Initializing a Named or Saved Systems
A named system is a copy of the nucleus that has been saved and naaed with the CP SAVESYS co •• and. It is faster to IPL a na.ed syste. than to
IPL by disk address because CP maintains the named system in page for.at
instead of CMS disk for.at. That is, the saved system is on disk in 4096-byte blocks instead of 800-byte blocks. The initialization of a
saved system is also faster because the SSTAT is already built.
The shared system is a variant of the saved system. In the shared
system, reentrant portions of the nucleus are placed in storage pages
that are available to all users of the shared system. Each user has his own copy of nonreentrant portions of the nucleus. The shared pages are
protected by CP, and may not be altered by any virtual machine.
During DMSINI processing, the virtual machine operator
the nucleus must be written (via message DMSINI607R) • If
answers no, control passes directly to DMSINS to initialize
saved system specified by the operator in his answer DMSINI606R. is asked if
the operator
the nailed or
to aessage Handling the First Command Line Passed to CMS DMSINT, the CMS console manager, contains the code to handle commands stacked by module DMSINS during initialization processing. DMSINT checks for the presence of a stacked command line, and if there is one
to process, processes it just as it would a ccmmand entered during a
terminal session. That is, DMSINT calls the iAITREAD subroutine and
issues an SVC 202 to execute the command. When first command processing
completes, DMSINT receives control to handle co •• ands entered at the
console for the duration of the session.
Setting and Querying Virtual Machine Environment Options DMSSET sets up
the publication
these settings
structured and DMSSET. the virtual .achine environment options, as outlined in ££!!sng DMSQRY displays
at the user console. Both of these modules are
relatively easy to follow, except for so.e sections of DMSSET: SET DOS ON (VSAM) PROCESSING DMSSET ----(label DOS) If a disk mode is specified on the command line, ensure
that it is valid. DMSLAD ---rf-the disk mode specified is valid, locates and returns the address
of the disk. Issues DIAGNOSE 64 FINDSYS to locate the CMSDOS segment. If the
segment is not already loaded, issues DIAGNOSE 64 LOADSYS to load it. 2-60 IBM VM/370 System Logic and Program Determination--Voluae 2

Sets up the $$B-transient area for use by DOS routines. DftSSET ----If-SET DOS OFF has been specified, issues the DI1GNOSE 64 PURGESYS function for the CftSDOS segment and, if VSlft has been loaded, for the segment. DftSSET: SET SYSNAftE PROCESSING Determines whether the name of the CftSSEG segment is being changed. DftSSET ---netermines whether NONSBARE is specified. If so, the segment may be
loaded and kept. If NONSBARE is not specified, the segment is purged,
because it is needed only on demand. Once a new name is placed in the SYSNAftES table replacing CftSSEG, the DIAGNOSE 64 FINDSYS function is issued to determine whether the new name has been entered correctly. If the FINDSYS is successful, the
size of the virtual machine is compared to beginning address of the
segment to determine whether the segment overlays virtual machine storage. D"SSET ---rf-the segment can be used (i.e. does not overlay the virtual machine storage) the DIAGNOSE 64 LOADSYS function is performed. If the LOADSYS executes successfully, control passes to D!SINT, where the
segment is purged (because it is only needed on demand). CMS Method of operation and Program Organization 2-61