The 51-year History and Evolution of the z/OS Operating System FROM OS360 TO Z/OS Mark Pickett Collabera

Contents  The IBM System 360  Compact Instruction Set  The Latest Instruction Set  Virtual Memory Operating Systems  EBCDIC  Registers  PSW and Addressing Memory

The IBM System 360  System/360 core storage memory capacity ranges from 8,000 characters of information to more than 8,000,000.(IBM Archive 1964) 8 Megabytes WOW.(IBM Archive 1964)  Hundreds of terminal devices can communicate simultaneously with a system while the computer continues to process the basic job on which it is working..(IBM Archive 1964).(IBM Archive 1964)  Memory was a precious commodity. Packed Decimal was used extensively, as well as 2-digit year fields. Wikipedia ArticleWikipedia Article  Program-controlled code overlays  51 Year-old technology.

Compact Instruction Set  16-byte, 32-byte and 64-byte operations (Refers to the length of the operation code  RR Format  RX Format  RS Format  SI Format  SS Format  System 360 Principles of Operation (Bitsavers.com)(Bitsavers.com)

The Latest Instruction Set  Huge Instruction set  Includes Hyperspace and USS Instrucions  z/Architecture Principles of Operation 1568 pages (IBM Publication)(IBM Publication)

Virtual Memory Operating Systems  z/OS  z/VM  z/VSE  z/Linux

EBCDIC  Extended Binary Coded Decimal Interchange Code  This is the collating sequence and character code o the z/OS system  The instruction codes in memory (and hence in system dumps) are coded in EBCDIC  Listed in Appendix I of the z/Archtecture Principles of Operationthe z/Archtecture Principles of Operation

Registers  In the z/Architecture Principles of Operationz/Architecture Principles of Operation  General Registers  Floating-Point Registers  Floating-Point-Control Register  Control Registers  Access Registers

PSW and Addressing Memory  Program Status Word  Current State of the Processor  The FIRST thing you look for in a storage dump  It is Full of Meaningful Information, Including the Address of the Last or Current Instruction Executed  The PSW Will Tell You If the Instruction is in Real or Extended Memory  Chapter 9 in z/OS Diagnostic Data Collection and Analysisz/OS Diagnostic Data Collection and Analysis  Handy Tool, PSW Parser.xlsx

References  03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PR360.html 03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PR360.html   0_360PrincOps.pdf 0_360PrincOps.pdf 