MVS

1. MVS (Day 1)

2. Objectives • To introduce mainframes • Hardware and Software • To introduce internals of MVS • To introduce VSAM and non-VSAM data sets • To introduce job management in MVS • To introduce various subsystems and facilities • To introduce TSO and ISPF

3. Prerequisites • Knowledge about basic computer architecture • Basic knowledge in Operating System concepts • Knowledge about I/O and communications

4. Evaluation Strategy

5. References 1. Robert. H. Johnson, MVS – Concepts and Facilities, McGraw-Hill Book Company, 1989. • Doug Lowe, MVS JCL - Mike Murach & Associates, 1994. • MVS/DFP - IBM Manual 4. Doug Lowe , MVS TSO PART1 CONCEPTS AND ISPF, Mike Murach & Associates, 1991. 5. Jay Ranade, Hirday Ranade, VSAM Concepts, Programming, and Design - McGraw-Hill 6. IBM On-line Manuals - IGG3L100, IGG3U100 and IGG3V400. On MVS.

6. Course Plan Day 1 • Introduction to Mainframes • Hardware & Software Evolution • Distinguishing characteristics of a mainframe OS • Basic Mainframe Architecture • Address spaces • Mechanisms in Multiple Virtual Storage Day 2 • Data set management • Describe the organization of data sets • VSAM and Non-VSAM • Job Management • How does JCL specify its processing requirements ? • Job Entry Subsystem • Phases of a job Day 3 • Various subsystems & facilities most commonly found on a typical Mainframe system • System generation & initialization • TSO/ISPF

7. Agenda – Day1 • Introduction • Comparison of computer types • Personal, Mini & Mainframes • Evolution of Mainframe hardware and software • Distinguishing characteristics of a mainframe OS • Basic Mainframe architecture • I/O device structure • Concepts & terminology • Idea of address spaces • Mechanisms in Multiple Virtual Storage • MVS address space organizations ( Memory maps )

8. Basic Components of Computer Systems

9. Classification of computers Personal Computer Mainframe Computer Super Computer Mini Computer

10. Personal Computers

11. Minicomputer

12. Mainframe

13. Super Computers . High Processing capacity Uses: . Scientific computations . Military applications

14. Mainframe Hardware Evolution

15. Mainframe System Software Evolution … • DOS/VSE • OS/360 • PCP • OS/MFT

16. Mainframe System Software Evolution • OS/MVT • OS/VS1 and SVS • MVS • Z/OS

17. Mainframe OS - characteristics • Virtual storage • Multiprogramming • Spooling • Batch processing • Time sharing

18. Virtual storage • Technique that lets a processor simulate a large amount of main storage from a smaller installed real storage. • Uses disk storage as an extension of real storage. • At any given moment only one program and its data need be in real storage.

19. Multiprogramming • More than one program executing at the same time. • Key : I/O waits take a long time compared to CPU operations. • Only a simulation again.

20. Spooling • Intercepts and redirects printer output to a disk file. • Each programs’ output stored separately. • Facilitates effective sharing of I/O devices and better system throughput.

21. Batch processing • Batch processing is - • Non interactive • Off line • JCL describes a batch job - programs, data and resources required. • Job scheduler : submits jobs for execution based on scheduling algorithm.

22. Time sharing • Time sharing makes on-line, interactive processing possible. • Each user has access to the system and a gets a time slice repeatedly. • TSO used to login, create, maintain and store JCLs. • Processing is generally as a batch job in background.

23. channel 0 channel 1 channel 2 channel 3 Main storage channel 4 CPU channel 5 channel 6 channel 7 Basic Mainframe architecture … Processor A family of processors from IBM

24. Basic Mainframe architecture ... • Processor-CPUs+Main store+channels • cache • expanded storage • Multiprocessing (more than one CPU) • PR/SM - Processor resource / systems manager

25. Basic Mainframe architecture ... • Channels - • provides a path between a processor and an I/O device. ( 4.5 MB/sec, 400-foot ) • Each channel can connect to upto 8 control units each of which is connected to an I/O device. • A channel is intelligent ( a CPU in itself ) • ESCON - Enterprise System Connection - based on fiber optics ( 17 MB/sec,26 miles )

26. I/O Devices • Unit record devices • card devices & printers • Magnetic tape devices • sequential access only • Direct access devices • disk drive, DASD, auxiliary, .secondary storage • random access possible

27. Magnetic Tapes • It is one of the commonly used I/O. • Coated with a magnetic material on both sides of the tape. • Data is stored by Magnetizing the ferrite coating. • Sequential access of records. • Used for bulk storage and easy transportation.

28. Platters Direct Access Storage Device (DASD) • A DASD consists of many disk packs or volumes: • Data on both sides

29. TRACK 807 TRACK 000 DASD - Tracks & Cylinders

30. READ-WRITE HEADS DASD - Actuator

31. DASD: Data format … • There are two types of Data Formats: • Fixed block data format • Count Key data format (CKD format)

32. DASD - Data format • CKD ( count-key-data) devices - • Store data in variable-length blocks • Each data block preceded by a count area and a key area ( which should be met before data in dir of rotation ) • Gaps to separate count, key and data areas.

33. DASD - control units … • Each type of DASD requires two types of control units to connect to a channel : • String controller : • attaches a group of DASDs of same type ( a string ) • Storage control : • connects upto 8 DASD strings to a channel • Cache between processor & drive. • Support for more than one channel connection to processor.

34. DASD - Control units

35. Data communications equipment … • Lets local & remote terminals access a system : • host system • communications controller • modems • telecommunication lines • terminal systems

36. Data communications equipment

37. Terminals • 3270 terminals are the standard. • It is a subsystem of many terminals, printers and controllers • Terminals can be emulated on PCs which accesses the mainframe over wide area links.

38. Concepts & terminologies

39. Address space • What is an Address Space? • An address space is a complete range of addresses that can be accessed by a processor.

40. 64 bit Addressing (z/OS) 2 GB “Bar” 16 MB “ Line” 31-bit Addressing (MVS/XA) Addressability of different Systems • Depends on number of bits used for addressing : • System 370 : 24 bit addressing, 16 MB max • 370 XA, ESA 370,390 : 31 bit addressing, 2GB max. • Z series – 64 bit addressing 16 EB 24 bit Addressing (MVS)

41. Multiple Virtual Storage … • MVS simulates several address spaces, each independent of the other and representing an user, job or a OS subsystem. • Mechanisms used to support MVS : • Paging • Swapping

42. Multiple Virtual Storage ...

43. Paging … • Pages are 4K sections on virtual store ( DASD ). • Page frames are 4K sections in real store ( main memory ). • Page table maps pages to page frames. • Page fault when program refers to data in a storage location not in real store.

44. Paging • Page-in when MVS loads a new page into a page frame • Page-out when data in a page-frame is written back to DASD. • OS code responsible for paging cannot be paged out.

45. Expanded Storage: • Acts as large buffer between real storage and page data sets ( virtual store ). • Improves efficiency of virtual storage operations.

46. Swapping … • Transfer of entire address spaces in and out of virtual store. • Swapping is like paging, only at a higher level and across address spaces.

47. Swapping

48. Program modes • Real mode • not pageable or swappable • OS part responsible for implementing virtual memory, always resident • Virtual mode • Other processes that can be paged or swapped

49. MVS/370-Memory map … • System area • OS programs & data, common to all address spaces, nucleus, real mode • Private area • User region + unallocated • Common area • OS programs & data, common to all address spaces • SQA, PLPA and CSA

50. MVS/370 - Memory map ...