IBM System/370 145 Manual page 55

allocation of system resources (channels, I/O devices, direct access
space, and processor storage). System/360 users who installed DOS
Version 3 also experienced more :system configuration independence than
was previously available, although to a lesser degree than OS MFT and
MVT users.
While System/360 and its primary operating systems represented major
steps toward giving programmers 4a larger measure of system configuration
independence, constraints that. r,esulted from the necessity to design
applications to fit within the alnDunt of processor storage available
still existed. In addition, although System/360 models provided more,
less costly processor storage tban was previously available,
increasingly larger amounts of p:['ocessor storage began to be required
as
the use of high-level languages increased, the usage and level of
multiprogranuning increased, the :functions supported by operating system
control programs expanded, and applications that require relatively
larger amounts of processor storage (such as teleprocessing and data
base) were designed and installed. more frequently.
The requirement for moreproc~essor storage is still growing. The new
applications being developed and installed tend to have larger and
larger storage design points in order to provide the fUnctions desired.
More processor storage is also
r~equired
for
I/O
buffer areas to aChieve
maximum capacity and performance for sequential operations using new
System/370 direct access devices with significantly larger track
capacities. Larger blocking of 1tape records, which r~uires larger I/O
buffers, also results in increas~~d tape reel capacity and decreased tape
processing time. As a result, S~~stem/370 models provide significantly
more processor storage than theill:' predecessor system/360 models and
offer it for lower cost.
The availabil ity of more proc.:!ssor storage, however, has not relieved
all the constraints associated with processor storage. Applications
still must be tailored to the amount of processor storage actually
available in a given system 'even though storage design points (paritition
and region sizes) can
be
larger 1:han they were previously.
Consider the following s:ituations that can occur in installations:
1. An application is designed to operate in a 50K processor storage
area that is adequate to handle current processing needs and that
provides room for some e~)ansion. Some time after the
application is installed, however, maintenance changes and the
addition of new functions cause one of the programs in the
application to require
sue
and another to require 52K.
Installation of the next processor storage increment cannot be
justified on the basis of these two programs so time must be
spent restructuring and rE~testing the programs to fit within 50K.
2.
An
existing application has programs with a planned overlay
structure. The volume of transactions processed
by
these
programs has doubled and better performance is now required.
Additional processor storage is installed. However, the overlay
programs cannot automatically use the additional storage.
Therefore, reworking of the overlay programs is required to take
them out of planned overlzLY structure and, thereby, achieve the
better performancE;! desired.
3. A low-volume, terminal-oriented, simple inquiry program that will
operate for three hours a day is to be installed. If the program
is written without any type of overlay structure, it will require
60K of processor storage t:o handle all the various types of
inquir~es. However, becau~e of a low inquiry rate, only 8K to
12K of the total program tArill
be
active at any given time. In
order to justify its operaLtional cost, considerable additional
A Guide to the IBM System/370 Modlel 145 45