General Advantages Offered By Ibm Operating Systems That Support Avirtual Storage Environment - IBM System/370 145 Manual

a program for satisfactory operation frequently can be less than its
total storage requirement. This fact can enable an operating system to
efficiently support a virtual storage that is larger than the real
storage actually present in the computing system.
A virtual storage environment, therefore, enables most programs to be
independent of real storage size to a large degree. A program can
execute in varying amounts of dynamically available real storage without
being modified. The amount of real storage dynamically available to a
program during its execution primarily affects its performance, to the
extent that program section transfer activity is affected, rather than
its capability to be executed. For example, a given 150K language
translator might be able to operate with an average of 75K of real
storage dynamically available to it during its operation: however, the
time required to compile a program on an intermediate-scale model under
these conditions might be unacceptable. Alternatively, the performance
desired on the intermediate-scale CPU might be achieved if an average of
lOOK
is dynamically available to the language translator while it
operates. Without a virtual storage operating system, the 150K language
translator probably could not be used at all on the intermediate-scale
model because of its relatively large design point size.
The availability of lower cost real storage for the Model 145 and the
real storage independence that a virtual storage environment offers
provide new flexibility in tradeoffs among real storage cost, function,
and individual or total system performance.
GENERAL ADVANTAGES OFFERED BY IBM OPERATING SYSTEMS THAT SUPPORT A
VIRTUAL STORAGE ENVIRONMENT
Each of the IBM operating systems that supports a virtual storage
environment for System/370 models using dplamic address translation
offers the capability of using address space that is larger than that
provided by available real storage, and each supports dynamic real
storage management that is transparent to the user. As a result, these
operating systems offer certain general potential advantages that do not
depend on their unique features. The implementation of virtual storage
also provides benefits that are specific to each of these operating
systems because of their design and the particular functions they
support. The following discusses the potential advantages of virtual
storage and dynamic address translation that are common to DOS/VS,
OS/VS1, and OS/VS2 environments.
The general advantages of virtual storage operating systems are the
potential they offer for:
• Increased application development
• Expanded operational flexibility
• System performance improvement
A
virtual storage operating system can facilitate more rapid
development of new applications because,
by
removing most existing real
storage restraints on application design, it can help improve the
productivity of programmers. Specifically, a virtual storage operating
system has characteristics that can be used to reduce the effort, time,
and cost associated with application design, coding, testing, and
maintenance. This makes the installation of new applications more
readily justifiable and encourages the addition of new functions to
existing applications. The potential advantage of improved operational
flexibility is made possible by the greater independence of applications
from real storage size. Enhanced system performance can result from
improved real storage utilization. While these latter two benefits have
54 A Guide to the IBM System/370 Model 145