eMS Support for OS and VSE/VSAM Functions
CMS supports interactive program development for OS and VSE programs using
VSAM. CMS supports VSAM macros for OS and VSE programs. The complete
set of VSE/VSAM macros and options and a subset of OS/VSAM macros are
supporte.d.
CMS also supports Access Method Services to manipulate OS and VSE VSAM and
SAM data sets.
Under CMS, VSAM data sets can span up to 10 volumes. CMS does not support
VSAM data set sharing; however, CMS already supports the sharing of minidisks
or full pack minidisks.
VSAM data sets created in CMS are not in the CMS file format. Therefore, CMS
commands used to manipulate CMS files cannot be used for VSAM data
sets that are read or written in CMS. A VSAM data set created in CMS (using
VSE/VSAM) has a file format that is compatible with OS VSAM data sets as long
as the physical record size of the data set is .5K, lK, 2K, or 4K. For complete
information on OS/VS VSAM and VSE/VSAM data set compatibility, see the
VSE/VSAM General Information Manual.
Because VSAM data sets in CMS are not a part of the CMS file system, CMS file
size, record length, and minidisk size restrictions do not apply. The VSAM data
sets are manipulated with Access Method Services programs executed under CMS,
instead of with the CMS file system commands. Also, all VSAM minidisks and full
packs used in CMS must be initialized with the Device Support Facility; the CMS FORMAT command must not be used.
CMS supports VSAM control blocks with the GENCB, MODCB, TESTCB, and SHOWCB macros.
In its support of VSAM data sets, CMS uses RPS (rotational position sensing)
wherever possible. CMS does not use RPS for 2314/2319 devices, or for 3340 devices that do not have the feature.
Hardware Devices Supported
CMS support of VSAM data sets is based on VSE/VSAM. Except for the 3380, only disks supported by VSE can be used for VSAM data sets in CMS. These
disks are: I · IBM 2314 Direct Access Storage Facility
IBM 2319 Disk Storage
IBM 3310 Direct Access Storage
IBM 3330 Disk Storage, Models 1 and 2
IBM 3330 Disk Storage, Model 11
IBM 3340 Direct Access Storage Facility
IBM 3344 Direct Access Storage
IBM 3350 Direct Access Storage
IBM 3370 Direct Access Storage
IBM 3375 Direct Access Storage
IBM 3380 Direct Access Storage (OS/VSAM environment of CMS only). eMS Support for as and VSE/VSAM Functions 415

CMS disk files used as input to or output from Access Method Services may reside
on any disk supported by CMS. VSE Supervisor Macros and Logical Transients Support for VSAM CMS supports VSAM for as and VSE users. However, the CMS support of
VSAM is based on VSE/VSAM. VSE supervisor macros required by VSE/VSAM
are supported by CMS. See Figure 45 on page 392 for a complete list of supervisor
macros supported.
CMS distributes the VSE transients that are needed in the VSAM support. Thus,
as users do not need to have the VSE system pack online when they are compiling
and executing VSAM programs.
CMS uses all of the VSE B-transients except those that build and release extent
blocks. The extent block is not supported in CMS and, thus, neither are the
B-transients that control extent blocks.
The CMSDOS shared segment contains the B-transients that are simulated for VSE
support in CMS. The B-transients that pertain only to VSAM are included in the
VSAM saved segment. Other VSE routines required by VSE/VSAM are con­
tained in the CMSBAM shared segment. This includes the common VTOC han­
dler routines, SAM data management, and the VSAM look-aside function.
Data Set Compatibility Considerations
CMS can read and update VSAM data sets that were created under VSE or OS/VS. In addition, VSAM data sets created under CMS can be read and updated
by VSE or OS/VS as long as the physical record size of the data set is .5K, lK,
2K, or 4K.
However, if you perform allocation on a minidisk in CMS, you cannot use that
minidisk in an as virtual machine in any manner that causes further allocation.
VSE/VSAM (and, thus, CMS) ignores the format-5, free space, DSCB, on VSAM
disks when it allocates extents. If allocation later occurs in an as machine, as
attempts to create a format-5 DSCB. However, the format-5 DSCB created by as
does not correctly reflect the free space on the minidisk. In CMS, allocation occurs
whenever data spaces or unique data sets are defined. Space is released whenever
data spaces, catalogs, and unique data spaces are deleted.
For complete information on OS/VS VSAM and VSE/VSAM data set compatibili­
ty, see the VSE/VSAM General Information.
ISAM Interface Program (lIP)
CMS does not support the VSAM ISAM Interface Program (lIP). Thus, any pro­
gram that creates and accesses ISAM (indexed sequential access method) data sets
cannot be used to access VSAM key sequential data sets. There is one exception
to this restriction. If you have (1) as PL/I programs that have files declared as
ENV(INDEXED) and (2) if the library routines detect that the data set being
accessed is a VSAM data set, your programs will execute VSAM I/O requests.
416 VM/SP System Programmer's Guide