IBM 1130 User Manual page 128

Section
Subsections Page
20 40
I
20 01
Field Size
The number of positions required to record each item
of information should be determined and entered on
a form similar to that shown in Figure 20. 1.
Type of Field
Control and indicative data field size should equal
the total number of digits in the largest single item
to be recorded in the particular field. Occas ionally,
to conserve storage, the high-order digits may be
disregarded for a field such as order number.
Quantitative data field size may equal the total
number of digits in the largest amount to be recorded,
or the number of digits that will occur with reason-
able frequency. Procedures can be developed to
handle the rare exceptions.
Recording Medium
Since some media, such as cards and disks, contain
a fixed number of positions per unit of storage (card
field or disk sector or track, etc.), it is essential
to consider this overall limit in order to design
efficient and practical records.
Example:
On the 1130, your disk records are automatically
Itblocked lt within 320-word sectors. A 55-word
record will be blocked 5 records to the sector
with 320-(5x55) or 45 words unused. Rather than
waste these 45 words, you might as well increase
the size of the record to 64 words, which will
still allow 5 per sector (5x64
=
320) with
~
waste. Or, if possible, reduce the record size
to 53 words, which permits 6 records per sector.
File Size (Total Number of Records)
Since the field size affects the total record siz"e, all
unnecessary positions should be eliminated to de-
crease I/O time and storage media requirements.
Future Requirements
If the demands to be placed on the information ind i-
cate an impending need for another position, it
would be easier to incorporate the additional charac-
ter in the design phase so as to avoid reprogramming
and a patched -up record layout.
Field Compaction Techniques
Because a reduction in the length of a record pro-
duces such positive results as an increase in DASD
packing and a decrease in time to read and/or write,
field compaction techniques should be investigated
and the cost of the technique evaluated as each file
is designed. Some methods to consider for reducing
the number of positions are found in 80.60.00.
A given compaction technique must be evaluated
for:
1. Amount of core storage required to hold the
encode-decode instructions
2. Encode-decode subroutine timing requirements
3. Compaction percentage achieved
4. Compatibility with programm ing systems
5. Retention of collating sequence
6. Retention of fixed field length
7. Effect on the overall system, including re-
lated clerical functions
Some of these methods are discussed in detail in
section 80. For a discussion in depth of compaction
techniques see Record Compaction Techniques
(E20-8252) .