IOB

Common Name:

Input/Output Block

Macro Name:

IEZIOB

DSECT Name:

IOB (DSECT card precedes prefix); label, IOBSTDRD should be used in the USING statement for the standard section.

Eye-Catcher ID:

None

Subpool and Key:

Any subpool, user key

Size:

Variable

Created by:

Access method OPEN executor or by application program

Pointed to by:

DCBIOBAD field of the DCB data area
DCBIOBA field of the DCB data area
IOBNIOBA field of the IOB data area
RQEIOB field of the IOB data area (depending on access method used)
QPLIOB field of the QPL data area
TCBIOBRC field of the TCB data area (for first quiesced TCB)

Serialization:

The user is responsible for serialization. The LOCAL lock is held during I/O interrupt processing. The way IOBs are chained and serialized depends on the access method used.

Function:

The IOB is the communications medium between a routine that requests an I/O operation and the I/O supervisor's needs to execute the I/O operation.

Note: This section includes fields that are added to the IOB by various access methods. The general use fields that are intended as programming interfaces are described in z/OS DFSMSdfp Advanced Services.

Offset	Type/Value	Len	Name (Dim)	Description
PREFIX SECTIONS OF THE IOB
–16 (–10)	DBL WORD	8	IOBPREFX(0)
QSAM, BSAM, BPAM PREFIX CHAINED SCHEDULING 16 BYTES
–16 (–10)	DBL WORD	8	IOBQSAMC (0)
–16 (–10)	DBL WORD	8	IOBBSAMC (0)
–16 (–10)	DBL WORD	8	IOBBPAMC (0)
–16 (–10)	BITSTRING	1	IOBCFLG1	– I/O INDICATORS
	1. . . . . . .		IOBV6CHN	"X'80'"– I/O CHAINED BIT SET BY IGG019V6
	.1. . . . . .		IOBRSV02	"X'40',,CX'X'"RESERVED
	. .1. . . . .		IOBRSV03	"X'20',,CX'X'"RESERVED
	. . .1 . . . .		IOBRSV04	"X'10',,CX'X'"RESERVED
	. . . . 1. . .		IOBPTST	"X'08'"– NOTE OR POINT OPERATION IS IN PROCESS.
	. . . . .1. .		IOBABAPP	"X'04'"– ERROR HAS BEEN PROCESSED ONCE BY ABNORMAL–END APPENDAGE ROUTINE.
	. . . . . .1.		IOBRSTCH	"X'02'"– RESTART CHANNEL
	. . . . . . .1		IOBPCI	"X'01'"– SET WHEN A PROGRAM– CONTROLLED INTERRUPTION (PCI) OCCURS
–15 (–F)	BITSTRING	1	IOBRSV05	– RESERVED
–14 (–E)	CHARACTER	1	IOBCINOP	– OFFSET OF THE LAST I/O COMMAND FOR INPUT OPERATION (NOP CCW) FROM THE ORIGIN OF THE ICB
–13 (–D)	CHARACTER	1	IOBCONOP	– OFFSET OF THE LAST I/O COMMAND FOR AN OUTPUT OPERATION (NOP CCW) FROM THE ORIGIN OF THE ICB
–12 (–C)	SIGNED	4	IOBCECB	– EVENT CONTROL BLOCK USED BY BSAM OR QSAM. SHOWS THE STATUS OF THE I/O OPERATION.
–8 (–8)	ADDRESS	4	IOBCICB	– ADDRESS OF THE FIRST INTERRUPT CONTROL BLOCK (ICB) ON THE ICB QUEUE
–4 (–4)	ADDRESS	4	IOBCNOPA	– ADDRESS OF THE NOP COMMAND AT THE END OF THE QUEUE
QSAM, BSAM, BPAM PREFIX NORMAL SCHEDULING 8 BYTES
–8 (–8)	DBL WORD	8	IOBQSAMN (0)
–8 (–8)	DBL WORD	8	IOBBSAMN (0)
–8 (–8)	DBL WORD	8	IOBBPAMN (0)
–8 (–8)	ADDRESS	4	IOBNIOBA (0)	– ADDRESS OF THE NEXT IOB ASSOCIATED WITH ONE PARTICULAR DCB. THE IOB'S ARE CHAINED IN SEQUENTIAL ORDER.
–8 (–8)	BITSTRING	1	IOBNFLG1	– FLAG BYTE
	1. . . . . . .		IOBPRTOV	"X'80'"– PRTOV HAS OCCURRED (PRINTER DEVICES) (MDC331).
	1. . . . . . .		IOBSEGMT	"X'80'"– SEGMENTING OF A SPANNED RECORD IS IN PROCESS (QSAM LOCATE MODE, LOGICAL RECORD INTERFACE, UPDATE PROCESSING) (DIRECT ACCESS) (OS/VS2) (MDC332).
	.1. . . . . .		IOBWRITE	"X'40'"– A WRITE OPERATION IS IN PROCESS.
	. .1. . . . .		IOBREAD	"X'20'"– A READ OPERATION IS IN PROCESS.
	. . .1 . . . .		IOBUPDAT	"X'10'"– UPDATE FLAG. SET ON TOGETHER WITH BIT 1 OF THIS BYTE TO SHOW THAT THE BLOCK IS TO BE UPDATED. CAN ONLY OCCUR IF THE OPEN PARAMETER IS UPDAT.
	. . . . 1. . .		IOBBKSPC	"X'08'"– IOB BEING USED FOR BACKSPACE, CONTROL, OR NOTE/POINT OPERATION
	. . . . .1. .		IOBSPAN	"X'04'"– THE RECORD CURRENTLY BEING PROCESSED HAS MORE THAN ONE SEGMENT (QSAM LOCATE MODE, LOGICAL RECORD INTERFACE, UPDATE PROCESSING OF SPANNED RECORDS).
	. . . . . .1.		IOBUPERR	"X'02'"– UPDATE CHANNEL PROGRAM HAS BEEN SPLIT INTO TWO PARTS (MDC036).
	. . . . . . .1		IOBFIRST	"X'01'"– THIS IS THE FIRST IOB ON CHAIN.
–7 (–7)	ADDRESS	3	IOBNIOBB	– ADDRESS OF THE NEXT IOB ASSOCIATED WITH ONE PARTICULAR DCB. THE IOBS ARE CHAINED IN SEQUENTIAL ORDER.
–4 (–4)	SIGNED	4	IOBNECB	– EVENT CONTROL BLOCK USED BY QSAM TO INDICATE THE STATUS OF THE I/O EVENT
BDAM PREFIX 8 BYTES
–8 (–8)	DBL WORD	8	IOBBDAM (0)
–8 (–8)	ADDRESS	4	IOBDQADA (0)	– ADDRESS OF THE OTHER IOB REFERRED TO IN DESCRIPTION OF IOBDEQ BELOW
–8 (–8)	BITSTRING	1	IOBDEQIN	– DEQUEUE LOOP INDICATOR
	1. . . . . . .		IOBDEQ	"X'80'"– THIS IOB IS USING A TRACK THAT WAS DEQUEUED BY ANOTHER IOB, WHICH IS NOW WAITING TO DEQUEUE ANOTHER TRACK. THE OTHER IOB ENQUEUED ON TWO OR MORE TRACKS TO FIND SPACE IN WHICH TO WRITE/ADD A SPANNED RECORD. THE OTHER IOB REMAINED ENQUEUED UNTIL IT EITHER WROTE THE RECORD OR DETERMINED THAT THERE WAS ENOUGH CONTIGUOUS FREE SPACE ON THE TRACKS TO CONTAIN THE RECORD. AFTER THE OTHER IOB DEQUEUED THE CURRENT TRACK, THE DEQUEUING WAS INTERRUPTED BY THE NEED OF THIS IOB FOR THE CURRENT TRACK.
	.1. . . . . .		IOBRSV07	"X'40',,C'X'"RESERVED
	. .1. . . . .		IOBRSV08	"X'20',,C'X'"RESERVED
	. . .1 . . . .		IOBRSV09	"X'10',,C'X'"RESERVED
	. . . . 1. . .		IOBRSV10	"X'08',,C'X'"RESERVED
	. . . . .1. .		IOBRSV11	"X'04',,C'X'"RESERVED
	. . . . . .1.		IOBRSV12	"X'02',,C'X'"RESERVED
	. . . . . . .1		IOBRSV13	"X'01',,C'X'"RESERVED
–7 (–7)	ADDRESS	3	IOBDQADB	– ADDRESS OF THE OTHER IOB REFERRED TO IN DESCRIPTION OF IOBDEQ ABOVE
–4 (–4)	ADDRESS	4	IOBSWAP	– ADDRESS OF THE SEGMENT WORK AREA USED BY THIS IOB TO READ OR WRITE A RECORD OF A FORMAT VS DATA SET
GAM, QISAM PREFIX 4 BYTES
–4 (–4)	SIGNED	4	IOBGQECB	– EVENT CONTROL BLOCK THAT IS WITHIN FIRST IOB ONLY (GAM) EVENT CONTROL BLOCK USED TO INDICATE STATUS OF AN I/O EVENT (QISAM)
STANDARD SECTION OF THE IOB
0 (0)	DBL WORD	8	IOBSTDRD (0)
0 (0)	BITSTRING	1	IOBFLAG1	– FLAG BYTE 1
	1. . . . . . .		IOBDATCH	"X'80'"– DATA CHAINING USED IN CHANNEL PROGRAM
	.1. . . . . .		IOBCMDCH	"X'40'"– COMMAND CHAINING USED IN CHANNEL PROGRAM
	. .1. . . . .		IOBERRTN	"X'20'"– ERROR ROUTINE IS IN CONTROL.
	. . .1 . . . .		IOBRPSTN	"X'10'"– DEVICE IS TO BE REPOSITIONED.
	. . . . 1. . .		IOBCYCCK	"X'08'"— CYCLIC REDUNDANCY CHECK (CRC) NEEDED (TAPE)
	. . . . 1. . .		IOBFCREX	"X'08'"– FETCH COMMAND RETRY EXIT (DIRECT ACCESS)
	. . . . .1. .		IOBIOERR	"X'04'"– EXCEPTIONAL CONDITION. AFTER THE ERROR ROUTINE RETURNS AND THIS BIT IS ON, THE ERROR IS CONSIDERED PERMANENT.
	. . . . . .1.		IOBUNREL	"X'02'"– IOB UNRELATED FLAG (THAT IS, NONSEQUENTIAL)
	. . . . . . .1		IOBRSTRT	"X'01'"– IF 1, RESTART ADDRESS IN IOB TO BE USED. IF 0, START. (OS/VS1) MDC034
	. . . . . . .1		IOBSPSVC	"X'01'"– FOR SAM/PAM, SET BY SVC IF I/O APPENDAGE SHOULD NOT PROCESS INTERRUPT (OS/VS2) MDC035
1 (1)	BITSTRING	1	IOBFLAG2	– FLAG BYTE 2
	1. . . . . . .		IOBHALT	"X'80'"– HALT I/O HAS BEEN ISSUED BY SVC PURGE ROUTINE
	.1. . . . . .		IOBSENSE	"X'40'"– SENSE WILL NOT BE PERFORMED UNTIL THE DEVICE IS FREE
	. .1. . . . .		IOBPURGE	"X'20'"–IOB HAS BEEN PURGED TO ALLOW I/O ACTIVITY TO QUIESCE. (OS/VS1) MDC046
	. .1. . . . .		IOBRRT3	"X'20'"– TYPE 3 RELATED REQUEST (OS/VS2) MDC048
	. . .1 . . . .		IOBRDHA0	"X'10'"– HOME ADDRESS (R0) RECORD IS TO BE READ. SEEK COMMAND NOT NEEDED. (OS/VS1) MDC047
	. . .1 . . . .		IOBRRT2	"X'10'"– TYPE 2 RELATED REQUEST (OS/VS2) MDC049
	. . . . 1. . .		IOBALTTR	"X'08'"– NO TEST FOR OUT–OF–EXTENT. AN ALTERNATE TRACK IS IN USE.
	. . . . .1. .		IOBSKUPD	"X'04'"– SEEK ADDRESS IS BEING UPDATED. CYLINDER END OR FILE MASK VIOLATION HAS OCCURRED.
	. . . . . .1.		IOBSTATO	"X'02'"– DEVICE END STATUS HAS BEEN OR'ED WITH CHANNEL END STATUS (GRAPHICS DEVICE)
	. . . . . . .1		IOBPNCH	"X'01'"– ERROR RECOVERY IN CONTROL FOR A 2540 CARD PUNCH WITH THREE BUFFERS (QSAM) RESETPL MACRO INSTRUCTION WAS USED (BTAM)
2 (2)	BITSTRING	1	IOBSENS0	– FIRST SENSE BYTE
	1. . . . . . .		IOBS0B0	"X'80'"– BIT 0 (DEVICE DEPENDENT)
	.1. . . . . .		IOBS0B1	"X'40'"– BIT 1 (DEVICE DEPENDENT)
	. .1. . . . .		IOBS0B2	"X'20'"– BIT 2 (DEVICE DEPENDENT)
	. . .1 . . . .		IOBS0B3	"X'10'"– BIT 3 (DEVICE DEPENDENT)
	. . . . 1. . .		IOBS0B4	"X'08'"– BIT 4 (DEVICE DEPENDENT)
	. . . . .1. .		IOBS0B5	"X'04'"– BIT 5 (DEVICE DEPENDENT)
	. . . . . .1.		IOBS0B6	"X'02'"– BIT 6 (DEVICE DEPENDENT)
	. . . . . . .1		IOBS0B7	"X'01'"– BIT 7 (DEVICE DEPENDENT)
	. . . . . . .1		IOBSNSC9	"X'01'"– CHANNEL 9 SENSED IN CARRIAGE TAPE
3 (3)	BITSTRING	1	IOBSENS1	– SECOND SENSE BYTE
	1. . . . . . .		IOBS1B0	"X'80'"– BIT 0 (DEVICE DEPENDENT)
	1. . . . . . .		IOBS1B1	"X'40'"– BIT 1 (DEVICE DEPENDENT)
	. .1. . . . .		IOBS1B2	"X'20'"– BIT 2 (DEVICE DEPENDENT)
	. . .1 . . . .		IOBS1B3	"X'10'"– BIT 3 (DEVICE DEPENDENT)
1	. . . . 1. . .		IOBS1B4	"X'08'"– BIT 4 (DEVICE DEPENDENT)
	. . . . .1. .		IOBS1B5	"X'04'"– BIT 5 (DEVICE DEPENDENT)
	. . . . . .1.		IOBS1B6	"X'02'"– BIT 6 (DEVICE DEPENDENT)
	. . . . . . .1		IOBS1B7	"X'01'"– BIT 7 (DEVICE DEPENDENT)
4 (4)	ADDRESS	4	IOBECBPT (0)	– ADDRESS OF ECB TO BE POSTED ON I/O COMPLETION
4 (4)	CHARACTER	1	IOBECBCC	– COMPLETION CODE FOR AN I/O REQUEST. THIS CODE WILL APPEAR IN THE FIRST BYTE OF AN ECB.
5 (5)	ADDRESS	3	IOBECBPB	–ADDRESS OF THE ECB TO BE POSTED UPON THE COMPLETION OF AN I/O EVENT. FOR BSAM/BPAM, ECB IS IN THE DECB. FOR QSAM, ECB IS IN THE QSAM PREFIX OF THE IOB.
8 (8)	BITSTRING	1	IOBFLAG3 (0)	– I/O SUPERVISOR ERROR ROUTINE FLAG BYTE (DEVICE DEPENDENT)
8 (8)	BITSTRING	1	IOBFL3	– FLAG 3 – STATUS ERROR COUNTS FOR MAGNETIC DOCUMENT READER (3890) OR FLAGS FOR 3800 (OS/VS1) (MDC307)
	1. . . . . . .		IOBCCC	"X'80'"– CHANNEL CONTROL CHECK ERROR COUNT (3890) MDC038
	.1. . . . . .		IOBICC	"X'40'"– INTERFACE CONTROL CHECK ERROR COUNT (3890) MDC039
	. .1. . . . .		IOBCDC	"X'20'"– CHANNEL DATA CHECK ERROR (3890) MDC040
	. . .1 . . . .		IOBACU	"X'10'"– ATTENTION/CONTROL UNIT ERROR (3890) MDC041
	. . . . 1. . .		IOBCNC	"X'08'"– CHAIN CHECK ERROR (3890) MDC042
	. . . . 1. . .		IOBSDR	"X'08'"– STATISTICS ONLY FLAG (3800) (MDC306)
	. . . . .1. .		IOBMSG	"X'04'"– MESSAGE FLAG (3890 OR 3800) (MDC308)
	. . . . . .1.		IOBICL	"X'02'"– INCORRECT LENGTH ERROR (3890) MDC020
	. . . . . .1.		IOBJAM	"X'02'"– SET ON WHEN JES SUBSYSTEM HAS DETECTED A PAPER JAM SO 3800 ERP WILL SUPPRESS ITS INTERVENTION REQUIRED MESSAGE (3800) (MDC330)
	. . . . . . .1		IOBLOG	"X'01'"– LOG OUT FLAG (3890 OR 3800) (MDC309)
9 (9)	CHARACTER	7	IOBCSW (0)	– LOW–ORDER SEVEN BYTES OF THE LAST CSW THAT REFLECTS THE STATUS FOR THIS REQUEST
9 (9)	CHARACTER	5	IOBIOCSW (0)	– LOW–ORDER BYTES OF CSW FOR MAGNETIC DOCUMENT READER (3890) (OS/VS1) MDC022
9 (9)	ADDRESS	3	IOBCMDA	– COMMAND ADDRESS (3890) MDC023
12 (C)	BITSTRING	2	IOBSTBYT (0)	– STATUS BITS 32–47 (3890) MDC024
12 (C)	BITSTRING	1	IOBUSTAT	– CSW UNIT STATUS FLAGS (3800) (MDC311)
	1. . . . . . .		IOBUSB0	"X'80'"– ATTENTION (MDC312)
	.1. . . . . .		IOBUSB1	"X'40'"– STATUS MODIFIER (MDC313)
	. .1. . . . .		IOBUSB2	"X'20'"– CONTROL UNIT END (MDC314)
	. . .1 . . . .		IOBUSB3	"X'10'"– BUSY (MDC315)
	. . . . 1. . .		IOBUSB4	"X'08'"– CHANNEL END (MDC316)
	. . . . .1. .		IOBUSB5	"X'04'"– DEVICE END (MDC317)
	. . . . . .1.		IOBUSB6	"X'02'"– UNIT CHECK (MDC318)
	. . . . . . .1		IOBUSB7	"X'01'"– UNIT EXCEPTION (MDC319)
13 (D)	BITSTRING	1	IOBCSTAT	– CSW CHANNEL STATUS FLAGS (3800) (MDC320)
	1. . . . . . .		IOBCSB0	"X'80'"– PROGRAM CONTROL INTERRUPT (MDC321)
	.1. . . . . .		IOBCSB1	"X'40'"– INCORRECT LENGTH (MDC322)
	. .1. . . . .		IOBCSB2	"X'20'"– PROGRAM CHECK (MDC323)
	. . .1 . . . .		IOBCSB3	"X'10'"– PROTECTION CHECK (MDC324)
	. . . . 1. . .		IOBCSB4	"X'08'"– CHANNEL DATA CHECK (MDC325)
	. . . . .1. .		IOBCSB5	"X'04'"– CHANNEL CONTROL CHECK (MDC326)
	. . . . . .1.		IOBCSB6	"X'02'"– INTERFACE CONTROL CHECK (MDC327)
	. . . . . . .1		IOBCSB7	"X'01'"– CHAINING CHECK (MDC328)
14 (E)	BITSTRING	2		– LAST TWO BYTES OF IOBCSW
16 (10)	ADDRESS	4	IOBSTART (0)	– ADDRESS OF CHANNEL PROGRAM TO BE EXECUTED
16 (10)	BITSTRING	1	IOBSIOCC	– SIO CODE. BITS 2 AND 3 CONTAIN CONDITION CODE RETURNED AFTER EXECUTION OF SIO INSTRUCTION FOR THIS I/O EVENT.
17 (11)	ADDRESS	3	IOBSTRTB	– ADDRESS OF CHANNEL PROGRAM TO BE EXECUTED
20 (14)	ADDRESS	4	IOBDCBPT (0)	– ADDRESS OF DCB ASSOCIATED WITH THIS IOB
20 (14)	BITSTRING	1	IOBFLAG4	– FLAG BYTE MDC011
	1. . . . . . .		IOBGDPOL	"X'80'"– RE–ENTER SIO APPENDAGE FOR OLTEP GUARANTEED DEVICE PATH MDC012
	.1. . . . . .		IOBCC3WE	"X'40'"– USER REQUESTS THAT IOS POST A X'6D' FOR A CONDITION CODE 3 ON ATTEMPTED I/O OPERATIONS (OS/VS2) (MDC310)
	. .1. . . . .		IOBPMERR	"X'20'"– VTAM® SETS THIS BIT ON TO INDICATE TO IOS THAT VTAM SHOULD BE POSTED WITH A PERMANENT I/O ERROR BECAUSE ALL ALTERNATE PATHS TO THE 3705 HAVE BEEN TRIED (OS/VS1) (MDC329)
	. . .1 . . . .		IOBCEF	"X'10'"– IOB COMMON EXTENSION IS AVAILABLE
	. . . . 1. . .		IOBRSV41	"X'08',,C'X'"– RESERVED
	. . . . .1. .		IOBRSV42	"X'04',,C'X'"– RESERVED
	. . . . . .1.		IOBJES3I	"X'02'"– JES3 INTERVENTION REQUIRED NOTIFICATION. SETTING THIS BIT WILL RESULT IN TURNING ON BIT IOSPGDPX IN THE IOSB. (OS/VS2)(MDC305)
	. . . . . . .1		IOBRSV44	"X'01',,C'X'"– RESERVED
21 (15)	ADDRESS	3	IOBDCBPB	– ADDRESS OF DCB ASSOCIATED WITH THIS IOB
24 (18)	ADDRESS	4	IOBRESTR (0)	– AFTER SVC 16 (PURGE) – QUIESCE – ADDRESS OF THE NEXT IOB IN THE PURGE CHAIN. (LAST IOB IN THE CHAIN, BYTE 4 IS FF.) DURING I/O SUPERVISOR WRITE-TO-OPERATOR ROUTINE CONTROL - CCHH PART OF THE ADDRESS OF A DEFECTIVE TRACK. DURING I/O ERROR CORRECTION (MEANINGFUL ONLY IF BIT 3 IN THE IOBFLAG1 FIELD IS ON) – ADDRESS OF THE CHANNEL PROGRAM USED TO CORRECT AN ERROR CONDITION. AFTER I/O ERROR CORRECTION – IF A CHANNEL PROGRAM IS RESTARTED THROUGH A CCW OTHER THAN THE ONE POINTED TO BY THE IOBSTART FIELD, ITS ADDRESS IS HERE.
24 (18)	CHARACTER	1	IOBREPOS	– DURING I/O ERROR CORRECTION (MEANINGFUL ONLY IF BIT 3 IN THE IOBFLAG1 FIELD IS ON) FOR MAGNETIC TAPE ONLY – THE CONTROL COMMAND (BSR, FSR, ERG) REQUIRED TO REPOSITION OVER A BLOCK.
25 (19)	ADDRESS	3	IOBRSTRB	– SAME AS IOBRESTR ABOVE
28 (1C)	SIGNED	2	IOBINCAM (0)	– QSAM, BSAM, EXCP ACCESS METHOD – NORMAL SCHEDULING – VALUE USED TO INCREMENT BLOCK COUNT FIELD IN DCB FOR MAGNETIC TAPE. CHAINED SCHEDULING – ZEROS. QSAM, BSAM – OPERATION CODE OF WRITE CCW WHEN A USASI CONTROL CHARACTER AND NO DATA IS TO BE WRITTEN (PRINTER AND CARD PUNCH ONLY)
28 (1C)	BITSTRING	1	IOBBTAMF	– FLAG BYTE FOR BTAM
	1. . . . . . .		IOBPRMER	"X'80'"– SAD OR ENABLE ISSUED BY OPEN RESULTED IN A PERMANENT I/O ERROR
	.1. . . . . .		IOBINUSE	"X'40'"– THIS IOB IS CURRENTLY IN USE BY AN I/O OPERATION
	. .1. . . . .		IOBRSV14	"X'20',,C'X'"RESERVED
	. . .1 . . . .		IOBRSV15	"X'10',,C'X'"RESERVED
	. . . . 1. . .		IOBRSV16	"X'08',,C'X'"RESERVED
	. . . . .1. .		IOBRSV17	"X'04',,C'X'"RESERVED
	. . . . . .1.		IOBRFTMG	"X'02''"– A REQUEST–FOR–TEST MESSAGE RECEIVED FROM A REMOTE 3270 DISPLAY STATION ICB478
	. . . . . . .1		IOBOLTST	"X'01'"– LINE IS UNDER ON– LINE TEST OPERATION
29 (1D)	BITSTRING	1	IOBRSV19	–RESERVED
28 (1C)	BITSTRING	1	IOBFL4	– FLAG 4 – SENSE ERROR COUNTS FOR MAGNETIC DOCUMENT READER (3890) (OS/VS1) OR ERROR CODE PASSBACK BYTE FOR 3895 (FOR ERROR CODE VALUES, SEE IBM® 3895 DOCUMENT READER/INSCRIBER MACHINE AND PROGRAMMING DESCRIPTION, GA24–3620) (MDC333)
	1. . . . . . .		IOBOVR	"X'80'"– OVERRUN ERROR (3890) (MDC026)
	.1. . . . . .		IOBREJ	"X'40'"– COMMAND REJECT ERROR (3890) (MDC027)
	. .1. . . . .		IOBDCK	"X'20'"– DATA CHECK ERROR (3890) (MDC028)
	. . .1 . . . .		IOBBUS	"X'10'"– BUS–OUT ERROR (3890) (MDC029)
	. . . . 1. . .		IOBEQP	"X'08'"– EQUIPMENT CHECK ERROR (3890) (MDC030)
	. . . . .1. .		IOBENT	"X'04'"– FIRST TIME ENTRY SWITCH (3890) (MDC045)
	. . . . . .1.		IOBRSV47	"X'02',,C'X'"– RESERVED FOR 3890 MDC044
	. . . . . . .1		IOBRSV46	"X'01',,C'X'"– RESERVED FOR 3890 MDC033
28 (1C)	CHARACTER	1	IOBCRDCC	– DATA CHECK ERROR COUNT (OPTICAL READER)
29 (1D)	CHARACTER	1	IOBCRILC	– INCORRECT LENGTH ERROR COUNT (OPTICAL READER)
28 (1C)	BITSTRING	1	IOBAMAF	PDSE DIAGNOSTICS BYTE TO DESCRIBE ERRORS DETECTED BY AMA PDSE ROUTINES
	. . . . . . .1		IOBBDFPL	"X'01'"– BAD FPL PASSED TO ASYNC COMP RTN (IGG019SY) BY JCDM
	. . . . . .1.		IOBPGMCK	"X'02'"– PROGRAM CHECK ENCOUNTERED IN IGG019SY (IGGT19SY ENTERED).
	. . . . . .11		IOBBADRC	"X'03'"– BAD RETURN CODE ENCOUNTERED FROM SMS –IOBDIAG RETURN/REASON CODES UPDATED
	. . . . .1. .		IOBBADLT	"X'04'"– INVALID LOCATOR TOKEN DETECTED BY POINT
	. . . . .1.1		IOBNCRLT	"X'05'"– RLT WAS INPUT BUT NO MEMBER WAS CONNECTED (DETECTED BY POINT)
	. . . . .11.		IOBPOUT	"X'06'"– DCB OPEN FOR OUTPUT & AN MLT FOR OTHER THAN THE CURRENT MEMBER WAS INPUT (DETECTED BY POINT)
	. . . . .111		IOBOUTIO	"X'07'"– OUTSTANDING I/O IN PROGRESS DETECTED BY POINT
	. . . . 1. . .		IOBRLTTB	"X'08'"– RLT TOO BIG (>= HWM) DETECTED BY POINT
	. . . . 1. .1		IOBFLOCK	"X'09'"– CONNECT OR RECONNECT UNABLE TO GET FILE LOCK. DETECTED BY POINT. COULD BE A USER ERROR.
	. . . . 1.1.		IOBNFILE	"X'0A'"– MLT INPUT TO POINT BUT NO SUCH FILE
30 (1E)	SIGNED	2	IOBERRCT	– USED BY I/O SUPERVISOR ERROR ROUTINES TO COUNT TEMPORARY ERRORS DURING RETRY
EXTENSION SECTIONS OF THE IOB
32 (20)	DBL WORD	8	IOBEXTEN(0)
DIRECT ACCESS EXTENSION 8 BYTES
32 (20)	CHARACTER	8	IOBSEEK (0)	– A SEEK ADDRESS (IN THE FORMAT MBBCCHHR) USED WITH A CHANNEL PROGRAM
32 (20)	CHARACTER	1	IOBM	– THE NUMBER OF THE DEB EXTENT TO BE USED FOR THIS REQUEST. THE FIRST EXTENT IS NUMBER 0.
33 (21)	CHARACTER	2	IOBBB (0)	– BIN NUMBER(DATA CELL)
33 (21)	CHARACTER	1	IOBBB1	BIN NUMBER
34 (22)	CHARACTER	1	IOBBB2	BIN NUMBER
35 (23)	CHARACTER	2	IOBCC (0)	– CYLINDER NUMBER
35 (23)	CHARACTER	1	IOBCC1	– CYLINDER NUMBER
36 (24)	CHARACTER	1	IOBCC2	– CYLINDER NUMBER
37 (25)	CHARACTER	2	IOBHH (0)	– TRACK NUMBER
37 (25)	CHARACTER	1	IOBHH1	– TRACK NUMBER
38 (26)	CHARACTER	1	IOBHH2	– TRACK NUMBER
39 (27)	CHARACTER	1	IOBR	– RECORD NUMBER
BISAM EXTENSION 16 BYTES
40 (28)	ADDRESS	4	IOBCCWAD	– FOR FIXED LENGTH RECORDS, ADDRESS OF FIRST CCW OF CHANNEL PROGRAM. FOR VARIABLE LENGTH RECORDS, ADDRESS OF BUFFER, IF DYNAMIC BUFFERING SPECIFIED, AFTER COMPLETION OF A READ FOR UPDATE (READ KU)
44 (2C)	BITSTRING	1	IOBINDCT	– INDICATORS
	1. . . . . . .		IOBDEQCP	"X'80'"– DEQUEUE CHANNEL PROGRAM FROM QUEUE
	.1. . . . . .		IOBUNSCH	"X'40'"– UNSCHEDULED QUEUE
	. .1. . . . .		IOBOVPTR	"X'20'"– IF 0, DECBAREA + 6 POINTS TO OVERFLOW RECORD DATA. IF 1, DCBMSWA POINTS TO OVERFLOW RECORD KEY FOLLOWED BY DATA.
1	. . .1 . . . .		IOBKEYAD	"X'10''"– IF 0, DECBKEY POINTS TO OVERFLOW RECORD KEY. IF 1, DCBMSWA + 8 POINTS TO OVERFLOW RECORD KEY.
	. . . . 1. . .		IOBRSV27	"X'08',,C'X'"RESERVED
	. . . . .1. .		IOBRSV28	"X'04',,C'X'"RESERVED
	. . . . . .1.		IOBRSV29	"X'02',,C'X'"RESERVED
	. . . . . . .1		IOBCHNNL	"X'01'"– IF 0, NORMAL CHANNEL END HAS OCCURRED. IF 1, ABNORMAL CHANNEL END HAS OCCURRED.
45 (2D)	BITSTRING	1	IOBUNSQR	– REASON FOR UNSCHEDULED QUEUE
	1. . . . . . .		IOBCPBSY	"X'80'"– CHANNEL PROGRAM CP1 OR CP2 BUSY
	.1. . . . . .		IOBNTAV1	"X'40'"– NO CP4, CP5 OR CP6 AVAILABLE
	. .1. . . . .		IOBNTAV2	"X'20'"– NO CP7 AVAILABLE
1	. . .1 . . . .		IOBKNWR	"X'10'"– WRITE KN IS IN EFFECT (UNSCHEDULED IOB IS FOR WRITE KN)
	. . . . 1. . .		IOBKNRWR	"X'08'"– WRITE KN IS IN EFFECT (UNSCHEDULED IOB IS FOR READ OR WRITE KN)
	. . . . .1. .		IOBRSV30	"X'04',,C'X'"RESERVED
	. . . . . .1.		IOBRSV31	"X'02',,C'X'"RESERVED
	. . . . . . .1		IOBRSV32	"X'01',,C'X'"RESERVED
46 (2E)	CHARACTER	1	IOBAPP	– APPENDAGE CODE
47 (2F)	CHARACTER	1	IOBASYN	– ASYNCHRONOUS ROUTINE CODE
48 (30)	ADDRESS	4	IOBFCHAD (0)	– FORWARD CHAIN ADDRESS
48 (30)	CHARACTER	1	IOBCOUNT	– WRITE CHECK COUNTER
49 (31)	ADDRESS	3	IOBFCHNB	– FORWARD CHAIN ADDRESS
52 (34)	ADDRESS	4	IOBBCHAD	– BACKWARD CHAIN ADDRESS
GAM EXTENSION 40 BYTES
32 (20)	CHARACTER	1	IOBUCBXG	– UCB INDEX
33 (21)	BITSTRING	3	IOBRSV37	– RESERVED
36 (24)	ADDRESS	4	IOBNXTPT (0)	– ADDRESS OF NEXT AVAILABLE IOB. SET TO ZERO IF THIS IS LAST IOB.
36 (24)	BITSTRING	1	IOBSTATA	– STATUS INDICATORS
	1. . . . . . .		IOBAVLFL	"X'80'"– IF 0, IOB IS AVAILABLE. IF 1, IOB IS NOT AVAILABLE.
	.1. . . . . .		IOBRSV20	"X'40',,C'X'"RESERVED
	. .1. . . . .		IOBRSV21	"X'20',,C'X'"RESERVED
	. . .1 . . . .		IOBRSV22	"X'10',,C'X'"RESERVED
	. . . . 1. . .		IOBRSV23	"X'08',,C'X'"RESERVED
	. . . . .1. .		IOBRSV24	"X'04',,C'X'"RESERVED
1	. . . . . .1.		IOBRSV25	"X'02',,C'X'"RESERVED
	. . . . . . .1		IOBRSV26	"X'01',,C'X'"RESERVED
37 (25)	ADDRESS	3	IOBNXTPB	– ADDRESS OF NEXT AVAILABLE IOB. SET TO ZERO IF THIS IS LAST IOB
40 (28)	CHARACTER	32	IOBCCW	– LIST OF CHANNEL COMMAND WORDS TO TRANSFER DATA
QISAM EXTENSION 2 BYTES
40 (28)	CHARACTER	2	W1IEXTEN (0)	– APPENDAGE CODES FOR BOTH NORMAL AND ABNORMAL CHANNEL END CONDITIONS
40 (28)	CHARACTER	2	W1OEXTEN	– SAME AS W1IEXTEN ABOVE
BDAM EXTENSION 40 BYTES + CHANNEL PROGRAM
40 (28)	SIGNED	2	IOBDBYTR	– NUMBER OF UNUSED BYTES REMAINING ON THE TRACK
42 (2A)	SIGNED	2	IOBDIOBS	– OVERALL SIZE OF THE IOB
44 (2C)	ADDRESS	4	IOBDPLAD (0)	– ADDRESS OF THE NEXT IOB IN THE POOL OF IOB'S
44 (2C)	BITSTRING	1	IOBDAYLI	– ALL BITS SET TO ZERO INDICATE THE AVAILABILITY OF THIS IOB
45 (2D)	ADDRESS	3	IOBDPLB	– ADDRESS OF THE NEXT IOB IN THE POOL OF IOB'S
48 (30)	BITSTRING	1	IOBDTYPE	– THE TYPE OF REQUEST AND SPECIFIED OPTIONS
	1. . . . . . .		IOBVERFY	"X'80'"– VERIFY
	.1. . . . . .		IOBOVFLO	"X'40'"– OVERFLOW
	. .1. . . . .		IOBEXTSC	"X'20'"– EXTENDED SEARCH
	. . .1 . . . .		IOBFDBCK	"X'10'"– FEEDBACK
	. . . . 1. . .		IOBACTAD	"X'08'"– ACTUAL ADDRESSING
	. . . . .1. .		IOBDYNBF	"X'04'DYNAMIC BUFFERING
	. . . . . .1.		IOBRDEXC	"X'02'"– READ EXCLUSIVE
	. . . . . . .1		IOBRELBL	"X'01'"– RELATIVE BLOCK ADDRESSING
49 (31)	BITSTRING	1	IOBDTYP2	– SECOND BYTE OF OPTIONS AND REQUESTS
	1. . . . . . .		IOBSKEY	"X'80'"– KEY ADDRESS CODED AS 'S'
	.1. . . . . .		IOBSBLKL	"X'40'"– BLOCK LENGTH CODED AS 'S'
	. .11 . . . .		IOBSUFFX	"X'30'"– IF BITS 2 AND 3 ARE ONE, RU IS SUFFIXED TO THE TYPE, INDICATING THAT THE FEEDBACK ADDRESS IN DECNXADR CAN BE THE ADDRESS OF EITHER THE NEXT DATA RECORD OR THE NEXT CAPACITY RECORD, WHICHEVER OCCURS FIRST. IF BIT 2 IS ZERO AND BIT 3 IS ONE, R IS SUFFIXED TO THE TYPE, INDICATING THAT THE FEEDBACK ADDRESS IN DECNXADR IS THE ADDRESS OF THE NEXT DATA RECORD.
	. . . . 1. . .		IOBRQUST	"X'08'"– IF 1, READ REQUEST. IF 0, WRITE REQUEST.
	. . . . .1. .		IOBTYPE	"X'04'"– IF 1, KEY TYPE. IF 0, ID TYPE.
	. . . . . .1.		IOBADDTY	"X'02'"– ADD TYPE
	. . . . . . .1		IOBRELEX	"X'01'"– RELEX MACRO ISSUED
50 (32)	CHARACTER	2	IOBDSTAT (0)	– STATUS OF THE I/O REQUEST
50 (32)	BITSTRING	1	IOBSTAT1	– FLAG BYTE
1.	1. . . . . . .		IOBABNRM	"X'80'"– ABNORMAL COMPLETION
	.1. . . . . .		IOBNEWVL	"X'40'"– ON EXTENDED SEARCH, THE NEXT EXTENT IS ON A NEW VOLUME. THE ASI ROUTINE MUST ISSUE THE EXCP MACRO. THE END–OF–EXTENT APPENDAGE CANNOT.
	. .1. . . . .		IOBSYNCH	"X'20'"– MODULE WAS ENTERED VIA SYNCH MDC037
	. . .1 . . . .		IOBPASS2	"X'10'"– ON EXTENDED SEARCH, INDICATES TO THE RELATIVE BLOCK CONVERSION ROUTINE THAT THE SECOND PASS OF A TWO-PASS CONVERSION ROUTINE HAS COMPLETED
	. . . . 1. . .		IOBENQUE	"X'08E'"– FOR EXCLUSIVE CONTROL REQUEST, INDICATES THAT A RECORD HAS BEEN ENQUEUED
	. . . . .1. .		IOBBUFF	"X'04'"– A BUFFER HAS BEEN ASSIGNED TO THIS IOB
	. . . . . .1.		IOBADDVU	"X'02'"– IOB BEING USED TO ADD A VARIABLE (V) OR UNDEFINED (U) TYPE RECORD TO THE DATA SET
	. . . . . . .1		IOBSIORT	"X'01'"– INDICATES TO THE DYNAMIC BUFFERING ROUTINE THAT IT WAS ENTERED FROM, AND IS TO RETURN TO, THE START I/O APPENDAGE MODULE
51 (33)	CHARACTER	1	IOBSTAT2	– ERROR CODE FOR ABNORMAL COMPLETION USED AS POST CODE IN ECB
52 (34)	ADDRESS	4	IOBDCPND	– ADDRESS OF LOCATION WHERE CHANNEL END PROGRAM SHOULD END
56 (38)	SIGNED	2	IOBDBYTN	– NUMBER OF BYTES NEEDED ON A TRACK TO WRITE A NEW BLOCK
58 (3A)	BITSTRING	1	IOBREQ	– REQUEST FLAGS
	1. . . . . . .		IOBREC31	"X'80'"– BLOCK REFERENCE ADDR (DECRECPT) IS A 31 BIT ADDR
	.1. . . . . .		IOBKEY31	"X'40'"– KEY ADDR (DECKYADR) IS A 31 BIT ADDR
	. .1. . . . .		IOBDAT31	"X'20'"– DATA ADDR (DECAREA) IS A 31 BIT ADDR
59 (3B)	BITSTRING	1	IOBRSV34	– RESERVED
60 (3C)	ADDRESS	4	IOBDQPTR	– ADDRESS OF IOB FOR NEXT I/O OPERATION TO BE EXECUTED
64 (40)	BITSTRING	8	IOBRSV35	– RESERVED
72 (48)	CHARACTER	8	IOBDNCRF	– COUNT FIELD FOR NEW BLOCK
80 (50)	DBL WORD	8	IOBCHNPR (0)	– CHANNEL PROGRAM USED TO TRANSFER DATA AS REQUESTED BY THE READ OR WRITE MACRO INSTRUCTION STARTS HERE