Discontiguous Saved Segments Assign a name to segment and specify where it is to be stored on
disk. To do this, define an entry in the system name table (DMKSNTBL) with the NAMESYS macro.. See "Coding the NAMESYS Macro" in "Part 2. Defining Your VM/370 System." Or you can use the entries in
the DMKSNT module supplied with the starter system. Load and save the segment, using the appropriate EXEC procedure (CMSXGEN, DOSGEN, or VSAMGEN). Be sure that the proper linkage for attaching and detaching
di-scontiguous saved segments is in the operating s-ystemthat needs
the segment. CMS contains the linkage necessary to attach and detach
the discontiguous saved segments it supports.
Usually, the direct access storage space is allocated and the system
name table entries are created during system generation. You allocate DASD space as permanent (PERM) by executing the Format/Allocate program.
This program is executed during system generation, but it is a
standalone program that can be executed at any time. During system
generation, you designate the Cp-owned volumes by coding the SISOWN macro of the DMKSYS file. The system name table (DMKSNT) is also
created during system generation. If, at some time after system
generation, you wish to change the DMKSYS or DMKSNT files, you can do a
partial system generation and reassemble those files using the GENERATE EXEC procedure. GENERATE is described in "Part 5. Updating VM/370." You can load and save a discontiguous saved segment any time after
system generation. £Q1!§ideratiQ1!§.!Q!: Using ,ihe and By the time you complete the VM/370 system generation procedure, the CMS editor, EXEC, and OS simulation load modules exist on the CMS S-disk. Also, if you have followed VK/370 recommendations, you have created a
discontiguous saved segment, called CMSSEG, that contains the CMS editor, EXEC, and OS simulation routines (you save in Step 24). During virtual machine execution, CMS handles a call to the editor or EXEC processor as follows: CMS first searches for editor or EXEC load modules on all accessed CMS disks, except the S-disk. If you wanted to test changes made to the editor or EXEC processor, you could place the load modules on a disk other than the S-disk (that is available only to your virtual machine) and test
those changes. CMS next attempts to attach the shared segment. If you have not
reset the name of the shared segment by issuing a SET SYSNAME command, CMS attempts to attach the CMSSEG segment. If you wish to
use an alternate segment, indicate the alternate segment on a SET SYSNAME command and issue that command before the segment is
attached. If you do not want CMS to attach a shared segment when
editor, EXEC, or OS simulation routines are needed; issue a SET SISNAME command specifying as the segment name any name that does not
correspond to a named saved segment. Last, CMS attempts to load the appropriate modules from the CMS S-disk. Part 1. Planning for System Generation 83
Discontiguous Saved Segments handles a call for as simulation routines in a similar manner. first attempts to attach the named saved segment. Again, you can
indicate an alternate segment for loading or avoid loading a named saved
segment by specifying a nonexistent segment as the alternate. If a
named saved segment is not available, searches all accessed disks
for the as simulation load modules and loads them into high user storage
when they are found. The routines are kept in storage until CMS is
reloaded or until a SET SYSNAME command is issued for CMSSEG. Note that there is overhead associated with controlling saved
segments and ensuring their integrity. In small systems, the overhead
associated with using the CMSSEG saved segment may not be offset by the
benefits of sharing storage among users. Therefore, each must decide whether the use of CMSSEG is appropriate for its own
environment.
84 IBM Planning and System Generation Guide
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