Although this subject is somewhat out of the scope of the course, we hope that you did not have problems to discover that the HELP segment is defined as physical segment HELPINST. The command Query Segment gives you a list of the currently active segments in your virtual machine. The name of the segments may however differ from system to system, therefore you should have looked at the SYSTEM SEGID file that you can find on the S-disk. This file defines the relation between the physical and logical segments.
In summary, remember this about the shared segment organizations:
VM/SP (and VM/ESA 370 Feature)
| Physical Segment | Made by CP by exploiting the 370 architecture, where the size of a segment is 64K. Such a physical segment contains just one big block of coding and is activated by a little Assembler program that loads the segment(s) and branches to its start address. |
| Logical Segment | A CMS construct: CMS allows a system programmer to place CMS objects in a logical segment. A logical segment is defined in a physical segment. Logical segments were introduced in VM/SP Release 6. Objects that can be stored in logical segments are : EXECs, MODULEs, Message repositories, Minidisk directories, CSL routines |
VM/ESA
| Physical Segment | Same as above, but here the 370/XA architecture forces that the size of a segment is 1 Meg. |
| Logical Segment | Same as above. CMS is the only to see objects in a logical segment. |
| Segment Member |
A CP construct: CP allows a
physical segment to be subdivided in members ;
a physical segment with
members is then called a Segment Space.
This allows for example to place SQL and ISPF in same segment of
1 Megabyte.
CMS sees almost no difference between an ordinary physical segment and a member. |
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