Mainframe Basics

Mainframe Basics & MVS

Course Mechanics • Course Type: Self Paced or Facilitated • Course Notes: –If training is Facilitated, Notes are located in the Notes View. (Please see View Master/Notes Master to see the Notes View.) –If training is Self Paced, Notes are located in Slide View.

• This course is best viewed in Slide Show Mode. You can download this course to your desktop (if desired) for printing and note taking.

• Length of Course: 32 hours • Course Audience: All who are new to Mainframe Technology 11 Nov, 2003

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Prerequisite Training • None

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Supplementary Training • Training on JCL, VSAM, COBOL, CICS & DB2 will help to become a developer in the mainframe technology.

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Agenda Classification of Computers Mainframe Overview MVS Characteristics Of Mainframe MVS – Management of User Jobs MVS Concepts ISPF – An Introduction IBM Utilities – An introduction Advanced Mainframe Concepts / Products Summary NOTE - Click on arrow to advance directly to the associated agenda topic. 11 Nov, 2003

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Course Objectives • Objective A – To give an introduction to the concepts of mainframes and the MVS Operating System.

NOTE - Click on back arrow to return to the Agenda. 11 Nov, 2003

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Classification of computers: Classification of computers: Computer systems used for business purposes are divided into three classes. 1. Micro Computers 2. Mini Computers 3. Mainframe Computers Although these divisions are loosely based on the size of the computer systems, there are no hard and fast rules for deciding exactly where one category ends and the next begins .In other words the categories overlap. 11 Nov, 2003

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Classification of computers: Several factors determine the size of computer system. 1. Hardware configuration 2. The nature of its application 3. The complexity of software. Basically all computers consists of two types of components, Processor and I/O devices. 11 Nov, 2003

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Mainframe Overview

OS family: In the late 1960’s there were two versions of OS in wide spread use. They are : 1.OS/MFT 2.OS/MVT Actually they differed in the way they handled multi programming. 11 Nov, 2003

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Mainframe Overview MFT Stands for multi programming with fixed number of tasks. It preallocated a fixed number of partitions where user jobs could execute. So under MFT, the number of jobs that could be multiprogrammed is equal to number of preallocated partitions. MVT – stands Multiprogramming with variable number of tasks, the logic is just opposite to MFT. The number of jobs that could be multiprogrammed depends on storage available and size of partition is decided during run time and it is variable. 11 Nov, 2003

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MVS MVS: (Operating System) MVS offers multiple virtual storage that means each multiprogrammed job is given its own virtual storage address space which can be up to 16MB or 2GB based on our MVS version. MVS Versions:  MVS/370 –Older version of MVS that limits a user’s address space to 16MB.  MVS/XA – New version that allows up to 2GB address space for each user.  MVS-ESA –latest version of MVS which let each job access more than one 2GB address space. 11 Nov, 2003

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MVS O/S 390 : IBM’s OS/390 was the next generation of Operating Systems. Z / OS : Currently , this is the latest operating System by IBM. When newer versions are released, the mainframe operations group plans for the upgrade and converts all the current products to the upgraded version.

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Characteristics of Mainframe Virtual Storage:  Virtual Storage ,which is simulated to exist by MVS.  Storage is not physically exist in main memory.Its actually expansion of Real storage which is in disk only.But always active pages will be in Main storage and so the processing will be faster.  Because of virtual storage ,the number of programs that can be multiprogrammed increased. So the productivity goes up overall though the operating system needs to perform additional virtual storage control functions. 11 Nov, 2003

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Characteristics of Mainframe Multi-Programming:  More than one program run concurrently in the system.(Note: anyway only one program will run at a time)  Improves overall productivity of system installed.  The central component of operating system, supervisor program which gives the processor control to one job. When the job goes for some i/o operation it gives the control back to supervisor. Supervisor decides based on priorities assigned to the jobs in queue and gives the control to highest priority. 11 Nov, 2003

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Characteristics of Mainframe Spooling: Outputs are written to disk devices and from there it will be written into Printer when it is available. (otherwise due to Multiprogramming concept of MVS, various programs reports will be mixed up) Batch Processing: JES2/3 will take care of Priority. Time-Sharing (Foreground Processing): TSO- Here, user directly interacts with system. examples - all the ISPF operations. 11 Nov, 2003

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Configuration of Mainframe HARDWARE CONFIGURATION Mainframe computer system is a large collection of computer hardware devices. Consists Mainly of two categories: Processors I/O devices

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Processors PROCESSORS: The Central components of the Mainframe Computer Systems are the Processors. MVS runs on processors that have evolved in the past years to enterprise systems. The MVS runs on processor system/370, which was developed 30 yrs back but IBM still uses them because they have enhanced the OS capabilities significantly and in the future also they will make it compatible to move on with the advancements. Basic Components are  CPU  MAIN STORAGE  CHANNELS.

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Processors MULTIPROCESSING: More than one processor was introduced to increase the processing rate and the system availability also increases. Here processors share access to main memory and the OS determines how each processor is utilized. Situations where four processors are used, operates in two modes: As a single four processor & As two independent 2-CPU processors. In the latter case the main storage and the channels are split between the two processors. Depending on the operational needs the installation may vary, Initially the multiprocessor installation reported to VM, an operating system designed to emulate the multi computer systems and configured to take advantage of the multi computer systems. 11 Nov, 2003

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Processors PR/SM: To address this problem PROCESSOR RESOURCE/SYSTEM MANAGER was introduced. Here the multi CPU processor was split into several partitions. Each of this partition can operate as an independent system. The advantage of this system was one of these partition could serve as the back up of the PRIMARY PARTITION. If the primary partition fails at any point of time the back up starts to operate from where the primary stopped. During these situations of failures the PR/SM also reconfigures the I/O channels assigned to the various partitions without disrupting the processing. 11 Nov, 2003

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IO Devices CHANNELS: This is the path between the processor and the I/O devices. There are 8 channels numbered 0 thru 7, which can communicate and pass data between the processor and the devices. Each channel can connect up to eight devices called as CONTROL UNITS. Depending upon the Processor and device, a control unit can be fixed within the processor’s cabinet or device cabinet or in it’s own cabinet. A channel itself is a small computer in the sense that it executes I/O instructions called Channel Commands that operate the I/O devices that are attached to it. As a result the channel frees the processor to execute other instructions. Since channel processing overlaps CPU processing, overall system performance improves. 11 Nov, 2003

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IO Devices The main purpose of these devices are to provide with input, receive output and provide secondary storage. The common types of I/O devices are Unit record devices Magnetic tape devices Direct access devices & Telecommunication devices

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IO Devices Unit record devices: These are two types of Unit record devices. They are card devices and printers. Each record processed by the device is a physical unit hence the name “Unit record devices”. Incase of card devices, each record is a punched card. Similarly for a printer it is a printed line. Card devices are not commonly used anymore are of three types. They are:  Reader  Puncher  Reader/Punches.

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IO Devices Impact Printers: Produce printed output by striking an image of characters to be printed against ribbon, which in turn transfers ink to the paper. The most common type of impact printers uses a train of characters that spins at a high speed; when the correct character passes a print position, a hammer a strikes the character against the ribbon to produce the printed text. Most impact printers operate in the range of 600 to 2000 lines per minute.

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IO Devices Non-Impact Printers: These printers use Laser Technology to print text and graphic images. The IBM 3800 printing Subsystem can print at rates of up to a remarkable 20000 lines per minute. The actual speed of this system depends on the size of each page and the number of lines per inch, since the mechanism involved can transfer images to the paper an entire image at a time.

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IO Devices

For a standard size paper (11x14) and normal print size (6 lines per inch), the 3800 can print 10200 lines per minute. At this transfer rate the 3800 can process more than a mile and a half of paper each hour.

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IO Devices

Magnetic Tape Devices: A tape drive reads and writes data on a magnetic tape that’s a continuous strip of plastic coated on one side with metal oxide. Tape drives process tapes that’s sealed within a special type cartridge but earlier most tape drives processed tape wrapped around an open reel much like an old fashioned reel to reel tape recorder. The amount of data a reel or cartridge of tape can contain depends on the length of the tape and the density used to record the data. Density is a measurement of how many bytes are recorded in one inch of tape. Tape densities for standard reel tapes are usually 1600 or 6250 bytes per inch. Cartridge tape drives can record data using much higher densities. 11 Nov, 2003

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IO Devices - Magnetic Tape Devices (Cont.)

Data records are normally written to tape in-groups called blocks, and the empty areas are called as gaps. These separate the blocks from one and other. The larger the block, better the usage of tapes and their efficiency. But one drawback is that, A buffer is required is required to store these blocks in the main storage. The other major drawback is that the records have to be stored sequentially. To read the 50000th record on a tape the 49000 records have to be read to reach that particular record. So direct access cannot be performed here.

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IO Devices - Magnetic Tape Devices (Cont.)

The tape drives are used for offline storage of large quantities of data. To attach a tape drive to a processor a control unit is required. For some models the control unit is inside one of the tape drives and for the other models it is in a separate cabinet.

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IO Devices Direct Access Drives: The official IBM term for a disk drive is direct access storage device or DASD. These allow direct and rapid access to large amount of data. They have become a key component of mainframe systems. They are not only used to store user programs and data but also to store programs and data for operating systems functions. Disk drives read and write data on a disk pack (also called as volume). A disk pack is a stack of metal platters coated with metal oxide material. Data is stored on both the sides of the platters. Earlier removable disk pack’s were used but now permanent disk pack’s are used. The advantages of fixed disk packs are that they are more reliable and faster. 11 Nov, 2003

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IO Devices

Tracks & Cylinders: Data is recorded on the usable surfaces of a disk pack in concentric circles called tracks. The number of tracks per surface varies with each device type. For example a disk pack consisting of 19 usable surfaces, each with 808 tracks has a total of 15352 tracks. Access mechanism or Actuator is the component that reads or4 writes data on the tracks of a disk pack. The actuator has one read/write head for each recording surface. When the actuator moves all of it’s head move together so they are all positioned at the same track of each recording surface. As a result the disk drive can access data on all those tracks without moving the actuator. 11 Nov, 2003

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IO Devices -

Tracks & Cylinders (Contd.)

The tracks that are positioned under the heads of the actuator at the one time make up a cylinder, As a result, there are as many tracks in a cylinder as there are usable surfaces on the pack.

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IO Devices

Device capacity and data format: There are two basic types of disk drives that store their data in different formats. They are count key data devices where data is stored in variable length blocks and the other format is called as fixed block architecture, stores data in fixed length blocks which is not supported by MVS. So we will deal only about CKD devices, here a count area and a key area precede each block. The disk revolves counter clockwise, the read/write head encounters the count and key areas before the data area. The count area contains the information needed to locate and process key and data areas.

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IO Devices - Device capacity and data

format (Contd.) One of the problems with CKD devices is that the data capacity of each track depends on the size of the blocks used to store the data. That’s because gaps required to separate the count, key and data areas. Just as gaps are required on magnetic tapes. The data efficiency depends on how the blocks and gaps are used. When more blocks are stored, more gaps are also used so the total capacity reduces. 11 Nov, 2003

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IO Devices Control Units: Each type of DASD device requires two kinds of control units to attach it to a processor channel. The first called string controller, attaches a group of DASD’s of the same type, the resulting group called string. The number of devices that can be connected on one string depends on the device type. For the3 3390 model around 32 drives can be connected to a string. The second type of control unit called as string controller connects up to eight strings of DASD units to a channel. The most common type of storage control is the 3990, which attaches two strings. If both the strings are 3990 drives up to 64 drives can be connected.

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IO Devices - Control Units (Contd.) The 3990 storage control provides high-speed cache storage that acts as a buffer between the processor and disk units. Special circuit keeps track of what data is accessed most frequently and tries to keep that data in the cache storage. When data is accessed again, it directly loads the data from cache than accessing the DASD. Depending on the model the size of the cache can range from 32mb to 1024mb & improves the system’s overall performance. In addition the 3990 storage control also provides the facility of connecting to more than one channel to the processor. This enables several simultaneous disk operations to be processed at one instance. The smallest 3990 models support up to four standard channel connections and the largest can support up to 16 standard connections or 128 ESCON channel connections.

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IO Devices Data communications equipment: Lets an installation create a data communications network that lets the users at local terminal and remote terminal to access the system. Elements of a data communications network are:  The Host  Communications Controller  Modems  Telecommunications Lines &  Terminal Systems

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IO Devices The center of the network is the host system and the processor. The control unit that attaches to the host system’s channels is called the communication controller. This manages the communication functions necessary to connect remote terminal systems via Modems and Telecommunication Lines. If the terminal system is located close enough to the host system, the Modems and Telecommunication Lines can be eliminated. Then, the terminal can be connected directly to the communications controller or one of the host processor’s channel. 11 Nov, 2003

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MVS Management of user jobs: JOB: Job is an execution of one or more related programs or procedures in sequence. Each program or procedure is called a job step. E.g. To get a report of an organization’s employees in alphabetic order, first program should sort the file by name and the second program prints the report. Here, one job has 2 steps.

JOB Life cycle: 1.The job is submitted 2.The job is selected for execution. 3.The job is executed 4.The job’s output is processed. 5.The job is purged.

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MVS Management of user jobs: Job Entry Subsystem: This MVS component keeps track of jobs that enter the subsystem, presents them to MVS for processing and sends their spooled output to correct destination.(printer) Original version of OS did not provide this facility. It has job scheduler ,a relatively crude form of present JES was totally inadequate most installation’s need. 11 Nov, 2003

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MVS Management of user jobs: Houston Automatic spooling program was used which ran as a job in scheduler with most of the functions of job scheduler and provided most efficient operation and comprehensive control than the job scheduler alone.(HASP) Asymmetric multiprocessing system (ASP) was used in shops which had more than 1 processor. It gave good control of job processing in multiprocessing environment. When MVS was announced, IBM integrated the functions provided by HASP and ASP into operating system by providing the JES. But since both were incompatible with each other, two subsystems were created .JES2 for HASP and JES3 for ASP. 11 Nov, 2003

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MVS Management of user jobs: How JES2/JES3 process jobs: Job entering into subsystem: By SUBMIT command in the jcl .JES2 (internal reader) read the job stream from the DASD file and copy it to job queue, which is a part of special DASD file called JES spool.

Job selected for execution : Based on class and priority jobs are selected for execution. Job classes are assigned based on the processing characteristics of the job. job will execute within 15 or 30 minutes etc. of submission. These definitions will be done at installation time. 11 Nov, 2003

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MVS Management of user jobs: Initiator is program that runs in the system region of address space that’s eligible for batch job processing. Each initiator can handle one job at a time. 1–

A

2–

B,C

3–

C,D,E

The number of active initiators on a system and as a result number of address spaces eligible for batch job processing determines the number of batch jobs that can be multi programmed at once. Initiators can be started when MVS is activated and that can be stopped or started by an operator while MVS is running.

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MVS Management of user jobs: Job Execution: The first thing an initiator does after selecting a job for execution is to invoke a program called interpreter. The interpreter’s job is to examine the job information passed to it by JES and create a series of control blocks in the scheduler work area(SWA), a part of address space ‘s private area. These control blocks describe all of the datasets the job needs. After the job creates the SWA blocks the initiator goes through three phases for each step in the job.

Allocation routines: Allocate all the required datasets needed. 11 Nov, 2003

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MVS Management of user jobs: User region: The initiator builds a user region where user programs can execute, loads the program into that region and transfers control to it. As the program executes it uses the control blocks for the resources allocated to it. Un allocation routine: When program is completed, the initiator invoke this which release any resource used by job step. Based on output class, the processed outputs are sent and the job is purged from the system. Simply put, that means JES spool space used by the job freed so it can be used by other jobs. Any JES control blocks associated with that job are deleted. 11 Nov, 2003

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Data Management By MVS: Dataset: Collection of related data that is managed as MVS as a unit. Within the dataset, data is organized into smaller units called records, which can be processed individually by application programs. Label Processing: When dataset is normally stored on disk or tape MVS normally identifies it with special records called labels. To access a dataset correctly, the label information passed in the JCL and what is there in MVS should match. 11 Nov, 2003

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Data Management By MVS: DASD labels: Volume label : Unique six char volume number – cylinder 0 track 0 record 3 contains volume number and pointer to VTOC. VTOC : contains five format of records. FORMAT-4 information abt VTOC itself. FORMAT-1 pointers to dataset which has maximum of 3 extents(1 primary,2 extents) information. FORMAT-3 pointers to dataset which has the remaining 13 extents FORMAT-2 ISAM files FORMAT-5 free extent pointers(26 extent-1) 11 Nov, 2003

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Data Management By MVS: Tape Label: Unlike DASD, for tape labels are optional. Here labels are stored along with files rather than separately. tape file started with HDR1 which is followed by files data and at the end EOF1 end-offile label exist.

Catalogs: Many MVS installations have hundreds of DASD volumes and thousands of datasets. So it is impossible to remember the DASD for accessing dataset and we cannot give Volser for each dataset we want. So cataloging is necessary. 11 Nov, 2003

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Data Management By MVS: There are two types of catalogs: One master catalog and unlimited number of user catalogs.

Master catalog: 1.System dataset entries 2.User catalog entries

Importance of high level qualifier: The high-level qualifier and the user catalog name are the same. More often the high level qualifier will be alias of the actual name.(alias is simply alternate name for something, in this case user catalog) Fst-qualifiercataloguser catalogdasdvtoc dataset

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Data Management By MVS: Dataset organization: Within a dataset, data can be organized in one of several ways depending on how the data will ultimately be processed.

NON-VSAM: 1. Sequential 2. Indexed sequential 3. Direct 4. Partitioned 11 Nov, 2003

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Data Management By MVS: Depends on dataset purpose, file organization is selected. For example, in every day transaction only very few records will be updated and they are random means then Indexed sequential or Direct is the best. For payroll file Sequential is well enough.

Dataset processing: Allocation at 3 levels: 1.Unit is selected and allocated (SYSDA,TAPE) 2.Volume is allocated (VOL=SER= ) 3.Dataset on that volume allocated. (VTOC updated in case of disk) 11 Nov, 2003

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Data Management By MVS: There are 3 access methods available:  Basic ( BSAM,BISAM,BDAM)  Queued (QSAM,QISAM)  VSAM (KSDS,ESDS,RRDS)

When the file is opened in program: The relation between program, dataset and access method has to be established. This connection is established through a special control block called DCB. Similarly for VSAM it is ACB. 11 Nov, 2003

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Data Management By MVS: DCB,ACB are basically tables where the vital information about status of dataset is stored as it is processed. OPEN : Initialize this control block and information about dataset comes from JCL/Program/catalog/label. I/O requests: Access methods used for accessing required records. CLOSE

: File is disconnected from the program.

DEALLOC

: Files are automatically deallocated when the job is finished with it.

During deallocation disposition is the key thing which decide what to do with that file. 11 Nov, 2003

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Data Management By MVS: Storage Management Subsystem:  New Feature of MVS  Removed many of the manual procedures that are associated with managing datasets, such as which volume the dataset should be stored on, amount of space to allocate the dataset, when the dataset no longer need and can therefore be deleted or moved to offline storage.  Based on job name ACS routine assign the corresponding data class, storage class, management class for the dataset.

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MVS Concepts VIRTUAL STORAGE: This is a facility that simulates a large amount of main storage by treating DASD storage as an extension of real storage . In other words when virtual storage is used, the processor appears to have more storage than it actually does. ADDRESS SPACE: To refer to a particular location, we need to use an address that indicates the storage location’s offset from the beginning of memory. The first byte of storage is at address 0, the second byte at 2. etc . Address space is simply the complete range of addresses and as a result the number of address locations that can be accessed by the computer. The maximum size of address space is limited by the number of digits that can be used to represent address. 11 Nov, 2003

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MVS Concepts MULTIPLE VIRTUAL STORAGE:  MVS not only simulates more storage but also uses real storage to simulate several address spaces, each of which is independent of the others . In fact MVS derives its name from this technique (Multiple virtual storage) PAGING:  We know real storage is very low and that raised the need for virtual storage. Implementation of virtual storage is possible through Paging concept. Lets see how it works. 11 Nov, 2003

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MVS Concepts  Virtual storage divided into 4K pages. Real storage divided into 4K page frames. DASD area used for virtual storage called page dataset is divided into 4K page slots each of which holds one page of virtual storage.  Page fault , Page-in, Page-out: When a program refers to a page that is not in real storage page fault occurs. When that happens MVS locates the page that contains the needed data on DASD and transfers it into real storage. The least used page is released from real storage to page dataset (page-out) and new page put into real storage.

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MVS Concepts

Usually page frames in real storage contain pages from more than one address space. MVS keep track of what pages are in what page frames by maintaining tables that reflect the current status of real storage and of each address space. As long as the corresponding address space is active, the corresponding tables cannot be paged out. They should be in real storage.

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MVS Concepts

EXPANDED STORAGE: This storage acts as a large buffer between real storage and Page dataset. During page out, the pages are moved out to expanded storage. This transfer occurs at CPU speed and not DASD speed and so the operation is almost instantaneous. Pages are written into actual page datasets when the expanded storage becomes full.

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MVS Concepts

SWAPPING: This is same as paging but at a higher level. Rather than move small 4K pieces of virtual storage in and out of real storage , swapping effectively moves entire address space in and out of virtual storage. Because paging occurs only for address spaces that are currently in virtual storage , paging does not occur for address spaces that are swapped out.

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MVS Concepts During swap out, the address spaces’ critical pages – the ones that contain the tables that keep track of the location of each virtual storage page for address space are written to a special dataset called swap dataset. Later when the system can accommodate the job again , the address space is swapped in so it can be processed again. PROGRAM MODES: Real mode: Programs that cannot be paged or swapped. The programs which are responsible for virtual storage functions and tracking should be in main storage always. 11 Nov, 2003

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MVS Concepts  Critical time dependant channel devices communication programs also non –page able. Most of the programs actually running in virtual mode only. DATA WITHIN EACH ADDRESS SPACE : SYSTEM AREA – NUCLEUS/ COMMON AREA:  Operating system programs and data are in system area and common area. This is common and shared by all. That is system area and common are the same for each address space.  This controls the operation of paging and swapping of virtual storage. System area operates in real mode. 11 Nov, 2003

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MVS Concepts  Three important operating system components are in common area. SQA: SYSTEM QUEUE AREA : Important system tables and data that are used by programs residing in the nucleus (Non-Pageable) CSA: COMMON SERVICE AREA : Similar to SQA but pageable PLPA: Pageable Link Pack Area: contains some operating system programs that don’t have to be fixed 11 Nov, 2003

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MVS Concepts This is the portion of address space that contains data that are unique for each address space. Within each jobs private area, System region: Area of storage used by operating system programs that provide services for user programs running in the private area. At the top of private area, three local system areas that contain information that applies only to the private area of particular address space. LSQA: Local System Queue Area: Tables used to control the private area , including the tables needed to manage the private area’s virtual storage. During swap out, this is what written into swap dataset.

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MVS Concepts Scheduler work area: SWA tables used to manage the execution of jobs and programs within the private area. Sub Pool : additional system information. 3.User Region: This is the place where the program actually execute. The size of user region varies depending on the amount of storage required by the program being executed . (Max 10 MB to 12 MB) Remaining space is unallocated storage. 11 Nov, 2003

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MVS Concepts MVS Concepts MVS/ESA DATA SPACES AND HYPERSPACES  Here one user can have access to more than one address space. Depending on the requirements of application, the additional address spaces created for data storage can be one of the two types :data spaces or hyperspaces  Data spaces resides in normal storage and are subject to paging and swapping and they are managed by user-written programs.  Hyperspaces are in expanded storage and managed by MVS/ESA. 11 Nov, 2003

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MVS Classification Concepts of computers: MVS Concepts SYSTEM GENERATION AND INITIALIZATION:  System generation and initialization are activities that are required to establish a working MVS system.  System generation is the process creating an MVS system, and system initialization is the process of starting a previously generated MVS system.  Both of the above are the responsibility system programmers staff.

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MVS Classification Concepts of computers: MVS Concepts SYSTEM GENERATION: For the installation of the MVS system, IBM sends the basic components that make up MVS on a series of tapes called distribution libraries. System generation is only a part of the overall process of installing MVS from the distribution libraries, selects and assembles the various components an installation needs to create a working MVS system. To control System generation, often called sysgen, a systems programmer codes special macroinstructions that specify how the MVS components from the distribution libraries should be put together. 11 Nov, 2003

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MVS Classification Concepts of computers: MVS Concepts Interestingly, an installation must already have an MVS system is required before it can generate a new one. That’s because an existing MVS system is required to execute the sysgen macro instruction. Fortunately, most installations perform sysgen to upgrade to a newer version of MVS or to make changes to their current version. So they can use their current version of MVS to execute the sysgen. For new installations that don’t already have an MVS system, the system installation process includes setting up a small, limited function MVS system that can execute sysgen for the complete, full function MVS system. 11 Nov, 2003

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MVS Concepts SYSTEM INITIALIZATION:  Once a MVS system has been generated, it can be used to control the operation of the computer system.  To begin a system initialization, the system operator uses the system console to start an initial program load or IPL. That causes the computer system to clear its real storage and begin the process of loading MVS into storage from the system libraries and ready to process your work.

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MVS Concepts

Initialization options come from one of two sources:  The system operator or a special system library called SYS1.PARMLIB.  By specifying options in SYS1.PARMLIB, MVS can initialize with little operator intervention.

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MVS Concepts Here are few examples of the system data sets:  SYS1.NUCLEUS  SYS1.PARMLIB  SYS1.LINKLIB & SYS1.LPALIB  SYS1.MACLIB  SYS1.PROCLIB  SYS1.CMDLIB

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MVS Concepts SUBSYSTEM AND OTHER FACILITIES:  A complete production MVS system contains a variety of other software products. Subsystems are those software products, which operate in their own address spaces under the control of MVS system. What ever they do in that address space is of no concern for the MVS. These subsystems provide services that duplicate services provided by the operating system.  Multiprogramming, job management and spooling are few examples of the services that are provided by the subsystem, which are duplicated. 11 Nov, 2003

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MVS Concepts Some of the examples are:  JES2/JES3  TSO & ISPF  TELECOMMUNICATIONS  CICS  IMS  DB2

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ISPF INTRODUCTION

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ISPF - Introduction

What is ISPF? The Interactive System Productivity Facility is a Dialog Manager that provides tools to improve program, dialog and development productivity and control.

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ISPF - Introduction

What the ISPF Editor does? ‘Edit’ Option (usually 2) . It is used for create, display and change data stored in ISPF libraries or other PDS or PS.

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Line Commands

        

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Insert or Delete lines Repeat lines Rearrange lines or Overlay portions of lines Simplify text entry and formatting Define an input mark Shift data Include or exclude lines from the display Control tabs and boundaries for editing Convert some types of special temporary lines to data lines Introduction to Mainframe

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Primary Commands           11 Nov, 2003

Control your editing environment. Find a specific line. Find and change a character string. Combine several members into one. Split a member into 2 or more members. Submit data to the job stream. Save the edited data or cancel without saving. Sort data. Delete lines. Run an edit macro. Introduction to Mainframe

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Edit macros • Edit Macros are ISPF Dialogs that run in the PDF editor Environment. • Edit Macros are nothing but the line or primary commands or combination of line and Primary commands.

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Line Commands

       11 Nov, 2003

I R M D C TE TS

Insert Repeat Move Delete Copy Text Edit Text Split Introduction to Mainframe

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Line Commands

       11 Nov, 2003

UC LC CC DD MM (( ))

-

Upper Case Lower Case Block Copy Block Delete Block Move Shift Left Shift Right

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IBM Utilities INTRODUCTION

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Introduction to IBM Utilities

    

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What is an utility? What are the types of utilities? What can you do with utilities? How to use them? Some examples of utility programs

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ANY TYPICAL UTILITY JCL //JOBNAME JOB (ACCOUNTING INFORMATION), // PROGRMAMER NAME, //STEPNAME EXEC PGM=UTILITY-NAME, // PARM=PARM-VALUE //PRINTNAME DD SYSOUT=PRINT-DEVICE-CLASS, //INPUT-FILE DD INPUT-FILE-FEATURES //OUTPUT-FILE DD OUTPUT-FILE-FEATURES //WORKFILE DD WORK-FILE-FEATURES //INPUT-DATA DD * *********** /* 11 Nov, 2003 Introduction to Mainframe

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IEBCOPY  How to use them?    

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Copy a PDS Compress a PDS Merge PDSs Selecting or excluding specified members during copying or merging

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A SAMPLE IEBCOPY //MYCOPY01 JOB (J007,,,),'IEBCOPY’,CLASS=U,MSGCLASS=Y, // TYPRUN=SCAN,NOTIFY=&SYSUID //COPY01 EXEC PGM=IEBCOPY //SYSPRINT DD SYSOUT=* //SYSUT1 DD DSN=INPUT.PDS.TOBE.COPIED,DISP=SHR //SYOUT2 DD DSN=OUTPUT.PDS.WHICH.ISTOBE.CREATED, // DISP=(NEW,CATLG,DELETE),UNIT=3390,VOL=NKP900, //SYSIN DD * COPY INDD=SYSUT1,OUTDD=SYSUT2 SELECT MEMBER=(MEM1,MEM4,MEM7) /* // 11 Nov, 2003

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IEFBR14 It’s a two line program  It simply clears register15, then passing a return code 0, and then branches to the address in the register 14, which returns control to the System  Why is it a do-nothing program?  What you can do with IEFBR14? - Scratch a Dataset - Catalogue and Uncatalog a dataset - Careate and Delete datasets - As a testing utility 11 Nov, 2003

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IEBCOMPR

 Compare sequential datasets  Compare partitioned datasets

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IEHLIST  List the contents of partitioned data set directory  List entries in a VTOC  List entries in a system catalog

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IEHPROGM  To modify system control data in VTOC, data-set label, and the system catalog  Scratch/Rename a member of a PDS  Catalog or uncatalog a dataset  Build an index for GDG

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IEBGENER  Copy a sequential file  Reorganize records in a sequential file  Change the record or block length of a sequential file  Print the contents of a sequential file  Creating a library member 11 Nov, 2003

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Advanced Mainframe Concepts / Products INTRODUCTION

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Advanced Mainframe Concepts / Products Datasets JCL JES2 / JES3 SDSF CA-7 CA-VIEW IBM Fault Analyzer Change Management ENDEVOR 11 Nov, 2003

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DATASET A data set is a named collection of data that contains individual data units organized (formatted) in a specific, IBM-prescribed way and accessed by a specific access method that is based on the data set organization. Types of data set organization:  Sequential  Relative sequential  Indexed sequential and  Partitioned 11 Nov, 2003

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Types of Datasets

Physical Sequential A Physical Sequential file, DSORG=PS, is a simple file with records stored in the order that they are written. PS files are typically used for text and logs. Large PS files which are only ever required by one task at a time, are very suitable for tape. It is possible to improve the performance of PS files by striping them over several volumes, but this is only useful if they are used by concurrent tasks

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Types of Datasets (Contd.) Partitioned The minimum size of data allocation under OS/390 is 1 track, or 56,664 bytes. This means that a Physical Sequential file which contained three 80 byte records will contain 240 bytes, but occupy 56,664. A Partitioned Dataset (PDS) solves this problem by combining a lot of small files into one large container. The individual files are stored as members within the PDS. Each member must have a unique 1-8 character name.

Issues in Partitioned datasets: There are a number of issues with PDS files. When you delete a member, the space it occupied is not reused. This means that over time, the PDS will grow, and eventually fill up. The easiest way to fix this, is to list the file on ISPF option 3.4, then enter a 'Z' against it. This will compress the file, and all the deleted space will available for use. 11 Nov, 2003

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Types of Datasets (Contd.) VSAM Structures: There are 4 types of VSAM Dataset.  Key Sequence Data set  Entry Sequence Data Set  Relative Record Data Set  Linear Data Set. Virtual Sequential Access Method is discussed in the VSAM Section.

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GDG (Generation Data Group ) Generation Data Group. Collection of (z/OS non-VSAM) datasets with the same logical name (GDG Base Entry). The individual datasets are uniquely identified by the generation number which is stored as part of the dataset name. The datasets can be referenced either by the explicit generation number or the relative generation number. GDGs are useful where datasets are cycled – standard JCL can be used without having to change the dataset names for each run. 11 Nov, 2003

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JCL (Job Control Language)

JCL: Job Control Language, or JCL, is a set of control statements that provide the specifications necessary to process a job, and the series of JCL statements that make up a job is typically called a job stream.

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JES2 & JES3 A job is the execution of one or more related programs in sequence. Each individual program executed in a job is called a job step. To process a job, a Job Entry Subsystem, or JES, is used. It keeps track of jobs that enter the system, presents them to OS/390 for processing, and sends their spooled output to the correct destination. There are two versions of JES available under OS/390: JES2 and JES3. Since JES2 and JES3 are incompatible with one another, your shop should have only one or the other installed.

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JES2 & JES3 How JES2 and JES3 process jobs : Job is submitted

Job is selected for execution

Job is executed

Job’s Output is processed

Job is purged

How a job is entered into the system Jobs are created by entering JCL commands into a display terminal. Then, the jobs are stored in files on DASD. To enter, or submit, the job into the system, the terminal user issues a SUBMIT, or SUB, command. That causes JES2 or JES3 to read the job stream from the DASD file and copy it to the job queue on the JES spool. 11 Nov, 2003

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SDSF (System Display and Search Facility) System Display and Search Facility: On-line tool for programmers and operators monitoring jobs awaiting execution in the JES2 input spool queues and, most commonly, viewing the printed output of batch jobs in the Held output spool queues, to save printing it on paper. Most users can only view their own jobs, but systems programmers and operators are normally allowed to view everything, making SDSF especially useful for monitoring jobs currently executing, or the rest of the output of that seemingly endless print job. Runs in ISPF or directly in TSO without ISPF. An optional, separately priced feature of z/OS. 11 Nov, 2003

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CA - 7 What is CA-7? CA-7 is a Production control system. It’s an online, realtime, interactive system which automatically controls, schedules jobs based on the Date and time, job dependencies and available resources.

Functions of CA-7  Provides Online Scheduling facility  Selects job for execution  Submits jobs  Tracking jobs  Analyzes job execution results

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CA - View

To view the output of the Job in online. Online viewing has been implemented to significantly reduce the amount of microfiche produced by Information Services. Instead of producing microfiche, archival copies of production reports will be redirected to an online viewing tool called CAView.

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CA – View (Contd.) Online viewing represents a significant improvement over traditional microfiche for the following reasons:  reports are available immediately; no waiting for fiche delivery  online viewing has full search capabilities  reports are more secure; only authorized users are permitted to view reports  automatic records retention; CA-View will automatically delete unnecessary reports after the amount of time you specify 11 Nov, 2003

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IBM - FAULT ANALYSER  IBM Fault Analyzer for z/OS and OS/390 assists the developer in quickly analyzing and fixing application and system failures.  Helps determine the cause of failure while further providing assistance in how to resolve the problem.  Provides support for CICS® system abends, as well as MQSeries® application abends.  Supports different modes of operation: – Real-time analysis at time of abend – Batch re-analysis of faults in history file – Interactive re-analysis of faults in history file under ISPF 11 Nov, 2003

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IBM - FAULT ANALYSER (Contd.)  Facilitates expansion of messages and abend codes applicable to the analysis result.  Lets an application add its own application specific messages and abend codes to supplement those supplied by IBM.  Provides management of application abends; the fault history file helps track and manage application abends, fault reports, and associated dumps through an interactive display.  Eliminates need to recompile programs or change JCL to invoke IBM Fault Analyzer for z/OS and OS/390®.  Applies the collective knowledge of many experts to each abend.  Offers interactive re-analysis to provide programmers with the ability to increase the level of detail the analysis engine can provide after the abend has occurred. 11 Nov, 2003

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CHANGE MANAGEMENT

In the mainframe world, there are many people in a given project group. To ensure that a module / program / JCL member etc. is not changed inadvertently , we have change management teams and products in place. These personnel, with the help of the Change management products, manage various versions of a module and account for its proper movement through various stages like test, QA, production etc. 11 Nov, 2003

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ENDEVOR What is Endevor? ENDEVOR is a Change Management software product that controls, automates, and monitors the entire application development life cycle. ENDEVOR allows you to automate and control the movement of source code from development through to production (see diagram).

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ENDEVOR (Contd.) ENDEVOR gives you the ability to:  Automatically compare and track your changes against the PRODUCTION version, creating an on-line change history. This speeds up the debugging process and enables you to see exactly WHO changed it, WHAT was changed, WHEN it was changed, WHERE it changed, and HOW it was changed.  Prevent conflicting changes to the same system component.  Browse and manipulate all components relating to an application from a single screen, saving you time and ensuring that changes are complete.  Automate creation of executables.  Ensure that the source, executable, and any other form of an element (module) correspond. 11 Nov, 2003

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ENDEVOR (Contd.)

 Apply consistent procedures (including the automation of compiles, impact analysis, and standards-checking functions) to any component type, dramatically simplifying the process.  Process changes to packages and approvals online, eliminating change-related paperwork.  View or retrieve any prior level of any element. Report on element definition, content, and change history.

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Summary Slide  Classification of Computers  Mainframe Overview  MVS  Characteristics Of Mainframe  MVS – Management of User Jobs  MVS Concepts  ISPF – An Introduction  IBM Utilities – An introduction  Advanced Mainframe Concepts / Products

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THANKS

THANK YOU !

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