IBM System/370 145 Manual page 66

additional real storage required can be added to the system. I~
some cases i t may be possible to operate the application on a
production basis on the existing system without adding real storage
initially, because during the startup period, transaction volume is
very low. As the volume grows, real storage can
be
added to achieve
better performance.
• Growth of existing applications and the maintenance of operational
programs is simplified.
Because of the removal of most real storage restraints, new
functions can be more easily and more rapidly added to most existing
applications. Program expansion because of added functfons or
maintenance changes does not require the use of overlay techniques,
multiple job steps, etc., when the size of the extended program
exceeds the original storage design point $ize.
In general, alteration and debugging of nonoverlay programs are also
easier than alteration and debugging of programs with planned
overlay or dynamic structures.
• Application programs whose real storage requirements, based on
transaction volume and complexity, vary widely during their
execution may be justified, designed, and installed more easily.
Design, coding, and testing time can be reduced because dynamiC
storage management is automatically provided by the operating
system. Time and effort need not be spent structuring such programs
to use available real storage dynamically to support the functions
and/or response times required.
• Design and installation of one-time, low-usage, or low-volume
programs of very large storage size are more easily justified.
Existing applications in these categories that currently operate in
a batch environment can also more easily be altered to operate
online, a grow·th step that might not be justifiable in a nonvirtual
storage environment.
• Applications can be installed on a trial basis for the purpose of
observing and evaluating their functions and their operation.
Most IBM-supplied appl.ication program products can be temporarily
installed on an existing system, assuming the required I/O devices
are present. The additional hardware resources that may be required
to operate the application on a production basis can be added later,
when the application is permanently installed.
• The benefits of the functions provided
by
many IBM-supplied
application program products with larger storage design points can
be realized using smaller System/310 models with relatively smaller
amounts of available real storage.
Currently, i t may be difficult to justify the real storage required
to install a relatively large storage desigp point application on a
smaller scale system to handle a low volume of transactions, even
though the functions provided by the application are very desirable.
In a virtual storage environment, such an application can execute
using that amount of dynamically available real storage required to
satisfy the desired performance requirements for the low volume of
activity.
Potential for Additional Operational Flexibility
The reduction of real storage restraints makes most applications more
independent of the real storage size of a system configuration and
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145