System Control Blocks

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Offset 16 (10) 7 17 (11) • 7 24 (18) 4 28 (le) 2 30 (lE) •• 2 30 (lE) •• 1 Bytes and Field Alignment Name 31 (IF) ••• 1 32 (20) 8 ICBSTART 1. •• • ... • xxx xxxx 32 (20) Byte 1 33 (21) Bytes 2- 8 INTERRUPTION CONTROL BLOCK Hex. Dig. Field Description, Contents, Meaning Flag byte 3. Flags for I/O supervisor error routine (device dependent) • CSW Low order seven bytes of the last CSW. Shows channel status for this request. Channel program pointer Address of the channel program to be executed. Increment amount Magnetic tape Constant that is used to increment the block count Always zero for direct access. Indicators. Special volume full indicator signifying end-of-tape mark or reflective spot sensed along with a read or write error. (Reserved Bits) Always zero • Reserved. 208 OS System Control Blocks (Release 21.7) Seek Information. This field is present for direct access devices only The number of the DEB extent to be used for this request. The first extent is number zero. The seek address for this I/O request.
Input/Output Block The input/output block (lOB) is the communication medium between a routine that requests an I/O operation and the I/O supervisor. All the information required by the I/O supervisor to execute an I/O operation is contained in the lOB, or is pointed to by the lOB. Figure 19 shows the format of the lOB. Descriptions of the fields follow the illustration. The lOB format falls into three segments whose use varies mainly by access method: Prefix -- • GAM, QISAM. • BSAM, QSAM, BPAM • BSAM, QSAM, BPAM • BDAM Standard Fields -- Normal scheduling. Chained scheduling. • Displacements 0-31 (decimal), 0-1F (hexadecimal) • Extension • BTAM. • GAM. • Direct-access storage devices. • BSAM, QSAM, BPAM. • QISAM, Scan Mode. • BISAM. • EDAM. The following illustrates the relationship of these segments. 0(0) 32 (20) Prefix Segment Standard Fields Segment Extension Segment lOB 209
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Systems Reference Library IBM Syste
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Figures Figure 1A. Pointer Diagram
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System Control Blocks System contro
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. ..J MFT Figure lA. Pointer Diagra
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Contents Directory Entry (MVT Only)
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20 OS System Control Blocks (Releas
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Offset -8 (-8) 2 Bytes and Field Al
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Offset 124 (7C) 4 128 (80) 4 132 (8
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0(0) 4 (4) 8 (8) 12 (c) 16 (10) 20
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DATA CONTROL BLOCK -- SAM Continued
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Offset 53 (35) • 3 56 (38) 1 57 (
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Device Interface 16 (10) Common Int
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Offset 16 (10) 1 11 (11) • 1 18 (
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Offset 40 (28) 8 48 (30) 1 49 (31)
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Offset Bytes and Field Alignment Na
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Device Interface 16 (10) Common Int
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WTTA Interface 16 (10) DCBBQFLG Dat
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Offset 20 (14) 1 21 (15) • 3 24 (
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Offset Bytes and Field Alignment N
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DATA CONTROL BLOCK -- TCAM The form
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Offset 33 (21) • 3 36 (24) 1 37 (
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Offset 52 (34) 1 52 (34) 4 56 (38)
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112 OS System Control Blocks (Relea
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Appendage Table DATA EXTENT BLOCK -
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offset -36 (-24) 4 -32 (-20) 4 -28
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Offset +0 +0 +0 +1 +0 +4 +8 +0 +4 +
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DATA EXTENT BLOCK -- QTAM MESSAGE P
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Offset 48 (30) 4 52 (34) 1 53 (35)
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- 36 (- 24) -32 (-20) -28 (+ lC) -2
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DATA EVENT CONTROL BLOCK -- BSAM Th
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Offset 12 (e) 4 16 (10) 4 20 (14) 4
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DATA EVENT CONTROL BLOCK -- BlSAM T
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o (0) DATA EVENT CONTROL BLOCK -- B
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DATA EVENT CONTROL BLOCK -- QTAM Th
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DATA EVENT CONTROL BLOCK -- BTAM Th
Page 157 and 158: Offset Bytes and Field Alignment Na
Page 159 and 160: Offset 28 (lC) 29 (lD) • 1 Bytes
Page 161: Device Name Table The device name t
Page 164 and 165: 164 OS System Control Blocks (Relea
Page 166 and 167: 166 05 System Control Blocks (Relea
Page 168: 10 (0) ....,r- 44 (2C) DS1FMTID For
Page 177 and 178: 72 (48) FORMAT 2 -- INDEX DATA SET
Page 179 and 180: Offset 64 (40) 2 Bytes and Alignmen
Page 181 and 182: FORMAT 3 -- EXTENSION DATA SET CONT
Page 185 and 186: Offset o (OJ 44 44 (2C) 1 45 (2D)
Page 188: ...... ---r 0(0) 4 (4) 44 (2C) DS5F
Page 191 and 192: FORMAT 6 -- SHARED EXTENT DATA SET
Page 193 and 194: Data Set Labels -- Magnetic Tape Th
Page 196 and 197: o (0) :.::: 4 (4) .,r- Continued Co
Page 198 and 199: 198 OS system Control Blocks (Relea
Page 200: 0(0) 4 (4) 16 (10) 36 (24) FL2RECFM
Page 203 and 204: Event Control Block The event contr
Page 206: INTERRUPTION CONTROL BLOCR 0(0) ICB
Page 214: Offset Bytes and Field Alignment Na
Page 220: Offset Bytes and Field Alignment Na
Page 227 and 228: Offset 68 (44) 1 70 (46) •• 2 7
Page 232: Offset 101 (65) • 1 101 (65) •
Page 238 and 239: JOB STEP CONTROL BLOCK 240 (FO) JSC
Page 240: 240 os System Control Blocks (Relea
Page 245 and 246: Offset 40 (28) 2 40 (28) 41 (29) 42
Page 253 and 254: Offset 96 (60) 1 91 (61) • 3 100
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Offset I o (0) 8 8 (8) 3 *tes and ,
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Offset Bytes and Alignment I 24 (18
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Offset Bytes and Field A1ignment Na
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REQUEST BLOCKS -- MVT CONFIGURATION
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Interruption Request Block -- MVT T
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proqram Request Block -- MVT The pr
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Offset o (0) B 8 (8) 1 9 (9) • 1
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Supervisor Request Blocks -- MVT Th
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Supervisor Request Block -- MVT --
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SUPERVISOR REQUEST BLOCK -- MVT --
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302 OS system Control Blocks (Relea
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Offset o 1 2 4 8 (0) 1 Bytes and Fi
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Bytes and Offset Alignment 105 (69)
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1-32 (20) r- L,. 0(0) 4 (4) 8 (8) 1
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Bytes and Field Offset Alignment Na
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1116 (74) 120 (78) 124 (7C) 128 (80
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Offset 31 (IF) 32 (20) Byte and Fie
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Offset 168 (AB) 4 172 (AC) 1 173 (A
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TIMING CONTROL TABLE 0(0) TCTQA 3 (
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Offset o (0) 3 Bytes and Field Alig
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Offset o 4 6 8 10 +0 (0) 4 (4) 2 By
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Offset +3 +4 +12 +15 +0 Bytes and F
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UCS 1403 Printer Extension 0(0) 4 (
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Offset 45 (2D) • 3 48 (30) 8 56 (
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Offset Bytes and Alignment 10 (A)
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MAGNETIC TAPE DEVICE CLASS UCBTYP B
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Byte 1 lOS Flogs I Model Code I UCB
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UCB + 16 (10) Offset 16 (10) 1 Byte
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ASCII Volume Header Label I 0 (0) 1
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Volume Table of Contents The volume
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Volume Table of Contents The volume
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Time-Sharing Option Control Blocks
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Driver Parameter Area The driver pa
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ENVIRONMENT CONTROL TABLE 0(0) ECTR
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Protected Step Control Block The pr
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Offset o (0) 7 Byte and Field Align
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Time-Sharing Job Block The time sha
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Indexes to system reference library
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liO coo.nter table 339 I/O lookup t
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