Editing IBM System/370 (section)

===Initial models===
When the first System/370 machines, the [[IBM System/370 Model 155|Model 155]] and the [[IBM System/370 Model 165|Model 165]], were introduced, the System/370 architecture was described as an extension, but not a redesign, of IBM's System/360 architecture which was introduced in 1964.<ref name="Model-165-IBM-Archives">{{cite web|url=https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3165.html|title=System/370 Model 165|website=IBM Archives|date=23 January 2003|publisher=IBM|archive-url=https://web.archive.org/web/20230729090329/https://www.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP3165.html|archive-date=2023-07-29|url-status=dead}}</ref> The System/370 architecture incorporated only a small number of changes to the System/360 architecture. These changes included:{{sfn|S370-1st|loc=[http://bitsavers.org/pdf/ibm/370/princOps/GA22-7000-0_370_Principles_Of_Operation_Jun70.pdf#page=5 Modifications to System/360]|pp=2-5}}
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* 13 new instructions, among which were
:* MOVE LONG ('''MVCL''');{{sfn|S370-1st|loc=[http://www.bitsavers.org/pdf/ibm/370/princOps/GA22-7000-0_370_Principles_Of_Operation_Jun70.pdf#page=23 Move Long]|pp=23-25}}
:* COMPARE LOGICAL LONG ('''CLCL''');{{sfn|S370-1st|loc=[http://www.bitsavers.org/pdf/ibm/370/princOps/GA22-7000-0_370_Principles_Of_Operation_Jun70.pdf#page=21 Compare Logical Long]|pp=21-22}}
::: thereby permitting operations on up to 2^24-1 bytes (16 MB), vs. the 256-byte limits on the 360's MVC and CLC;<ref>{{cite web|url=http://faculty.cs.niu.edu/~byrnes/csci360/notes/360ex.htm|title=Move Character Long|work=CSCI 360 Computer Programming in the Assembler Language}}</ref><ref>{{cite book|chapter-url=http://research.microsoft.com/en-us/um/people/gbell/tcmwebpage/timeline/chap51_ibm370_cs2.pdf|chapter=Architecture of the IBM System/370|first1=Richard P.|last1=Case|first2=Andris|last2=Padegs|title=Computer Structures: Readings and Examples|editor-first1=C. Gordon|editor-last1=Bell|editor-link1=Gordon Bell|editor-first2=Allen|editor-last2=Newell|editor-link2=Allen Newell}}</ref>
:* SHIFT AND ROUND DECIMAL ('''SRP'''),{{sfn|S370-1st|loc=[http://www.bitsavers.org/pdf/ibm/370/princOps/GA22-7000-0_370_Principles_Of_Operation_Jun70.pdf#page=25 Shift and Round Decimal]|pp=25-26}} which multiplied or divided a [[packed decimal]] value by a power of 10, rounding the result when dividing;

* optional 128-bit ([[IBM hexadecimal floating-point|hexadecimal]]) [[floating-point arithmetic]], introduced in the [[IBM System/360 Model 85|System/360 Model 85]]<ref>{{cite web|url=http://ed-thelen.org/comp-hist/IBM-ProdAnn/370-155.pdf|title=Announcing: System/370 Model 155|publisher=IBM}}</ref><ref>{{cite web|url=http://ed-thelen.org/comp-hist/IBM-ProdAnn/370-165.pdf|title=Announcing System/370 Model 165|publisher=IBM}}</ref>
* a new higher-resolution time-of-day clock{{sfn|S370-1st|loc=[http://www.bitsavers.org/pdf/ibm/370/princOps/GA22-7000-0_370_Principles_Of_Operation_Jun70.pdf#page=6 Time-Of_Day Clock]|p=6}}
* support for the block multiplexer channel{{sfn|S370
|loc=[http://bitsavers.org/pdf/ibm/370/princOps/GA22-7000-10_370_Principles_of_Operation_Sep87.pdf#page=355 Types of Channels]
|pp=13-4-13-5}} introduced in the System/360 Model 85.<ref>{{cite journal|url=http://research.microsoft.com/en-us/um/people/gbell/tcmwebpage/timeline/chap51_ibm370_cs2.pdf|title=Architecture of the IBM System/370|author1=Richard P. Case|author2=Andris Padegs|journal=[[Communications of the ACM]]|volume=21|issue=1|date=January 1978|pages=73–96|doi=10.1145/359327.359337|s2cid=207581262|quote=The IBM 2880 Block-Multiplexer Channel included most of the System/370 I/O architecture extensions and was made available on System/360 Models 85 and 195.}}</ref>
* All of the emulator features were designed to run under the control of the standard operating systems. IBM documented the S/370 [[emulator]] programs as integrated emulators.

These models had [[core memory]] and did not include support for [[virtual memory|virtual storage]], as they lacked a [[Memory management unit|DAT (Dynamic Address Translation) box]]