File Numbel: 8360-36 Form C28-6535-0 Systems Reference Library IBM Operating System/360 Concepts and Facilities This publication describes the basic concepts of Operating System/360 and guides the programmer in the use of its various facilities. Operating System/360 is a comprehensive set of language translators and service programs, operating under the supervisory control and coordination of an integrated control program. It is designed for use with Groups 30, 40, 50, 60, 62, 70, and 92 of Computing System/360. It assists the programmer by extending the performance and application of the computing system. PREFACE This publication introduces and interre­ The publication is divided into two lates all Operating System/360 control pro­ parts, an introduction and survey, and a gram facilities. It shows how these facil­ detailed description. The first part con­ ities work with the language translators tains a general description of subjects of and service programs, so the programmer can interest to all users. The second part, better learn to use the system. It also meant for programmers, is a more thorough directs the programmer to related Operating discussion of the same topics. System/360 publications for specific details. Even though many details are expressed in assembler language terminology, this Many combinations of programming facili­ publication is addressed to every program­ ties are possible with Operating mer who will use System/360, and familiari­ System/360. The programmer will work with ty ~ith the assembler language is not a a particular set of these facilities, requirement. depending on the language he uses (FORTRAN, COBOL, Report Program Generator, Assembler, or New Programming Language), and the modu­ PREREQUISITE PUBLICATION: IBM Operating lar programs chosen when his operating System/360: Introduction. This publication system is generated. Although all the describes the general organization, func­ control program facilities are described tion, and application of the operating herein, all of them may not be included in system. It also describes the other relat­ every installation. ed Operating System/360 publications. This publication was prepared for production using an IBM computer to update the text and to control the page and line format. Page impressions for photo-offset printing were obtained from an IBM 1403 Printer using a special print chain. Copies of this and other IBM publications can be cbtained through IBM Branch Offices. A form for readers' comments appears at the back of this publication. It may be mailed directly to IEM. Address any additional comments concerning this publication to the IBM Corporation, programming Systems publications, Department D58, PO Box 390, Poughkeepsie, N. Y. 12602 ©1965 by International Business Machines Corporation CONTENTS PART I: INTRODUCTION AND SURVEY •• 7 Blocking and Buffering Facilities 29 Block Formats • • • • • 29 SECTION 1: INTRODUCTION. 8 Buffering Facilities •••••• 30 Buffer Pools •••••••••• 30 Elements of the Ope:r:ating System 8 Buffer Assignment Techniques and Transmittal Modes 30 Benefits to the Programmer 8 ! The Data Control Block 33 SECTION 2: SURVEY 10 OPEN and CLOSE Macro-Instructions 33 Data Access Routines • • • • •• 34 Data Management • 10 Identifying and Locating Data 10 SECTION 4: PROGRAM DESIGN AND Organizing Data •••• 11 PREPARATION ••• • 39 Storing and Retrieving Data • • • • 11 Device Independence • • • • • 12 Program Segmentation 39 Program Design and Preparation 13 Program Structures 39 programs and Subprograms • 13 Simple Structures •••• 40 Combining Subprograms 13 Deferred Exits 41 Planned OVerlay Structures 42 Job Management ••••• 15 Dynamic Serial Structures 43 Job Control ••••• 15 Link Macro-Instruction 43 The Input Job Stream • 15 Transfer Control (XCTL) Job Scheduler •••••••• 16 Macro-Instruction 44 Sequential Scheduling System 16 LOAD Macro-Instruction 45 Priority Scheduling Systems 17 Planned Overlay versus Dynamic Structures • • • • • • • • 46 Task Management • 18 Dynamic Parallel Structures • • • • 46 PART II: DETAILED DESCRIPTION 21 Program Design Facilities • • • • 47 Reusability ••••• • • • • 47 SECTION 3: DATA MANAGEMENT 22 Design of Reenterable Programs 48 Checkpoint and Restart • • 49 Data Set Identification and Extent Timer •• • • • • 49 Control ••••••• • • • • 22 Direct-Access Volume Identification Debugging Facilities 50 and the Volume Table of Contents 22 Assembler Language Program Magnetic Tape Volumes ••••••• 22 Debugging: Test Translator 50 Cataloging and Library Management 23 Test Output ••••• 51 Control Volumes • • • • • • • 24 Generation Data Groups ••••• 24 SECTION 5: JOB MANAGEMENT 52 Password Protection of Data Sets • • 25 Editing of Space, Indexes, and Control Statement Capabilities 52 Catalogs •••• 25 Scheduling Controls 53 Job Priority 53 Data Access Methods • 25 Dependencies 53 The Access Methods • • 26 Maximum Execution Time 53 Queued Sequential Access Method Non-Setup Jobs •••• 53 (QSAM) • • • • • • • • • • 26 Job Log • • • • • 54 Basic Sequential Access Method Program Source Selection • 54 (BSAM) • • • • • • • • • • • • • 26 Data Set Identification And Basic Partitioned Access Method Disposition • • • • • • • • • 54 (BPAM) • • • • • • • • • • • • • 26 SYSIN and the DD * Statement 55 Indexed Sequential Access Methods Concatenated Data Sets 55 - Basic and Queued (BISAM and Generation Data Groups 55 QISAM) • • • • • • • • • • • • • 26 Dummy Data Sets • • • • 55 Basic Direct~Access Method (BDAM) 27 Data Set Disposition • • • • 56 Queued Telecommunications Access Input/Output Device Allocation 56 Method (QTAM) ••••••••• 27 Deferred Mounting of Tapes 58 Basic Telecommunica.tions Access Direct-Access Storage Space Method (BTAM) ••••••••• 29 Allocation ••••• • • • • • 58 Cataloged pr9cedures • • • • • • •• 58 Passing And Sharing Of Main Storage Job Scheduler and Master Scheduler Areas • • • • • • • • • • • • 75 Functions • • • • • • • • • • • 58 Task Priorities And Roll-Out • 76 Job Scheduler •••• 59 Reader/Interpreter ••••••• 59 APPENDIX: SYSTEM CONVENTIONS 77 Initiator/Terminator • • • • 59 Output Writers 60 Names •• 77 Master Scheduler • • • • • 61 Subprogram Linkage 78 SECTION 6: TASK MANAGEMENT 63 Program sharing • • 78 Single-Task Operations 63 Actual Flow of Control 64 Intertask communication • 78 Multitask Operation ••• 64 Use of WAIT • • • • 78 Task Creation -- ATTACH 65 Resource Allocation 66 Operator messages • '78 Tasks As Users of Resources • 67 passing Resources to Subtasks 68 Control Section size 78 Event Synchronization ••••• 68 WAIT and POST Macro-Instructions 68 Character set considerations 78 Enqueue (ENQ) and Dequeue (DEQ) Source Language Debugging and Macro-Instructions 70 Maintenance 79 Task Priorities 71 Task Termination • • • 72 Volume Labels 79 Main Storage Allocation • 74 Track Address Independence 79 Main Storage Allocation in a Multitask Environment 75 GLOSSARY 80 Storage Protection And Protection Boundaries •••••••••••• 75 INDEX •• 87 11 S $ ILLUSTRATIONS FIGURES Figure 1. Operating System/360 . • • 8 Figure 30. Delays Expected in Sub- Figure 2. Subprograms Existing at program • •• .•••. 47 Different Levels of Control Figure 31. No Delays Expected. 47 13 Figure 32. A Reenterable Program that Figure 3. Subprograms Existing at the Requests Its Own Temporary Same and Different Levels Storage •• .... 49 of Control • • • • • • 14 Figure 33. Chain of Symbolic Figure 4. Program Preparation. • 14 References ...•.. 54 Figure 5. The Input Job Stream • • • 15 Figure 34. Typical Input/Output Figure 6. Sequential Scheduling Devices • • • • • • • • • 56 System • • • • • • • • 16 Figure 35. Multijob Initiation • 60 Figure 7. Priority Scheduling System 17 Figure 36. Actual Flow of Control. • 64 Figure 8. Task Representation. • • • 18 Figure 37. Job Step-Task Relation- Figure 9. Switching Control Among ship. 65 Tasks ••••••••••• 19 Figure 38. Situation Immediately After Figure 10. Volume Initialization and Initial Program Loading • 66 the Volume Table of Contents Figure 39. Situation With Reader, 23 Writer, Initiator, and ~"igure 11. Catalog Search Procedure • 24 One Job Step. • • • • • • 66 Figure 12. The Queued Figure 40. Situation After Initiating Telecommunications Access Three Concurrent Jobs • • 66 Method • • • • • • • • • • 28 Figure 41. Resource Queues • • • • • 68 Figure 13. Components of a Message •• 29 Figure 42. Intertask Synchronization 69 Figure 14. Dynamic Buffering ••••• 31 Figure 43. Situation After READ ••• 69 Figure 15. Simple Buffering - Move Figure 44. Situation After Execution Mode • • • • • • • • • • • 32 of WAIT • • • . • • • • • 70 Figure 16. Simple Buffering - Locate Figure 45. Situation at Completion Mode • • • • • • • • 32 of Input/Output Operation Figure 17. Exchange Buffering - 70 Substitute Mode •••••• 33 Figure 46. Abnormal Termination of a Figure 18. Data Control Block Being Task. • • • . • • • • • • 73 Filled in. • • • • . • • 34 Figure 47. Abnormal Termination of a Figure 19. Actual Program Flow That Subtask • • • • • • • • • 73 Starts on Input/Output • . 35 Figure 48. Deferred Exit at Abnormal Figure 20. Execution of a Load Module End of Task • • • • • • • 74 Within a Task •••.• ~ • 40 Figure 21. Subprogram Within a Program 40 Figure 22. Deferred Exit to Subroutine 42 Figure 23. Overlay Tree Structure 42 Figure 24. The LINK Operation . 44 Figure 25. Nested Subprograms • • 45 Figure 26. Use of XCTL Macro­ TABLES Instructions • . • • 45 Figure 2 7. Uses of LOAD Macro­ Table 1. Access Method Summary 37 Instructions • • .. 46 Table 2. Names of Installation