IBM System/370 145 Manual page 67

permits most applications to
be p]~ocessed
on systems with varying
amounts of available real storage without program modification. Dynamic
real storage management reduces tile amount of job stream and operations
preplanning that is normally done toase real storage as efficiently as
possible in a multiprogramming enlrironment. The following benefits can
result:
• A system can back up another ~;ystem even though i t has less real
storage than the· system. i t ba(:ks up.
A smaller scale system with tile appropriate I/O configuration can
provide backup for a larger s(3le system if necessary.. (Performance
experienced on'the
backUP:
sys1~m may vary from that normally
achieved, depending on the two system configurations involved ..
>
• A single design and one opera1:ing procedure can
be
used for an
application that is to operatE~ on multiple systems with varying
amounts of real storage as 10J:lg as the virtual storage required is
supported by all the systems. .
When data processing is decentralized a~ng multiple installations
with systems that have differEmt amounts of real storage, one
location can design. implement:. and maintain an application that can
be used by other insta1latio~;. Duplication of this type of effort
can be minimized or eliminatecil.
• Most applications can be testEd on systems with less real storage
than the one on which they wi].1 run in a production environment, as
long as the required amount of: virtual storage is supported.
• Growth to a larger rea1
stora~re
configuration can
be
easier.
Real storage can be added to an existing system to improve system
performance (by the reduction of program section transfer activity)
without the necessity of modif:ying existing application programs so
that they can take advantage of additional real storage. Additional
real storage (up to a maximum of their design point size) is
automatically used by prograom: that operate in a virtual storage
environment.
• operators need not perforta cer:'tain procedures that are solely
related to efficiently manaqilllg real storage.
The operator is concerned'priRarily with the division of virtual
storage and therefore need not, change partition sizes at various
times (in DOS/VS or OS/vS1.
f~~
example) for the purpose of making
storage available for larger than average jobs.
(An
installation
can define virtua1 storage pcu:'titions that are larger than those
currently defined in the
nos
~~rsion 4 or OS MFT environment, and
the partitions can
be
made bigr enough to contain the largest
existing or currently planned storage design point programs.)
Similarly, in an OS/VS2 environment. the operator no longer need
start long running jobs at CeI:'tain points in time to ensure that
available real storage is;fra9~nted as little as possible.
• Priority jobs whose need to be! processed cannot be predicted can be
scheduled when required.
A nonvirtual storage enviroDJDe!nt does not provide the capability of
effectively handling the schednliJ:lg of high-priority jobs on a
random basis. Hence. this type of job is not permitted to exist in
an installation, or such jobs must be schedu1ed to operate only at
certain times. In a virt~l storage environment, a high-priority
virtual partition (in OOS/VS a,nd
os/VS1)
can
be
defined and reserved
for the purpose of processing only high-priority jobs. Except for
A Guide to the IBM System/370 MOdel. 145 57