XMIT

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XMIT (modified from TRANSMIT, English for transmit) is a command for the command line interpreter TSO / E for IBM mainframes , as well as the name for a proprietary file format created with it . It is used to exchange files or data (usually complete datasets ), as well as messages from mainframes to each other or from mainframes and other systems. The file extension is .XMIT or, depending on the system, also XMI, XMT, XM or XMITFILE. XMIT was introduced with the mainframe operating system MVS SP / 1 around 1980.

XMIT is still used, for example via JES2 / JES3 under z / OS . For historical purposes it is also often used when using the Hercules emulator under MVS. Almost all files in the magnetic tape archive on CBTTAPE.ORG are in this format (also compressed as a ZIP file ).

Third-party programs exist to allow viewing or extracting files under Windows, Linux, MacOS or other mainframe operating systems. The translation between EBCDIC and ASCII (if necessary and desired) takes place automatically. Used libraries and ISPF statistics are retained.

Contents of the container

As standard, complete PDS or PDS / E files ( Partitioned Data Sets ) are used, which can contain mixed content such as text files (often source code ), binary files (.BIN), object code (.PGM) or other XMIT files. Messages (.MSGS) can also or exclusively be added.

It is also possible to incorporate only sequential data (.DATA).

Since there are usually no file extensions on other systems when extracting, the type of file, the file format and the encoding (ASCII / EBCDIC) is sometimes unclear. Documentation files usually provide information about this. Commercial file viewers can use the headers, e.g. For example, recognize multi-nested or multi-compressed files and extract files from other file formats, such as AWS tape files.

The individual files are organized as partitions, so-called members . The syntax for creating an XMIT file is: 

XMIT node.user DA(file.name) OUTDATASET(out.xmi)

Options

In addition to the selection of the user (addresseelist) and the datasets, there are a few options that can be selected. Password assignment, encryption, log recording, confirmation of receipt and the like are possible.

transmission

The transmission must be binary . The file length (LRECL) of the target file is normally 80, which corresponds to the punch card standard. The data record format (RECFM) is usually FB (fixed blocked) and the data set organization value (DSORG) is PS (physical sequential).

XMIT can also be used in place of the TRANSMIT command. The counter command for receiving is RECEIVE. Example: 

RECEIVE INDATASET(x.xmi)

Alternatives

Alternative programs for data exchange are IND $ FILE (usually contained in Tn3270 programs) or the later DFDSS (Data facility data set services), both also from IBM. Furthermore, depending on the operating system, protocols and standards such as FTP , Kermit , ISPF C / S or INWMUTIL can be used.

As an alternative to uploading under emulators, the Hercules tool DASDLOAD can also be used, which creates DASD tape files from XMIT files. In addition, XMIT files can be read in using a virtual punch card reader.

Other programs

There are other programs based on XMIT, such as XMITIP, which enables an exchange via e-mail.

Since the source code of IBM software from third parties and private individuals is usually not available, reverse engineering is often used.

Individual evidence

  1. ↑ TRANSMIT MESSAGES (IBM manual)
  2. ↑ File extensions supported by unXmit (Sourceforge.net)
  3. ↑ Newsgroups derkeiler
  4. ↑ TRANSMIT under z / OS (IBM manuals)
  5. ↑ XMIT viewer and manager for Windows, Linux, MacOS on CBTTAPE.ORG
  6. ↑ TRANSMIT command overview with options
  7. ↑ XMITIP
  8. ↑ IND $ FILE page from an IBM partner
  9. ↑ Reverse Engineering (IBM developerWorks)

Web links