format to CMS physical I/O requests. That is, CMS macros (such as
RDBUF/WRBUF, CARDRD/CARDPH, PRINTIO, and WAITRD/TYPLIN)
replace the CCW strings. If CMS/DOS is reading from DOS disks, I/O requests
are handled via the DIAGNOSE interface.
When an I/O operation completes, CMS/DOS posts the CCB or IORB with the
CMS return code. Partial RPS (rotational position sensing) support is available for I/O operations to CMS disks because CMS uses RPS in its channel programs.
However, RPS is not supported when real DOS disks are read. VSE Supervisor Control Blocks Simulated by CMS/DOS CMS/DOS supports VSE program development and execution for a single parti­
tion: the background partition. Because CMS/DOS does not support foreground
partitions, it also does not simulate the associated control blocks and fields for
foreground partitions. CMS/DOS does simulate the following VSE supervisor con­
trol blocks:
ABT AB--Abnormal Termination Option Table
BBOX--Boundary Box
BGCOM--Background Partition Communication Region
EXCPW--Work area for module DMSXCP
FICL--First in Class
LUB--Logical Unit Block
NICL--Next in Class PCT AB--Program Check Option Table
PIBTAB--Program Information Table
PIB2TAB--Program Information Block Table Extension PUB--Physical Unit Block PUBOWNER--Physical Unit Block Ownership Table
SYSCOM--System Communication Region
TCB--Task Control Block LOCT AB--LOCK/UNLOCK Resource Table
DIB--Disk Information Block
For detailed descriptions of CMS/DOS control blocks, refer to the VAI/ SP Data
Areas and Control B lock Logic, Volume 2.
User Considerations and Responsibilities
A critical design assumption of CMS/DOS is that installations that use CMS/DOS for VSE program development also use and have available a VSE system. There­
fore, if you want to use CMS/DOS for VSE program development, you should
order and install a VSE system. Also, if you want to use the DOS/VS COBOL and DOS PL/I Optimizing compilers under CMS/DOS, you must order them and
install them on your VSE system.
You should consider several other facts if you plan to use CMS/DOS. The follow­
ing sections describe some of the user considerations and responsibilities. VSE System Generation and Updating Considerations
The CMS/DOS support in CMS may use a real VSE system pack. CMS/DOS provides the necessary path and then fetches VSE logical transients and system
routines directly as well as the DOS/VS COBOL and DOS PL/I Optimizing com-
. pilers directly from the VSE system or private core image libraries. VSE Support Under eMS 411

VM/SP Directory Entries
It is your responsibility to order a VSE system and then generate it. Also, if you
plan to use DOS compilers, you must order the current level of the DOS/VS COBOL compiler and DOS PL/I Optimizing compiler and install them on the
same VSE system.
When you install the compilers on the VSE system, you must link-edit all the com­
piler modules as relocatable phases using the following linkage editor control
statement: ACTION REL
You can place the link-edited phases in either the system or the private core image
library.
When you later invoke the compilers from CMS/DOS, the library (system or pri­
vate) containing the compiler phases must be identified to CMS. You identify all
the system libraries to CMS by coding the filemode letter that corresponds to that
VSE system disk on the SET DOS ON command when you invoke the CMS/DOS environment. You identify a private library by coding ASSGN and DLBL com­
mands that describe it. The VSE system and private disks must be linked to your
virtual machine and accessed before you issue the commands to identify them for
CMS. CMS/DOS has no effect on the update procedures for VSE, COBOL, or DOS PL/I. Normal update procedures for applying IBM-distributed coding changes
apply.
For detailed information on how to generate VM/SP with CMS/DOS, refer to the
publication VM / SP Planning Guide and Reference and the VM / SP Installation
Guide.
The VSE system and private libraries are accessed in read-only mode under CMS/DOS. If more than one CMS virtual machine is using the CMS/DOS envi­
ronments you should update the VM/SP directory entries so that the VSE system
residence volume and the VSE private libraries are shared by all the CMS/DOS users.
The VM/SP directory entryfor one of the CMS virtual machines should contain
the MDISK statements defining the VSE volumes. The VM/SP directory entries
for the other CMS/DOS users should contain LINK statements.
For example, assume the VSE system libraries are on cylinders 0 through 149 of a 3330 volume labeled DOSRES. And, assume the VSE private libraries are on cyl­
inders 0 through 99 of a 2314 volume labeled DOSPRI. Then, one CMS machine
(for example, DOSUSER1) would have the MDISK statements in its directory
entry. USER DOSUSER1 password 320K 2M G
MDISK 331 3330 0 150 DOSRES R rpass MDISK 231 2314 0 100 DOSPRI R rpass
All the other CMS/DOS users would have links to these disks. For example
412 VM/SP System Programmer's Guide