Magnetic tape interface

Offset	Bytes in Length	Field Name	Description
12(0C)	4	DCBBLKCT	Number of blocks in the file on the current volume to the current position.
16(10)	1	DCBTRTCH	Tape recording technique for 7-track tape.
			Code
		0010 0011	E Even parity.
		0011 1011	T BCD/EBCDIC conversion.
		0001 0011	C Data conversion.
		0010 1011	ET Even parity and conversion. Tape recording technique for a magnetic tape subsystem with Improved Data Recording Capability. Use TRTCH to override the system default value.
		0000 1000	COMP Record data in compacted format.
		0000 0100	NOCOMP Record data in standard format.
17(11)	1	DCBDEVT	Device type.
		1000 ....	Class of device. This code means magnetic tape.
		.... xxxx	Type of magnetic tape.
18(12)	1	DCBDEN	Tape density—3400 series magnetic tape units.
			Code
		0100 0011	1 556 BPI (7-track) N/A (9-track) N/A (18-track)
		1000 0011	2 800 BPI (7-track) 800 (9-track) N/A (18-track)
		1100 0011	3 N/A BPI (7-track) 1600 (9-track) N/A (18-track)
		1101 0011	4 N/A BPI (7-track) 6250 (9-track) N/A (18-track)