Using Magnetic Tape

Format-F, format-V, format-D, and format-U records are acceptable for magnetic tape. Format-V records are not acceptable on 7-track tape if the data conversion feature is not available. ASCII records are not acceptable on 7-track tape.

When you create a tape data set with variable-length record format-V or format-D, the control program pads any data block shorter than 18 bytes. For format-V records, it pads to the right with binary zeros so that the data block length equals 18 bytes. For format-D (ASCII) records, the padding consists of ASCII circumflex characters, which are equivalent to X'5E's.

Note that there is no minimum requirement for block size. However, in nonreturn-to-zero-inverted mode, if a data check occurs on a magnetic tape device, any record shorter than 12 bytes in a read operation will be treated as a noise record and lost. No check for noise will be made unless a data check occurs.

Table 1 shows how the tape density (DEN) specifies the recording density in bits per inch per track.

Table 1. Tape density (DEN) values
DEN	7-Track Tape	9-Track Tape
1	556 (NRZI)	N/A
2	800 (NRZI)	800 (NRZI)¹
3	N/A	1600 (PE)²
4	N/A	6250 (GCR)³
Note: NRZI is for nonreturn-to-zero-inverted mode. PE is for phase encoded mode. GCR is for group coded recording mode.

When DEN is not specified, the highest density capable by the unit will be used. The DEN parameter has no effect on an 18-track or 36-track tape cartridge.

The track recording technique (TRTCH) for 7-track tape can be specified as follows.

Value	Meaning
C	Data conversion is to be used. Data conversion makes it possible to write 8 binary bits of data on 7 tracks. Otherwise, only 6 bits of an 8-bit byte are recorded. The length field of format-V records contains binary data and is not recorded correctly without data conversion.
E	Even parity is to be used. If E is omitted, odd parity is assumed.
T	BCDIC to EBCDIC conversion is required.

The track recording technique (TRTCH) for magnetic tape drives with Improved Data Recording Capability can be specified as:

Value	Meaning
COMP	Data is written in compacted format.
NOCOMP	Data is written in standard format.

The system programmer sets the 3480 default for COMP or NOCOMP in the DEVSUPxx member of SYS1.PARMLIB.