DD Statement

Following almost every EXEC PGM statement are one or more DD statements. Each DD statement defines a data set that may be accessed by the job step’s program. The Tachyon Operating System supports instream data sets (DD *), spooled output data sets (DD SYSOUT), null data sets (DD DUMMY) and disk data sets.

The DD statement parameters are dependent on how the data sets are accessed. This release of the Tachyon Operating System supports the BSAM and QSAM access methods and the BPAM and VSAM access methods for input. For this reason, some of the DD statement parameters related to other access methods are not supported.

For "normal" data sets (those that are not instream, SYSOUT or DUMMY), the Tachyon Operating System acts as if DFSMS/MVS is in control and as if the ACS rules modify all data sets to be on disk instead of tape. These "rules" also provide defaults for missing parameter values such as SPACE.

Another differences arises because disk data sets must be mapped to local workstation files by the Tachyon Operating System. In fact, workstation files are far more similar to z/OS UNIX files than they are to other data set types. For instance, there is no VTOC for your local files that would contain data set attributes such as RECFM and LRECL. This means that these attributes must be supplied on every DD statement unless they are supplied through the DSNMAPxx.ini DSATTR or DSNMAP configuration file statements.

DD Statement Parameters

The following DD parameters are processed and their values stored in various control blocks: BFALN, BFTEK, BLKSIZE, BUFL, BUFNO, BUFOFF, CHARS, DCB, DIAGNS, DISP, DSNAME, DSNTYPE, DSORG, DUMMY, EROPT, FCB, FILEDATA, FREE, KEYLEN, KEYOFF, LRECL, NCP, OPTCD, PATH, PATHDISP, PATHMODE, PATHOPTS, PRTSP, RECFM, RKP, SYSOUT, STACK and UCS.

The following DD parameters are checked for syntax but otherwise ignored: ACCODE, AVGREC, BURST, CCSID, CHKPT, COPIES, DATACLAS, DEN, DEST, DYNAM, EXPDT, FASH, HOLD, LIKE, MGMTCLAS, MODIFY, OUTLIM, PROTECT, REFDD, SEGMENT, SPACE, SPIN, STORCLAS, TRTCH and UNIT.

The DD *, DATA and DLM parameters are used to create instream data sets.

The following DD parameters are not supported by this release of the Tachyon Operating System: AMP, BFTEK=D, BFTEK=E, BUFIN, BUFMAX, BUFOUT, BUFSIZE, CNTL, CPRI, CYLOFL, DCB=dsn, DDNAME, DSID, DSORG=CX, DSORG=DA, DSORG=GS, DSORG=IS, DSNTYPE, EROPT=T, FUNC, GNCP, INTVL, IPLTXID, LABEL, LIMCT, MODE, MSVGP, NTM, OPTCD=ILMRY, OUTPUT, PCI, QNAME, RECORG, RESERVE, RLS, SECMODEL, SUBSYS, THRESH and VOLUME.

The following DD parameters are treated differently by the Tachyon Operating System than by z/OS:

DD Name

This release of the Tachyon Operating System permits the specification of concatenated sequential data sets but it does not switch data sets after the first one has been read.

DSNAME

Except for temporary data set names, all data set names must consist of names separated by periods. Each name must be from one to eight digits or upper case letters and the first character of each name must be a letter. Data set names may not be within quotes. Temporary data set names must begin with two ampersands (e.g. &&TEMPDSN). For partitioned data sets, the member name field is allowed. Because generation data groups (GDGs) are not supported, the relative generation number is not allowed. Because ISAM is not supported, the data set area field is not allowed.

For sequential disk data sets, the DSNAME parameter may be specified with the PATH parameter. The DSNAME parameter value is stored in control blocks and printed in messages but it has no other use. Except for temporary data sets, the PATH parameter must be specified for sequential disk data sets so that the Tachyon Operating System knows which workstation file is to be accessed.

For partitioned data sets, the PATH parameter is not allowed and the path information must be obtained via the DSNMAPxx.ini DSNMAP configuration file statements.

For VSAM data sets, only the DSNAME and DISP parameters are needed. The DSNAME parameter must specify the name of a predefined VSAM file that is in one of the directories specified in a DSNMAPxx.ini CATALOG configuration file statement. Because the Tachyon Operating System does not support JCL definition and deletion of VSAM files, only DISP=SHR or DISP=OLD should be used and DISP=NEW and DISP=(,DELETE) should not be specified. This release of the Tachyon Operating System does not support the AMP parameter of the DD statement. You must specify the number of strings and buffers (STRNO, BUFND, BUFNI and BUFSP) in the ACB.

For temporary data sets, the generated data set name is: SYSyyddd.Thhmmss.JOBjobno.jobname.dsname, where dsname is either the &&dsname specified or the generated dsname of &&Rseqno. Temporary data sets are stored in the temporary directory with a file name matching the data set name and a file name extension of ".tmp".

The generated data set names for instream data sets are: JOBjobno.jobname.stepname.Iseqno. The generated data set names for SYSOUT data sets are: JOBjobno.jobname.stepname.ddname. Both instream and SYSOUT data sets are stored in the spool directory. Instream data sets are deleted as each step completes. The file name of SYSOUT data sets is the data set name with a file name extension of ".lst".

FILEDATA

The Tachyon Operating System supports the FILEDATA parameter for all sequential and partitioned data sets, even those with a DSNAME. The FILEDATA parameter value may be one of: TEXT, BINARY or RECORD. FILEDATA=TEXT specifies that the data in the file contains ASCII text lines delimited with carriage return and/or new-line characters. FILEDATA=BINARY specifies that the file contains raw binary data that is not to be converted and that it contains no record delimiters. FILEDATA=RECORD specifies that the file contains EBCDIC data and that in the case of RECFM=U or RECFM=V, it contains record descriptor prefixes.

If FILEDATA is not specified for a sequential disk data set and not provided via the DSNMAPxx.ini DSATTR or DSNMAP configuration file statements, the default is FILEDATA=RECORD for temporary data sets and FILEDATA=TEXT for all others. For a simulated partitioned data set, FILEDATA must be specified via the DSNMAPxx.ini configuration file statements.

FREE

This release of the Tachyon Operating System permits the specification of FREE=CLOSE but it does not deallocate data sets as they are closed.

PATH

The PATH parameter is allowed with the DSNAME parameter for sequential disk data sets. In fact, it is required for all non-temporary sequential disk data sets unless it is provided via the DSNMAPxx.ini DSNMAP configuration file statements. However, for partitioned and VSAM data sets the PATH parameter is not allowed and the path information must be obtained via the DSNMAPxx.ini DSNMAP or CATALOG configuration file statements.

When DSNAME is specified for a non-temporary disk data set, the data set is treated as a normal z/OS data set and the UNIX file-related parameters such as PATHDISP, PATHMODE and PATHOPTS are not allowed. If DSNAME is not specified for a non-temporary disk data set, the data set is treated as a UNIX file.

The PATH parameter value must be the path name of a workstation file. It may be surrounded by quotes and it must not contain blanks or quotes. The special path name /dev/null is recognized as a "dummy" UNIX file.

RECFM

When FILEDATA=RECORD is specified, the RECFM parameter defines the format of the file data. RECFM=F and RECFM=FB files are written without record delimiters. RECFM=U records are written with a 2-byte prefix containing the length of the record exclusive of the prefix. RECFM=V, VB, VS and VBS records are written with a 4-byte IBM-standard Record Descriptor Word (RDW). RECFM=VB and VBS blocks also contain a 4-byte IBM-standard Block Descriptor Word (BDW). RECFM=V and VS records are not prefixed by a BDW, instead the Tachyon Operating System generates a BDW as each record is read. RECFM=D is not supported.

For FILEDATA=TEXT or FILEDATA=BINARY file, the RECFM parameter causes the Tachyon Operating System to accept output records or return input records in the specified format. However, the data file will either contain no record separators in the case of FILEDATA=BINARY or will contain ASCII text line with normal line-end characters in the case of FILEDATA=TEXT.

For SYSOUT data sets, the spool files are always written as if FILEDATA=TEXT,RECFM=UA had been specified. However, the actual RECFM specified on the DD statement or in the DCB should match the program’s record format. The Tachyon Operating System automatically converts the program’s records to the spool file format. FILEDATA is not a valid parameter for SYSOUT data sets.

Example DD statement

//MYDD DD DSN=MY.DATA.SET,DISP=(NEW,CATLG,DELETE),
// DSORG=PS,RECFM=VBA,LRECL=125,BLKSIZE=6000,
// PATH='C:\myfiles\my.test.data.vba',FILEDATA=RECORD