Chapter 1. Introduction; The Ibm 4300 Processors - IBM 4300 Manual

Chapter 1. Introduction
Contents
The IBM 4300 Processors 1-1
Compatibility 1-2
Compatibility Among 4300 Processors 1-2
Compatibility Between 4300 Processors and
System/370 1-2
Control-Program Compatibility 1-2
Problem-State Compatibility 1-2
The IBM 4300 Processors
The IBM 4300 Processors are small and moderately
sized processors that have evolved from
System/370. They may be used in one of two
architectural modes of operation. When operating
in the Extended Control Program Support: Virtual
Storage Extended (ECPS:VSE) mode, a processor
provides new facilities that are designed specifically
to enhance the DOS/VSE control program. To run
control programs such as VM/370 and OS/VS1,
which do not use these facilities, a processor is
placed in the System/370 mode. This publication
describes the architecture of the 4300 Processors
when operating in the ECPS: VSE mode.
The architecture of a machine defines its
attributes as seen by the programmer, that is, the
conceptual structure and functional behavior of the
machine, as distinct from the organization of the
data flow, the logical design, the physical design,
and the performance of any particular
implementation. Several dissimilar machine
implementations may conform to a single
architecture. When programs running on different
machine implementations produce the results that
are defined by a single architecture, the
implementations are considered to be compatible.
The ECPS:VSE mode includes a new
storage-control facility, called one-level addressing,
for creating a single virtual storage of up to
16,777,216 bytes, which both the CPU and the
channels address directly using one uniform set of
virtual addresses. Mapping the virtual storage onto
the real storage is performed internal to the
machine.
The one-level-addressing facility provides new
instructions and interruptions which the control
program uses to determine which parts of virtual
storage currently are mapped onto real storage and
thereby are made addressable. These instructions
and interruptions, and the associated internal
address-mapping functions, take the place of
dynamic address translation (DAT) and channel
indirect data addressing in System/370.
The ECPS: VSE mode also includes a new
status-saving function, called machine save, which
preserves the entire CPU state and the first 2,048
(2K) bytes of storage. The operator uses machine
save in preparation for a complete storage dump.
Machine save replaces the store-status function of
System/370, which necessarily alters some of the
storage to be dumped.
If mUltiple virtual storages are not required, the
ECPS: VSE mode affords the following advantages
w.hen compared to System/370:
• Simpler storage-mapping function, with more of
the function performed automatically by the
machine
• Improved control-program performance, because
the control program need not translate the
virtual addresses of channel programs
Programming of the machine has been simplified,
relative to System/370, by omitting the following
functions:
• Multiprocessing and associated instructions
• Machine-check logout and full channel logout
These model-dependent logouts are replaced by
internal facilities for diagnosing machine
malfunctions. This removes model-dependent
error-handling procedures from the control program
and improves serviceability.
Chapter 1. Introduction 1-1