System Control Blocks

Offset
Bytes and Field
Alignment Name
DATA CONTROL BLOCK -- ISAM
Hex.
Dig. Field Description, Contents, Meaning
FOUNDATION EXTENSION
32 (20) 1 DCBHIARC, DCBBFTEK, DCBBFALN
33 (21) • 3
36 (24) 1
31 (25) • 3
x. •• .x ••
0 •••• 0 ••
o. .. .1 ..
1. •• • O ••
.xxx x •••
• .xx
• .10
• .01
• .11
DCBEODAD
DCBRECFM
10 ••
01 ••
11 ••
• . 1.
••• 1
1 •••
• 10.
• 01.
• 00.
••• 1
DCBEXLST
Buffer pool location, coded in the DCB macro
instruction:
Before OPEN -
none No choice made in the DCB macro instruction.
After OPEN -
If no choice is made in the DD statement either
(as shown by the JFCBHIAR field), the OPEN
routine resets these two bits from 00 to 01.
o Hierarchy 0 main storage.
(See also: After OPEN, above.)
1 Hierarchy 1 main storage.
(Res erved bits)
Buffer alignment:
D Doubleword boundary.
F FUllword not a doubleword boundary, coded in the
DCB macro instruction.
F FUllword·not a doubleword boundary, coded in the
DD statement.
Address of a user-provided routine to handle
end-of-data conditions.
Record format.
Code
-F-
V
U
T
B
S
A
M
Fixed length records.
Variable length records.
Undefined length records.
Track overflow •
Blocked records •
may not occur with undefined (U).
Standard records. No truncated blocks or
unfilled tracks are embedded in the data set.
ASA control character •
Machine control character •
No control character •
Key length (KEYLEN) was specified in the DeB
macro instruction; this bit is inspected by the
open routine to prevent overriding a
specification of KEYLEN=O by a non-zero
specification in the JFCB or data set label.
Exit List. Address of a user-provided list.
DCB -- ISAM 61