Tape and diskette files can be created as source files. When device files are used as source files, the record length must include the sequence number and date fields.
Any maximum record length restrictions must consider these additional 12 characters. For example, the maximum record length for a tape record is 32 766. If data is to be processed as source input, the actual tape data record has a maximum length of 32 754 (which is 32 766 minus 12).
If you open source device files for input, the system adds the sequence number and date fields, but there are zeros in the date fields.
If you open a device file for output and the file is defined as a source file, the system deletes the sequence number and date before writing the data to the device.