Page of GC20-1807-7 As Updated April 1, 1981 by TNL GN25-0829 SYNADAF-SVC68 SYNADRLS-SVC68 BSP-S VC6 9 TGET/TPrJT­ SVC93 TCLEARQ-SVC94 STAX-SVC96 NOTE POINT CHECK
DCB BFALN BLKSIZE BUFCB BUFL BUFNO DDNAME DSORG EODAD EXLST KEYLENl LIMCT
LRECL
MACRF OPTCD RECFM SYNAD NCP --------------
data control block specified. CMSCBs are created by
FILEDEF commands.
All the options of SYNADAF are supported. SYNADAF analyzes an I/O error and creates an error message in
a work buffer.
All the options of SYNADRLS are supported. SYNADRLS frees the work area acquired by SYNAD and deletes the
work area from the save area chain.
All the options of BSP are supported. BSP decrements
the item pointer by one block.
TGET and TPUT operate as if EDIT and WAIT were coded.
TGET reads a terminal line. TPUT writes a terminal
line.
TCLEARQ in CMS clears the input terminal queue and
returns control to the user. Updates a queue of CMTAXEs each of which defines an
attention exit level.
All the options of NOTE the relative position
written ..
are supported. NOTE returns
of the last block read or
All the options of POINT are supported. POINT causes
the control program to start processing the next read
or write operation at the specified item number. The
TTR field in the block address is used as an item
number.
All the options of CHECK are supported.
the I/O operation for errors and
condi t ions.
The following fields of a DCB may
relative to .... ,... particular access method '-'l.le be
CHECK tests
exceptional
specified,
indicated: lm!!1 BPAM F,D F,D F,D F,D
n(number) n n n
a (address) a a a
n n n n
n n n n
s (symbol) s s s
DA PO PS PS a a a
a a a a
n n
n
n n n R,W R,W R, W, P G,P,L,M A£' E, F, R F,V,a F,V,U F,V,B,S,A,M,U F,V,B,U,A,M,S a a a a
n n
lIf an input data set is not a EDAM data set, zero is the only value that
should be specified for KEYLEN. This applies to the user exit lists as
well as to the DCB macro instruction. Part 3. Conversational Monitor System (CMS) 277

April 1, 1981 ACCESS METHOD SUPPORT The manipulation of data is governed by an access method. To facilitate
the execution of OS Code under eMS, the processing program must see data
as OS would present it. For instance, when the processors expect an
access method to acquire input source cards sequentially, CMS invokes specially written routines that simulate the OS sequential access method and pass data to the processors in the format that the OS access methods
would have produced. Therefore, data appears in storage as if it had
been manipulated using an OS access method. For example, block
descriptor words (BOW), buffer pool management, and variable records are
updated in storage as if an OS access method had processed the data.
The actual writinq to and reading from the I/O device is handled by CMS file manaqement. Note that the character string X'61FFFF61' is by eMS as an end of file indicator.
The essential work of the volume table of contents (VTOe) and the
data set control block (OSCB) is done in eMS by a master file directory (MFO) which updates the disk contents, and a file status table (FST) (one for each data file). All disks are formatted in physical blocks of 800 bytes. eMS continues to update the OS format, within its own format, on the device, for files whose number is 4. That is, the
block and record descriptor words (BOW and ROW) are written along with
the data. If a data set consists of blocked records, the data is
written to, and read from, the I/O device in physical blocks, rather
than loqical records. eMS also simulates the specific methods of
manipulating data sets.
To accomplish this simulation, CMS supports certain essential macros
for the following access methods: • BDAM • BPAM • BSAM/QSAM • VSAM (direct) --identifying a record by a key or by its
relative position within the data set.
(partitioned) --seeking a named member within data set.
(sequential) --accessing a record in a sequence in
relation to preceding or following records.
(direct or sequential) --accessing a record sequentially
or directly by key or address. CMS support of OS VSAM files is based on DOS/VS Access Method Services and Virtual Storage Access Method (VSAM). Therefore, the OS user is restricted to those
functions available under "DOS/VS Access Method Services." See the section "eMS Support for as and DOS VSAM Functions" for details. CMS also updates those portions of the OS control blocks that are
needed by the as simulation routines to support a program durinq
execution. Most of the simulated supervisory OS control blocks are
contained in the following two eMS control blocks: CMSCVT simulates the communication vector table. Location 16 contains
the address of the CVT control section.
278 IBM VM/370 System Programmer's Guide