Data control block

Offset	Bytes in Length	Field Name	Description
16(10)	1	DCBKEYLE	Key length.
17(11)	1	DCBDEVT	Device type.
20(14)	1	DCBBUFNO	Number of buffers required for this data set: 0-255.
21(15)	3	DCBBUFCA	Address of buffer pool control block.
24(18)	2	DCBBUFL	Length of buffer: 0 - 32760 bytes.
32(20)	1	DCBBFALN	Buffer alignment
			Code
		.... ..xx	Reserved bits.
		.... ..10	D Doubleword boundary.
		.... ..01	F Fullword not a doubleword boundary, coded in the DCB macro.
		.... ..11	F Fullword not a doubleword boundary, coded in the DD statement.
33(21)	3	DCBEODA	Address of a user-provided routine to handle end-of-data conditions.
36(24)	1	DCBRECFM	Record format.
			Code
		10.. ....	F Fixed length records.
		01.. ....	V Variable length records.
		11.. ....	U Undefined length records.
		..1. ....	T Track overflow.
		...1 ....	B Blocked records. Cannot occur with undefined (U).
		.... 1...	S Standard records. No truncated blocks or unfilled tracks are embedded in the data set.
		.... .10.	A ISO/ANSI control character.
		.... .01.	M Machine control character.
		.... .00.	No control character.
		.... ...1	Key length (KEYLEN) was specified in the DCB macro; this bit is inspected by the open routine to prevent overriding a specification of KEYLEN=0 by a nonzero specification in the JFCB or data set label.
37(25)	3	DCBEXLSA	Exit list. Address of a user-provided list.
42(2A)	2	DCBMACRF	Macro reference after OPEN: Contents and meaning are the same as those of the DCBMACR field before OPEN.
50(32)	2	DCBMACR	Macro reference before OPEN: specifies the major macros and various options associated with them. Used by the open routine to determine access method. Used by the access method executors with other parameters to determine which load modules are required.
			Code
50(32)		Byte 1	BISAM
		00.0 0...	Always zero for BISAM.
		..1. ....	R READ
		.... .1..	S Dynamic buffering.
		.... ..1.	C CHECK
		.... ...x	Reserved bit.
51(33)		Byte 2	BISAM
		00.0 0000	Always zero for BISAM.
		..1. ....	W WRITE
50(32)		Byte 1	QISAM
		0.0. .0..	Always zero for BISAM.
		.1.. ....	G GET
		...1 ....	M Move mode of GET.
		.... 1...	L Locate mode for GET.
		.... ..xx	Reserved bit.
51(33)		Byte 2	QISAM
		1... ....	S SETL
		.1.. ....	P PUT or PUTX
		..0. ....	Always zero for QISAM.
		...1 ....	M Move mode of PUT.
		.... 1...	L Locate mode for PUT.
		.... .1..	U Update in place (PUTX).
		.... ..1.	K SETL by key.
		.... ...1	I SETL by ID.
52(34)	1	DCBOPTCD	Option codes:
			Code
		1... ....	W Write-validity check.
		.1.. ....	U Full-track index write.
		..1. ....	M Master indexes.
		...1 ....	I Independent overflow area.
		.... 1...	Y Cylinder overflow area.
		.... ..1.	L Delete option.
		.... ...1	R Reorganization criteria.
		.... .x..	Reserved bit.
53(35)	1	DCBMAC	Extension of the DCBMACRF field for ISAM.
			Code
		xxxx ...x	Reserved bits.
		.... 1...	U Update for read.
		.... .1..	U Update type of write.
		.... ..1.	A Add type of write.
54(36)	1	DCBNTM	Number of tracks that determines the development of a master index. Maximum permissible value: 99.
55(37)	1	DCBCYLOF	The number of tracks to be reserved on each prime data cylinder for records that overflow from other tracks on that cylinder. To determine how to calculate the maximum number, see the section on allocating space for an indexed sequential data set in z/OS DFSMS Using Data Sets.
56(38)	4	DCBSYNAD	Address of user's synchronous error routine to be entered when uncorrectable errors are detected in processing data records.
60(3C)	2	DCBRKP	Relative position of the first byte of the key in each logical record. Maximum permissible value: logical record length minus key length.
62(3E)	2	DCBBLKSI	Block size.
64(40)	4	DCBMSWA	Address of the storage work area reserved for use by the control program when new records are being added to an existing data set. The DCBMSWA field contains significant information only when the data set is opened for BISAM.
68(44)	2	DCBSMSI	Number of bytes in area reserved to hold the highest level index. The DCBSMSI field contains significant information only when the data set is opened for BISAM.
70(46)	2	DCBSMSW	Number of bytes in work area used by control program when new records are being added to the data set. The DCBSMSW field contains significant information only when the data set is opened for BISAM.
72(48)	1	DCBNCP	Number of copies of the READ-WRITE (type K) channel programs that are to be established for this data control block (99 maximum).
73(49)	3	DCBMSHIA	Address of the storage area holding the highest level index.
80(50)	1	DCBEXCD1	First byte in which exceptional conditions detected in processing data records are reported to the user.
		1... ....	Lower key limit not found.
		.1.. ....	Invalid device address for lower limit (QISAM only). Record length check (BISAM only).
		..1. ....	Space not found.
		...1 ....	Invalid request.
		.... 1...	Uncorrectable input error.
		.... .1..	Uncorrectable output error (BISAM only). Block could not be reached (BISAM only).
		.... ..1.	Block could not be reached (input) (QISAM only). Overflow record (BISAM only).
		.... ...1	Block could not be reached (update) (QISAM only). Duplicate record (BISAM only).
81(51)	1	DCBEXCD2	Second byte in which exceptional conditions detected in processing data records are reported to the user (QISAM only).
		1... ....	Sequence check.
		.1.. ....	Duplicate record.
		..1. ....	DCB closed when error was detected.
		...1 ....	Overflow record.
		.... 1...	PUT: length field of record larger than length indicated in DCBLRECL.
		.... .xxx	Reserved bits.
82(52)	2	DCBLRECL	Logical record length for fixed-length record formats. Variable-length record formats: maximum logical record length or an actual logical record length changed dynamically by the user when creating the data set.
150(96)	2	DCBNCRHI	Number of storage locations needed to hold the highest level index.
197(C5)	1	DCBOVDEV	Device type for independent overflow.