System Control Blocks

Offset
Bytes and Field
Alignment Name
DATA CONTROL BLOCK -- BDAM
Field Description, Contents, Meaning
ACCESS METHOD INTERFACE -- BDAM
49 (31) • 3 DCBREAD, DCBWRITE
Address of the READ/WRITE module.
52 (34) 1
53 (35) • 3
56 (38) 4
60 (3C) 2
62 (3E) •• 2
64 (40) 4
68 (44) 4
72 (48) 4
76 (4C) 4
80 (50) 1
81 (51) • 3
84 (54) 1
85 (55) • 3
88 (58) 1
89 (59) • 3
92 (5C) 4
96 (60) 4
100 (64) 4
DCBOPTCD
1 ••.
. 1 ..
. . 1.
• . . 1
1 •••
• 1 ••
• . 1.
" . .. 1
DCBCHECK
DCBSYNAD
DCBBLKSI
DCBIOBSQ
DCBSQND
DCBIOBUQ
DCBUQND
DCBLIMCT
DCBXCNT
DCBXARG
DCBMVXNO
DCBDRDX
DCBDFOR
DCBDFBK
DCBDYNB
Option Codes:
Code
W Write validity check.
Track overflow •
E Extended search •
F
A
R
Feedback •
Actual addressinq.
Dynamic buffering •
Read exclusive •
Relative clock addressing.
Address of the CHECK module, IGG019LI.
Address of SYNAD (synchronous error) routine.
Reserved.
Maximum block size.
Address of first lOB on unscheduled queue for either;
A WRITE-add request when another WRITE-add is in
progress, or a READ-exclusive request when the
READ-exclusive list is full.
Address of last lOB on unscheduled queue.
Address of the first lOB on the unposted queue.
This queue is for lOBs requesting a record already
under READ exclusive control.
Address of the last job on the unposted queue that is
maintained by the READ exclusive module.
Reserved.
Number of tracks or number of relative blocks to be
searched (extended search option).
Number of entries in the READ exclusive list.
Address of the READ exclusive list.
The total number of extents in a multivolume data
set.
Address of the READ exclusive module.
Address of a FORMAT module.
Address of a FEEDBACK module.
Dynamic buffering:
Address of the dynamic buffer module.
Unblocked spanned records with BFTEK=R specified and
no dynamic buffering:
Address of the segment work area control block.
DCB -- BDAM 81