z/VM: CP Commands and Utilities Reference - z/VM - IBM

If other pages in the segment were defined with the exclusive attribute (page
descriptor codes ER, EW and EN), any pages not specified on the command
line become exclusive read/write pages whose data is not saved. This
corresponds to page descriptor code EN.
The page number is a hexadecimal value less than or equal to X'7FEFF' (2047
MB). The following list shows examples of how hexadecimal storage addresses
translate into hexadecimal page numbers:
Storage Address
Page Number
00000xxx
0
00001xxx
1
00022xxx
22
00333xxx
333
04444xxx
4444
3E6FFxx
3E6FF
7F800xx
7F800
type
refers to the 2-character page descriptor code of the page range in the NSS. It
indicates the type of virtual machine access permitted to pages in the range.
The first character is either E for exclusive access or S for shared access.
Sharing of storage between virtual machines is based on 1 MB segments, so
that all 256 pages in any one segment must be either exclusive or shared.
The second character of the page descriptor code defines the storage
protection characteristics of the page. These character designators follow:
v R indicates that page protection is used to make the page range read-only.
v W means that the page is not protected, and users have read/write access.
v N stands for “read/write, no data saved,” meaning that the page is treated as
a new page when the user refers to it. The contents of, and storage keys for,
no-data-saved pages are not saved by the SAVESYS command.
v C stands for “CP-writable, virtual machine read-only, no data saved,”
meaning virtual machines have read-only access to these pages, but CP
services may change the data in the pages.
The contents of and storage keys for no-data-saved pages are not saved by the
SAVESYS command.
Valid page descriptor codes are:
DEFSYS
Code Meaning
EW Exclusive read/write access
EN Exclusive read/write access, no data saved
ER Exclusive read-only access
SW Shared read/write access
SN Shared read/write access, no data saved
SR Shared read-only access
SC CP-writable pages, shared read-only access by virtual machine, no data
saved
Chapter 2. CP Commands 213