Data File Types

Programs run by the Tachyon Operating System can access sequential files, simulated partitioned data sets, SYSOUT files, VSAM files and UNIX files. Sequential and UNIX files can be read, written and updated. Simulated partitioned data sets and VSAM files can be read and SYSOUT files can be written.

Sequential Files

Sequential files can be in one of three major formats. These formats are indicated through the FILEDATA parameter of the DD statement or the DSNMAPxx.ini DSATTR or DSNMAP configuration file statements.

Text Files

Text files are indicated via the FILEDATA=TEXT parameter. This is the default for sequential files. When read, each text line may be terminated by a carriage return, a line feed or both. When read via a DCB with RECFM=F or FB, the records are padded with blanks out to the logical record length. When written, each line is stripped of ending white space. Text files may not be updated and may not be accessed via a DCB with RECFM=VS or VBS.

Binary Files

Binary files are indicated via the FILEDATA=BINARY parameter. Data in binary files does not contain record separators and it is not translated when it is read or written. On input, the maximum number of bytes up to the logical record length are read. For RECFM=V or VB, an RDW is created. For RECFM=F or FB, the file size must be a multiple of the logical record length. On output, each logical record is written to the file. Binary files may not be accessed via a DCB with RECFM=VS or VBS.

Record Files

Record files are indicated via the FILEDATA=RECORD parameter. These files are very similar in format to mainframe data sets. RECFM=F or FB files do not contain record or block length indicators. These files may be read or written using any block size which is a multiple of the record size. RECFM=U records contain a 2-byte record prefix that does not include the prefix length. RECFM=V and VS records contain an IBM-standard Record Descriptor Word (RDW). However, RECFM=V and VS files do not contain a Block Descriptor Word (BDW). RECFM=VB and VBS files contain both BDWs and RDWs.

Partitioned Data Sets

Partitioned data sets are collections of sequential files. On the workstation, these collections are organized in directories. The Tachyon Operating System simulates many aspects of partitioned data sets using files within workstation directories.

Files within a simulated partitioned data set are selected by the Tachyon Operating System using the PATH parameter of the DSNMAPxx.ini DSNMAP configuration file statement. For a partitioned data set, the PATH parameter is a pattern used to match files in a directory.

For example, if the directory C:\PDS contains the following files:

then for the DSNMAP statement:

the simulated partitioned data set MY.PDS would appear to contain members AAAAAAAA and CCCC.

Just as for sequential files, the FILEDATA parameter sets the file format of the members of a partitioned data set. For a simulated partitioned data set the FILEDATA parameter must be specified using the DSATTR or DSNMAP statements of the DSNMAPxx.ini configuration file. FILEDATA(BINDER) may be used to define a simulated load library. Simulated load libraries are set for execute-only and may not be read or updated.

Members of a partitioned data set can be read using BSAM or QSAM if the member name is specified with the DSNAME parameter of the DD statement. The simulated directory of a partitioned data set can be read using BSAM or QSAM if no member name is specified and the DCB RECFM is F or U and the BLKSIZE is 256.

The Tachyon Operating System also supports input mode for the BPAM access method. Only the BLDL, CHECK, CLOSE, DEBCHK, FIND, LINK(X), LOAD, NOTE, OPEN, POINT, READ, RDJFCB and XCTL(X) services are supported for a BPAM DCB. The LINK(X), LOAD and XCTL(X) services require FILEDATA(BINDER). CHECK, FIND, NOTE, POINT and READ are not allowed for FILEDATA(BINDER) data sets.


SYSOUT files are stored in the directory set by the DSNMAPxx.ini SPOOL parameter. SYSOUT files are written as ASCII text files with ASA control characters. Any table reference characters (OPTCD=J) are removed. This release of the Tachyon Operating System replaces machine control characters with a blank ASA control character. SYSOUT files may not be written via a DCB with RECFM=VS or VBS.

VSAM Files

VSAM files appear as multiple workstation files. One file contains the VSAM file’s attributes, which on the mainframe are stored in the catalog. Additional workstation files contain the VSAM file’s data. There is one workstation file for each VSAM file component. For ESDS and RRDS files there is only the data component file. For KSDS and VRRDS files there is both a data and an index component file.

The Tachyon Operating System locates VSAM files by searching the directories listed in the DSNMAPxx.ini CATALOG configuration file statement. The catalog information files are named with the VSAM cluster name followed by “.CAT”. The component files are named with the VSAM component name followed by “.VSM”. The Tachyon Operating System will be unable to process a VSAM file if its associated workstation files are renamed. You can move a VSAM file from one directory (or even machine) to another as long as you move all of the associated workstation files.

VSAM records are stored in Control Intervals. VSAM Control Intervals created by the Tachyon Operating System are compatible with those created by OS/390. VSAM Control Intervals are grouped into Control Areas. OS/390 Control Area sizes are based on the underlying disk geometry. Because this does not apply to VSAM files created by the Tachyon Operating System, the Control Areas sizes are not related to the sizes chosen by OS/390.

While the data component records of VSAM files are completely compatible between the Tachyon Operating System and OS/390, the index component records are not. The index record format used by OS/390 compresses the key information. Key compression and decompression would impact performance of the Tachyon Operating System, so an uncompressed format was designed. This means that programs that process VSAM index records and Control Intervals directly will not operate when run using the Tachyon Operating System.

The Tachyon Operating System does not allow a data or index component to be allocated or opened separately. Only a cluster may be allocated or opened.

UNIX Files

UNIX files are simply workstation files in the directory specified as the UNIX System Services root directory or a subdirectory of the root directory. The root directory is specified via the ROOT PATH parameter of the BPXPRMxx.ini configuration file. UNIX files are accessed via the UNIX Systems Services callable services such as BPX1OPN (open), BPX1RED (read) and BPX1WRT (write).

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Last modified on January 2, 2006