Virtual Storage And Dynamic Address Translation; Virtual Storage Concepts, Advantages, And Terminology; The Need For Larger Address Space - IBM System/370 145 Manual

SECTION 15: VIRTUAL STORAGE AND DYNAMIC ADDRESS TRANSLATION
The first subsection, 15:05, discusses the needs that virtual storage
and dynamic address translation in System/310 are designed to address.
No previous understanding of these facilities is assumed,. In this
discussion, an address space is defined as a consecutive set of
addresses that can be used in programs to reference data and
instructions. System operation in IBM-suppo:rted virtual storage
environments is explained conceptually, without use of all the
terminology new to such an environment.
The general advantages of IBM-supplied vi.rtual storage operating
systems are presented also. Included in this subsection are those that
apply to DOS/VS, OS/VS1. and OS/VS2. Additional advantages of virtual
storage that are specific to a particular IBM-supplied operating system
are discussed in the optional supplement for that operating system.
The last portion of subsection 15:05 defines the terminology
associated with virtual storage and dynamic address translation
hardware. The terminology included is that common to the IBM-supplied
operating systems that support a virtual storage environment for
System/310. Terms unique to a particular operating system are defined
in the optional supplement that describes that operating system.
subsection 15:10 describes in detail the implementation and operation
of dynamic address translation and channel indirect data addressing in
the Model 145. Other hardware items associated with dynamic address
translation, such as reference and change recording, are discussed also.
The last-subsection, 15:15, discusses the new factors that affect
system performance in a virtual storage environment. The information
present is related to the efficient installation and utilization of an
IBM-supplied virtual storage operating system.
The optional programming systems supplements (Sections 80 to 110)
assume knowledge of the entire contents of Section 15.
15:05 VIRTUAL STORAGE CONCEPTS, ADVANTAGES, AND TERMINOLOGY
THE NEED FOR LARGER ADDRESS SPACE
The past and present rapid growth in the number and types of data
processing applications being installed has led to an increasing demand
for more freedom to design applications without being concerned about,
or functionally constrained by. the physical characteristics of a
particular computer system--system architecture, I/O device types, and
processor storage size. As program design and implementation become
easier, they can enable more rapid installation of applications so that
the benefits of data processing can be achieved sooner.
The design of System/360 and OS MFT and MVT allowed programmers to be
less concerned than before about specific CPU architecture and I/O
device types when designing and implementing applications by (1)
providing a compatible set of CPU models ranging in size from small to
large scale, (2) providing a variety of high-level languages with
greatly expanded capabilities, including a new language (PL/I), (3)
providing comprehensive data management functions, including support of
I/O device independence where data organizat.ion and the physical
characteristics of devices permitted, and (4) supporting dynamic
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A
Guide to the IBM System/310 Model 145