Page ()f GA22-7000-4 Revised September 1, 1975
By TNL: GN22-0498
Decimal Instructions describes in detail the in­
struetions provided by the decimal feature.
Floating-Point Instructions contains detailed de­
scriptions of the instructions provided by the
floating-point feature and by the extended-precision
floating-point feature. Alachine-Check Handling describes the Syst
1 em/370 mechanism for detecting, correcting,
and reporting machine malfunctions.
Input/Output Operations explains the programmed
control of I/O devices by the channel and by
the CPU. It includes detailed descriptions of the I/O instructions, channel command words, and other I/O control formats.
System Console describes the basic manual func­
tions and controls available for operating and con­
trolling the system.
The Appendixes include: • A list of the System/370 features • A discussion of certain functions that differ
from System/360 • Lists of the instructions arranged in several
sequences • Summaries of important formats and of condition­
code settings • Table of the powers of 2 • Tabular information helpful in dealing with hexa-
decimal numbers • An EBCDIC chart • Information about number representation • Instruction-use examples
Largely because the manual is arranged for refer­
ence purposes, certain words and phrases appear, of
necessity, earlier in the manual than the principal
discussions explaining them. The reader who en­
counters a problem of this sort should refer to the
index, which will indicate the location of the key
description.

IBM System/370 . 9
General-Purpose Design . 9
Compatibility. 10 System Program . 10 Availability 11 System Organization. 13
Main Storage . 13
Information Formats 14
Addressing 14
Information Positioning 15
Central Processing Unit. 15
General Registers 16
Floating-Point Registers 16
Control Registers 16
Input and Output 17
Channels. 17
Input/Output Interface 17
Input/Output Devices and Control Units. 18 System Console . 18
Program Execution 19
Instructions . 19
Operands. 19
Instruction Format 20 Address Generation . 21
Program Status Word 22
Instruction Execution 22
Branching. 22
Interruptions. 22
Sequence of Storage References 23
Instruction Fetch 23
DAT Table Fetches . 24
Key-in-Storage Accesses 24 Storage-Operand References 25 Storage-Operand Consistency 26
Relation Between Operand Accesses 27
Serialization . 28 System Control 29 CPU States 30 Wait and Running States 30 Problem and Supervisor States. 30 Stopped and Operating States . 30 Control Modes 31
BC Mode. 32
EC Mode. 32 Set-System-Mask Suppression 32
Program Status Word 32
Program Status Word Format in BC Mode 33
Program Status Word Format in EC Mode 34
Exceptions Associated with the PSW . 35
Control Registers 36
Key in Storage 38
Protection 38
Protection Action 38
Accesses Protected 39
Monitoring 39
Page Revised September 1, 1975
By TNL: GN22-0498 Contents
Program-Event Recording . 39
Control Register Allocation 40 Operation. 40 Storage Area Designation 42
Program Events . 42
Indication of Events Concurrently with Other Interruption Conditions 43
Direct Control 46
Time-of-Day Clock 46
Format 46 States. 46 Setting and Inspection of Value 47
Clock Comparator 47 CPU Timer 48
In terval Timer 49
Externally Initiated Functions 50 Resets. 50 Store Status . 54
Initial Program Loading. 54
Dynamic Address Translation. 57
Logical Storage Addressing. 58
Control 58 PSW 58
Control Register 0 58
Control Register 1 59
Translation Tables 59
Segment-Table Entries 59
Page-Table Entries 60 Transla tion 60 Types of Translation 60 Translation Process . 60 Addresses Translated 62
Interlocks Between Logical and Real Storage References 63
Table Manipulation . 64
Translation-Lookaside Buffer . 64 States of Translation-Table Entries 65 Use of the Translation-Lookaside Buffer . 65
Modification of Translation Tables 66
Reference and Change Recording . 67
Address-Translation Exceptions 68 Summary of Dynamic Address Translation Formats 68
Interruptions 69
Interruption Action. 70 Source Identification 70. Enabling and Disabling . 70 Instruction-Length Code 71
Point of Interruption 74
Instruction Execution 74
Machine-Check Interruption 75
Program Interruption 75
Program Interruption Conditions 75
Recognition of Access Exceptions 80 Handling of Multiple-Program-Interruption Conditions. 83
Supervisor-Call Interruption 84
External In terruption 84
Input/Output Interruption. 88
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