SYSCYL=nnn is the real starting cylinder of the virtual disk (specified
by VSYSRES and VSYSADR) that is the system residence volume for the system to be saved. This operand is ignored if VSYSADR=IGNORE. SYSSTRT= (cc, p)
designates the starting cylinder (cc) and paqe address (p) on SYSVOL at which this named system is to be saved. During- the
processing of the SAVE and LOAD commands, this is used to
generate the "cylinder page and device" address for the DASD operations. These numbers are specified in decimal.
The number of pages written to this area is the total number
specified via the SYSPGNM operand, plus one information page. SYSPGCT=pppp is the total number of pages (pppp) you specify to be saved
(that is, the total number of pages you indicate via the SYSPGNM operand). This is a decimal number, up to four
digits. The number of pages specified does not have to be a
multiple of the number of pages in a segment, but can be some portion of a segment(s). SYSPGNM=(nn,nn,nn-nn, ••• )
are the numbers of the pages to be saved. Pages may be
specified singly or in groups. For example: if pages 0, 4, and 10 through 13 are to be saved, use the format: SYSPGNM:(0,4,10-13). SYSHRSG=(S,S, ••• ) PROTECT are the segment numbers designated as shared. The pages in
these segments are set up at load time to be used by any user
loading by this name. All segments to be shared must be
reenterable.
= specifies whether CP default value is ON. OFF. is
To
to protect shared segments. The
turn off segment protection, specify !Qte: For each shared segment specified, 64K of virtual storage is
reserved. The number of pages actually saved (via the SAVESYS command)
can be less than a segment. However, only one saved system name can be
associated with each 64K request. LOADING AND SAVING DISCONTIGUOUS SHARED SEGMENTS Before a discontiguous saved segment can be attached and detached by
name, it must be loaded and saved. The discontiguous saved segment must
be loaded at an address that is beyond the highest address of any virtual machine to which it will be attached. It is the system
programmer's responsibility to make sure the name segment is loaded at
an address that does not overlay the defined virtual machine or any
other named segment that may be attached at the same time.
138 IBM VM/370 System Guide

April 1, 1981
The load address for the discontiguous saved segment should be just
beyond the largest virtual machine that uses it. If the load address is
unnecessarily high, real storage is wasted because CP must have segment
table entries for storage that is neVer used. For example, assume you have five CMS virtual machines in your
installation. Also assume that all five use the CMS support for DOS program development and testing which is in a 32K segment named CHSDOS. If each of your five CMS virtual machines has a machine size of 320K you
should load the CMSDOS segment just beyond 320K. If you load CMSDOS at
a much higher address, for example 512K, you are wasting real storage.
In this case, whenever one of your CMS virtual machines attaches the CMSDOS segment, CP creates segment table entries for a 544K (512K + 32K)
virtual machine. Although the virtual machine cannot refer to storage
addresses beyond 320K or below 512K, CP still must have segment table
entries in nonpageable real storage for those virtual addresses. Once the named segment is loaded at the correct address, you can save
it by issuing the CP SAVESYS command. To be sure that the CMS discontiguous saved segment has segment protection, set the storage key
for the seqment, via the CMS SETKEY command: to something other than X'F' before you save it.
The format of the eMS SETKEY command is: r ----------------------------------------------------------------------, SETKEY I key systemname [startadr] I key I is the storage protection key, specified in decimal. The
valid keys are 0-15. systemname is the name of the saved system or segment for which the
storage protection is being assigned.
startadr is the starting address (in hexadecimal) at which the keys
are to be assigned. The address must be within the address
range defined for the saved system or discontiguous saved
segments. Using the startadr operand, you can issue the SETKEY command several times and, thus, assign different
keys to various portions of the saved system or HOW THE INTERFACE WORKS The linkage to attach and detach discontiguous saved segments is
supported via several CP DIAGNOSE codes. Since the virtual machine is responsible for insuring that the
discontiguous saved seqment it is attaching does not overlay other
programming code, it must know how much virtual storage it has. By X'EO' during its initialization process, the 'virtual machine can determine its virtual machine storage size.
When the virtual machine needs to attach a discontiguous saved
segment, it must first ensure that the segment is available and that it
does not overlay existinq storage. By issuing the DIAGNOSE code X'64' Part 2. Control Proqram (CP) 139