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Offset<br />
16 (10) 1<br />
17 (11) • 3<br />
20 (14) 1<br />
21 (15) • 3<br />
24 (18) 2<br />
26 (lA) •• 2<br />
26 (lA)<br />
27 (lB)<br />
28 (lC) 4<br />
Bytes and Field<br />
Alignment Name<br />
DCBKEYLE<br />
DCBREL<br />
DCBBUFNO<br />
DCBBUFCB<br />
DCBBUFL<br />
DCBDSORG<br />
Byte 1<br />
xx.x xxx.<br />
•• 1. ••• 1<br />
Byte 2<br />
DCBIOBAD<br />
DATA CONTROL BLOCK -- BDAM<br />
Field Description, Contents, Meaning<br />
DEVICE INTERFACE<br />
Key length.<br />
Number of relative tracks or blocks in this data set.<br />
COMMON INTERFACE<br />
Number of buffers required for this data set.<br />
May range from 0 to 255. If unblocked spanned<br />
records are used, the number of segment work areas<br />
required for this data set.<br />
Address of buffer pool control block or of dynamic<br />
buffer pool control block.<br />
Length of buffer. May range from 0 to 32,767.<br />
Data set organization being used.<br />
(Reserved bits)<br />
DA Direct organization •<br />
U Unmovable - the data contains location dependent<br />
information.<br />
Reserved.<br />
Address of the standard fields of the first lOB in<br />
the pool of lOBS.<br />
FOUNDATION EXTENSION<br />
32 (20) 1 DCBHIARC, DCBBFTEK, DCBBFALN<br />
x... .x ..<br />
0 •••• 0 ••<br />
o. .. .1 ••<br />
1. •. .0 ••<br />
• • x.<br />
.. 1.<br />
78 OS <strong>System</strong> <strong>Control</strong> <strong>Blocks</strong> (Release 21.7)<br />
Buffer pool location, coded in the DCB macro<br />
instruction:<br />
Before OPEN -<br />
none No choice made in the DCB macro instruction.<br />
After OPEN -<br />
If no choice is made in the DD statement either<br />
(as shown by the JFCBHIAR field), the OPEN<br />
routine resets these two bits from 00 to 01.<br />
o Hierarchy 0 main storage.<br />
(See also: After OPEN, above.)<br />
1 Hierarchy 1 main storage.<br />
R<br />
Buffering technique •<br />
Unblocked spanned records:<br />
Software track overflow. OPEN forms a segment<br />
work area pool. (However, see bit 51.7). The<br />
number of segment work areas is determined by<br />
DCBBUFNO (offset: 20). OPEN stores the address<br />
of the segment work area control block in<br />
DCBDYNB (offset 100) if dynamic buffering is not<br />
used, or in the dynamic buffer pool control<br />
block (see DCBBUFCB, offset 21) if dynamic<br />
buffering is used. WRITE uses a segment work<br />
area to write a record as one or more segments.<br />
READ uses a segment work area to read a record<br />
that was written as one or more segments.
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