The USERSECT CSECT defines space that is not used by CMS. A
modification or update to can use the 18 fullwords defined for USERSECT. There is a pointer (AUSER) in the NUCON area to the user
The DEVTAB CSECT is a table describing the devices available for the system. The table contains the following entries: 1 console 10 disks 1 reader 1 punch 1 printer 4 tapes You can change some existing entries in DEV1AB. Each device table
entry contains the following information: Virtual device address Device flags Device types Sy.bol name Address of the interrupt processing routine (for the console)
The virtual address of the console is defined at IPL time. The
virtual address of the user disks can be altered dynamically with the ACCESS command. The virtual address of the tapes can te altered in the
device table. Changing the virtual address of the reader, printer, or
punch will have no effect. Figure 26 describes the devices supported by Structure of eMS Storage
Figure 27 describes how CMS uses its virtual storage. The pointers
indicated (MAINSTRT, MAINHIGH, FREELOWE, and FREEUPPR) are all found in NUCON (the nucleus constant area). The sections of CMS storage have the following uses: 12 X'03000'). pointers, flags, and other data updated--by routines.
This area
the various
contains systell DMSFREE Free 12 ThIs--area-rs a free storage area, from which requests
from DMSFREE are allocated. The top part of this area contains the
file directory for the system Disk (SSTAT). If there is enough room
(as there will be in most cases), the FREE tAB table also occupies
this area, just below the SSTAT. Part 3. Conversational Monitor system (CMS) 241
Virtual Virtual , Symbolic
IBM Device Address
1 , Name Device Type 3210, 3215, 1052, ccu CON1 System console 3066, 3270 2314, 3330, 3340 190 DSKO System disk (read-only) 3350 "...,.4 .. 3330, 3340 191
DSK1 Primary disk (user files) 3350 2314, 2319, 3330, ccu DSK2 Disk (user files) 3340, 3350 ') 1/1 ').,10 .,.,.,n ccU DSK3 Disk (user files) £..J 1 ." JJJV, 3340, 3350 2314, 2319, 3330, 192 DSK4 Disk (user files) 3340, 3350 2314, 2319, 3330, ccu DSK5 Disk (user files) 3340, 3350 2314, 2319, 3330, ccu DSK6 Disk (user files) 3340, 3350 2314, 2319, 3330, ccu DSK7 Disk (user files) 3340, 3350 2314, 2319, 3330, 19E DSK8 Disk (user files) 3340, 3350 2314, 2319, 3330, ccu DSK9 Disk (user files) 3340, 3350 1403, 3203, 3211 OOE PRN1 Line printer
1443 2540, 2501, 3505 OOC RDR1 Card reader 2540, 3525 OOD PCH1 Card punch
2415, 2420, 3410, 181-4 TAP1-TAP4 Tape drives 3420 lThe device addresses shown are those that are preassembled into the CMS resident device table. These need only be modified and a new
device table made resident to change the addresses.
2The virtual device address (ccu) of a disk for user files can be
any valid System/370 device address, and can be specified by the CMS user when he activates a disk. If the user does not activate
a disk immediately after loading eMS, eMS automatically activates
the primary disk at virtual address 191.
Figure 26. Devices Supported by a CMS Virtual Machine , , I I I , , I , I Transient 12 Since it is not essentIal to keep all nucleus functions resident in storage all the
time, some of them are made "transient." This means that when they
are needed, they are loaded from the disk into the transient program
area. Such programs may not be longer than two because that
is the size of the transient area. (A page is 4096 bytes of virtual
storage.) All transient routines must be serially reusable since
they are not read in each time they are needed.
242 IBM VM/370 System programmer's Guide
Previous Page Next Page