most important system libraries. Note the following:

The z/OS parameter library usually contains several dozen members. Each member has a unique format, and a different component of z/OS uses them.
Most parmlib member names are composed of a six‑character prefix followed by a two‑character suffix. The prefix is usually fixed according to the function of the member. The site can select the suffix. IBM‑supplied members have 00 as their suffix. For a list of parmlib members in the various z/OS architectures, see the Technical Reference.
Multiple versions of some parmlib members can exist by varying the member name suffix. This does not apply to all members.
Parmlib members can be grouped into general and specialized members. Each general member contains parameters and references to a number of specialized members.

One general member is designated as the master member, named IEASYS00. Parmlib is organized in an inverted tree structure with IEASYS00 at the top of the tree. z/OS always use the master member during IPL and can optionally use alternate general members that supplement IEASYS00.