Physical and Logical Saved Segments

A saved segment is an area of virtual storage that is assigned a name, loaded with data or programs, then saved in a system data file in spool space. Using saved segments is a way of using storage that is not yours.

Segment spaces, member saved segments, and discontiguous saved segments (DCSSs) reside on CP-owned volumes and must be defined to CP before being used. A segment space, which begins and ends on a megabyte boundary, contains one or more member saved segments, which begin and end on page boundaries. A DCSS also begins and ends on a megabyte boundary, but does not contain members.

Defining frequently used data or programs as saved segments provides several advantages:
  • Several users can access the same saved segment, which helps you use real storage more efficiently.
  • Saved segments need not be in the address range of a virtual machine (this can also help you use storage more efficiently).
  • Space for saved segments can be reserved within a virtual machine's address space, which helps you make sure that the saved segment is always available.
A physical saved segment is a member saved segment or DCSS that may contain one or more logical saved segments that CMS recognizes. Defining logical saved segments provides further advantages:
  • Each logical saved segment can contain different types of program objects, such as modules, text files, execs, callable services libraries, language information, and user-defined objects, or a single minidisk file directory. You can use logical saved segments to package your entire application. For example, you may want to create a logical segment definition file that defines the parts of your application. You could then send it to the system administrator, who will create the logical saved segment and make it available for other to use.
  • You can use physical saved segments more efficiently by defining many different logical saved segments in a single physical saved segment.
  • Users can access specific logical saved segments rather than all the contents of a physical saved segment.

For information about defining saved segments, see z/VM: CP Planning and Administration.