Data Set Label Error Checking; Modify Index Mode (M); Modulus - IBM 3741 Data Station Reference Manual

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Data Set Label Error Checking
The 3741 checks to see if any of the following error condi-
tions exist in the data set label:
1. The beginning of extent address is less than track
01, sector 01.
2. The end of extent address is greater than track 74,
sector 26_
3.
4.
5.
6.
7_
The end of extent address is less than the beginning
of extent address.
The end of data address is greater than the end of
extent address plus 1.
The end of data address is greater than track 75,
sector 01.
The sector is 00 or greater than 26.
The record length is equal to 0 or greater than 128
for the 3741.
8. The third character of the record address of begin-
ning of extent, end of extent, or end of data is other
than O.
9. The last record read and currently displayed is from
track 00, sectors 1 through 7.
10. The fourth position of the header 1 field is a number
other than one.
11. The record has been deleted_
When a header 1 record in sectors 08 through 26 is read,
the 3741 checks the first eight conditions in the previous
list. If any of these conditions exist, an incorrect data set
label (8) error is displayed.
When update, verify, enter, or search mode is attempted
from the index track, all 11 conditions are checked. If
anyone of the 11 conditions is present, the incorrect data
set label (8) error is displayed.
Multiple Data Sets Per Disk
For ease of processing, one data set per disk is the best.
However, more than one data set can be on one disk. Each
data set is identified by its respective data set label on the
index track. Each data set label identifies a data set as to
its beginning and ending addresses, whether the data set
has been verified, the record length, the name of the data
set (optional field) and other information about the
data set. When a diskette is inserted into the disk drive, .
the data set label at sector 08 on the index track is always
displayed first. If there are other defined data set labels
on the index track, the operator can record advance until
the appropriate data set label is found_ To aid the operator
in reviewing and finding the desired data set label, the
data set name field (positions 6-13) in the data set label
should be used. In addition, the data set label creation
date field and the data set expiration date field should also
be used when a clear distinction between jobs is needed to
ensure the selection of the correct data set. Then in addi-
tion to reading the data set name, the operator could also
check the creation and expiration dates to ensure proces-
sing of the right data set, or the right version of the data
set.
Modify Index Mode (M)
The modify index mode is used to modify records on the
index track. Fields in a data set label, new data set labels,
the volume label, or other records on the index track can
be modified by using the modify index mode. Any of the
records can also be deleted with the use of the modify
index mode function_
To perform a modify index function, record backspace or
record advance to get to the appropriate index track
record to be modified, key the record to be written, then
select modify by pressing. FUNCT SEL lower and M. The
modify mode can be selected from the read index mode
.only; if it is selected from another mode, a mode selection
(M) error occurs. No other mode can be selected from the·
modify mode.
DELET~
REC, RESET, and REC ADV
are the only valid keys in the modify mode. All others
give a function not available (F) error. The mode reverts
to read index after the first keystroke following the
selection of modify mode.
Operation Modes and Considerations 11