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SVC IT SERVICES

TRAINING AND PRESENTATION ON

MAINFRAMES

SARAVANA KUMAR NARENDRAN

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SVC IT SERVICES

WHAT ARE THE TYPES

OF COMPUTER?

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INTRODUCTION TO MAINFRAME

Types of Computer

Micro

Mini

Mainframe

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Types of Computer

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What is Micro/PersonalComputer?

Microcomputers are designed forconsumers' personal use,are not difficult to operate.

Inall microcomputers, an operating system controls thecomputerand allows a single user to run programs. Withoutan operating system, microcomputers could not run softwareapplications

Eg:word processing,Creating/Editing photos,Browsing,playing music/videos and games whicharedesigned to work witha specific operating system

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What is Mini Computer?

A minicomputer, a term no longer much used, is acomputerofa size intermediate betweena microcomputerand amainframe.

Typically, minicomputers have been stand-alone computerssold to smalland mid-size businesses forgeneral businessapplications and to large enterprises for department-level

operations.

In recent years, the minicomputerhas evolved into the"mid-range server" and is part ofanetwork.Eg: IBM'sAS/400e

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What Is Mainframe?

Mainframe system canhandle large volumes of data

A mainframe is acomputing system that businesses use tohost the commercial databases, transaction servers, andapplications that require agreater degree of security andavailability thanis commonly found on smaller-scale

machines.

The power ofa mainframe provides computing speed andcapacity, enablingit to perform high volumes of processing.

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IBM System z9 mainframe

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Who Uses the Mainframe?

Most Fortune 1000 companies use a mainframe environment

60% ofall dataavailable on the Internet is stored onmainframe computers.

Just about everyone has used a mainframe computerat one

point oranother.(Eg:If u have used ATM to interact with yourbank account,Then you used a mainframe).

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Why to Use Mainframe?

Large-scale transaction processing

Thousands of transactions per second

Support thousands of users and application programs

Simultaneously accessing resources

Terabytes ofinformationin databases Large-bandwidthcommunications

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Mainframe Strengths

The reliability, availability, and serviceability(or RAS) ofa

computer systemh

ave always beenimportant factors in dataprocessing.Reliability:

The systems hardware components have extensive self-checkingand self-recovery capabilities. The systems

software reliability is a result of extensive testingand the

ability to make quick updates for detected problems.

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Characteristics of mainframe

1) Reliable single-thread performance, whichis essentialfor reasonable operations against a database.

2) Maximum I/O connectivity, wh

ich

means mainframesexcelat providing forhuge disk farms.

3) Maximum I/O bandwidth, so connections between drivesand processors have few choke-points.

4) Reliability--mainframes oftenallow for "gracefuldegradation" and service while the

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MAINFRAME HARDWARE RESOURSES

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Mainframe Hardware Evolution

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INTRODUCTION TO MAINFRAMEMainframe Hardware Evolution

Operating

system

Hardware Average # ofjobs running

concurrently

StorageTypes

Virtual Storage

limits

PCP System 360 1 Main Virtual Storage not available

MFT/

MVT System 360 10-20

Main Virtu

alStor

age

not

av

ailab

le

SVS System 370 30 - 50 Main

Auxiliary

16 megabytes

* Programs share addressspace

MVS/SPMVS/

Base

System 370 100s Main

Auxiliary

16 megabytes

* Each program has

its ownaddress space

MVS/XA System370/XA

1000s Main

Expanded

Auxiliary

2 gigabytes

MVS/ESA ESA/370 1000s Main

Expanded

2 gigabytes

* Addition of 2 new

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Mainframe Hardware Resourses

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Configururation of Mainframe

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Uniprocessing Vs Multiprocessing

Uniprocessing Multiprocessing

1.A Uniprocessorhas oneprocessor executing tasks.

2.Ina Uniprocessor, a singleprocess has access to storageand to the channel subsystem.

1.The term refers to the ability tohave more than one taskexecutingat the same time.

2.Its not just two or more tasksrunningin the ProcessorComplex at the same time, buttwo instructions executingat thesame point of time.

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Uniprocessing

Schematic of Uniprocessing

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Multiprocessing

Non-Partitionable

Multiprocessors Partitionable Multiprocessors

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MAINFRAME OPERATING SYSTEMS

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OS 360

OS family

In the late 1960s there were two versions of OS in wide

spread use.They are :

OS/MFT

OS/MVT

Actually they differed in the way they handledmultiprogramming.

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OS 360

MFT - Stands forMultiprogramming with fixed number of

tasks. It preallocated a fixed number of partitions where user

jobs could execute. So underMFT, the number of jobs that

could be multiprogrammed is equal to number of

preallocated partitions.

MVT Stands forMultiprogramming with variable number

of tasks, the logicis just opposite to MFT. The number of

jobs that could be multiprogrammed depends on storage

available and size of partitionis decided during run time and

it is variable.

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MVS OS-370/370XA /370ESA

MVS: (Operating System)MVS offers multiple virtual storage that means each multi-

programmed job is given its own virtual storage address spacewhich can be up to 16MB or 2GB based on our MVS version.

MVS Versions: MVS/370 Older version of MVS that limits a users address

space to 16MB. MVS/XA New version that allows up to 2GB address space

for each user.

MVS-ESA latest version ofMVS whichlet each job accessmore than one 2GB address space.

O/S 390 :IBMs OS/390 was the next generation of Operating Systems.

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O/S 390 - Z/OS

O/S 390 :

IBMs 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 groupPlans for the upgrade and converts all the current products to the

upgraded version.

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ADDRESSABLE STORAGE

Brief history of OS addressability:

1970 System/370 defined storage addresses as 24 bits inLength

1983 System/370-XA extended the addressability of thearchitecture to 31 bits.

2000 z/Architecture extended the addressability to 64 bits.

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ADDRESSABLE STORAGE

What is an Address Space?

Anaddress space is acomplete range ofaddresses

that can be accessed by a processor.

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ADDRESSABLE STORAGE

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ADDRESSABLE STORAGE

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ADDRESSABLE STORAGE

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ADDRESSABLE STORAGE

Differences between Address space and Data space

ADDRESS SPACE DATA SPACE

Contains instructionand data.

Commonareas and nucleus ismapped on Address space.

Anapplicationcanhave oneaddress space.

Cancontain only data. Evenifprogram s loaded in data space,

it is considered as data.

None ofcommonareas andnucleus is mapped on data

Space.

Anapplicationcanhave accessup to 7999 data space, each thesize of 2GB.

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Roles in the mainframe world

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Characteristic Features ofMainframe Operating Systems

The features's are:

1)Batch

processing2)Time - sharing3)Spooling4)Virtual Storage5)Multiprogramming

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Batch processing

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Online processing

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Batch vs Online/Interactive

ProcessingBatch Processing Interactive processing

Jobs are submitted for execution by theprocessorat later time.

Absence ofany interaction from user.

Performance measure is throughput.

Userinteractionis simulated by meansof system files.

Snap shot of the output is used fordebugging.

Jobs submitted are executedimmediately.

Userinteractionis a usual thing.

Performance measure is response time.

This may provide batch processing. This

processingis also knownas background

Processing.

Interactive debugging may be provided.

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DATA MANAGEMENT

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DATA MANAGEMENT

#Withina dataset, datacan be organized in one ofseveral ways

depending onhow the data will ultimately be processed we

have VSAM &NON-VSAM.

Depends on dataset purpose, file organizationisselected.

Dataset organization:

VSAM NON-VSAM

1.Entry Sequence Data Set(ESDS)

2.Key Sequence Data Set(KSDS)

3.Relative Data Set(RRDS)

4.Linear Data Sets(LDS)

1. Sequential(PS)

2. Indexed sequential

3. Direct

4. Partitioned(PDS)

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DATA STORAGE MANAGEMENT

# DASD

#MAGNETIC TAPE

# CENTRAL STORAGE

Types of Data Storage devices:

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DATA STORAGE MANAGEMENT

Mainframe memory/storage hierarchy

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DASD->Direct Access Storage Device

A group of DASDs of same type are connected together

to form a Stringand are connected to a stringcontroller.

Multiple stringcontrollerare connected to a storage

controller.

Storage controlleris connected to channel.

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Tracks & Cylinders:

> Datais recorded on the usable surfaces ofa disk pack inconcentriccircles called tracks.> The number of tracks per surface varies with each device type.> For Eg:A disk pack consisting of 19 usable surfaces, each with808 tracks has a total of 15352 tracks.> Access mechanism or Actuatoris the component that readsor4 writes data on the tracks ofa disk pack. The actuatorhas oneread/write head for each recording surface.>When the actuator moves all ofits head move together so

they are all positioned at the same track of each recordingsurface.> As a result the disk drive canaccess data onall those trackswithout moving the actuator.

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DASD-> Data format

There are two types of Data Formats:

Fixed block data format

Count Key data format (CKD format)

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DASD-> Data format

Fixed block data(FBA):# Tracks are preformatted with fixed size blocks usually 512

bytes.

# Every physical record on the track is the same size.

# If the applicationneeds smaller orlargerlogical records, theyare "fitted" into the fixed size by the operating system.

Logical record1 Logical record2 Logical record3

Physical record

32 32 32 32 32 32

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DASD-> Data format

CKD ( count-key-data) devices:# CKD architecture devices have a self-defining record structure which

allows records from approximately 18 bytes up to the full track size to

be recorded on the surface of the disk.

# Each data block preceded by acount areaand a key area (which

should be met before datain dir of rotation).Gaps to separate count,key and dataareas.

# Store datain variable-length blocks.

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MAGNETIC TAPE-> Data format

#Magnetic tape is the best storage

medium for dataand contains most of the

data that is stored in the data processing

environment.

#Magnetic tape is made by takingaplastic tape and bondingalayer of

magnetic material on the tape.

# Store data for backup purpose.

# There are two types of magnetic tape

round tapes and square tapes.

# 4 to 8 tape drives are connected to one

control unit

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Virtual Storage

How virtual storage works

Virtual storage is divided into 4-kilobytepages

Transfer of pages betweenauxiliary storage and real storage

is calledpaging.

Whena requested address is not in real storage, an

interruptionis signaled and the system brings the required page

into real storage.

z/OS uses tables to keep track of pages

Dynamicaddress translation (DAT)

Frames, pages, slots

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Virtual Storage

PAGING:-

Pagingis the physical movement of single 4K pieces ofinformationfrom the main storage toexpanded orauxiliary storage and backagain.

MVS divides virtual storage into 4K (4096bytes)sections called

pages.

Datais transferred between realand DASD storage one page at atime.

Hence real storage is divided into 4K sections calledpageframes,each of whichcanhold one page of virtual storage.

The DASD area used for virtual storage, called a page data set, isdivided into 4K (4096 bytes blocks) page slots,each of whichholdsone page of virtual storage.

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Virtual Storage

Real/Central Storage vs Virtual Storage

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Virtual Storage

Real/Central Storage vs Virtual Storage

If Then

- a 4K piece (page) of dataisrequested

- requested datais in main storage

- requested datais not in main storage

- requested datais in expandedstorage

- the system looks in main storage tosatisfy the request.

- the request is satisfied.

- a page fault occurs and the systemlooks in expanded storage for the data.

- it is paged to main storage.

- a page fault occurs and the systempages data storage into main storagefrom auxiliary storage.

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Virtual Storage

Expanded Storage:-

- System/390 or ESA processors now include a special type ofmemory called expandedstorage.

- Expanded storage improves the efficiency of virtual storageoperations by actingas alarge buffer between real storage andthe page data sets.

- Whena virtual storage page must be paged out, theprocessor moves the page's contents to expanded storage.

- This transfer occurs at CPU speeds rather thanat DASDspeeds.

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Virtual Storage

Paging Hierarchy:-- Programs and dataare moved between main, expanded and

auxiliary storage based on frequency of use.

- Programs and data must be in main storage to execute.

- Address space is created by system for user's program and

data.

- Address space is being used by OS program code and OSdata elements.

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Virtual Storage

Swapping:-- Swapingis the physical movement ofall 4K pieces of

information fora single job from main storage to expanded orauxiliary storage and back again.

- MVS periodically transfers entire address spaces inand out

of virtual storage so that they are temporarily unavailable forprocessing, whichis called swapping.

- Auxiliary Storage Manager (ASM) whichis one of theMVS/370 and MVS/XA subsystems transfers Virtual Storagepages between Central Storage and auxiliary storage either by

paging or swapping.- ASMis called by the Real Storage Manager (RSM) and bythe Virtual Block Processor (VBP).

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Virtual StorageThe concept of Swapping in Mvs

Page Data Sets Real Storage Swap Data Sets

AddressSpace 1(swappedin)




AddressSpace 5(swappedout)



CPU

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Virtual Storage

Program Modes:-- A program withinanaddress space can runis eitherreal mode or

virtual mode.

- These modes indicate whether ornot a program is subject to thepaging or swapping processes.

- Pagingand swapping operate only for programs that runinvirtual mode.

- Programs that operate in real mode are not paged or swapped.

- Some parts of the operating system are responsible formanaging virtual storage and they cannot be subjected to pagingprocess.

- These parts of the operating system are expected to be alwaysresident in real storage.So they are non-pageable ornon-swappable.

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Virtual StorageHow virtual storage works

Pages, Frames, and SlotsThe pieces ofa program executingin virtual storage must bemovedbetween realand auxiliary storage:

A block of real storage is aframe.A block of virtual storage is apage.A block ofauxiliary storage is aslot.A page, a frame, and a slot are all the same size: 4096 bytes (4kilobytes).

To the programmer, t

he entire program appears to occupycontiguous

space in real storage at all times.

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Data Access methods

Access methods:

Sequential Access Method (SAM)

Partitioned Access Method

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Sequential Access Method (SAM)

SAM files have records placed ina physical rather thanlogical order.

Sequential files are created one record after the other.

Magnetic tape, cards, and printed output are sequentialfiles.

Direct-access devices may contain sequential files.

Sequential files are usually writtenand read one after theother.

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Partitioned Access Method (PAM)

It is anaccess method forlibraries witha specificstructure, called partitioned datasets (PDS).

A PDS consists of members (that are internally identical tosequential data sets,that a membercannot be a PDS

itself)registered inalist called directory.

The combination of members and directory is a singledataset on disk.

The directory contains alist of member's names (max. 8characters) and member's addresses.

Addresses are relative to the start of the dataset in order toallow the PDS to be moved to a different disk location.

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MVS RECORD FORMATS

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MVS RECORD FORMATS

MVS has many record formats some of them are:

Fixed Unblocked(F)

Fixed Blocked(FB)Variable Unblocked(V)Variable Blocked(VB)Variable Spanned(VS)Variable Blocked(VBS)Undefined(U)

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MVS RECORD FORMATS

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MVS RECORD FORMATS

Fixed Unblocked:

` Ina fixed unblocked file, all records are of thesame length (hence "fixed").

` Each physical block contains one logical record.The physicaland logical sizes are same.

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MVS RECORD FORMATS

` In FB, each physical block contains anintegralnumber oflogicalrecords.

` Alllogical records must be the same size. Two reasons exist forblocking tape or DASD files:

- Maximize the efficiency of t

he storage media.- Eff iciently blocked files have fewergaps.

- Fewer gaps mean more of the magnetic medium is used fordata.

- Speed up data transfer.

Fixed Blocked:

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MVS RECORD FORMATS

Variable Unblocked(V):

- In this format, the records are blocked, but with only one

record per block.

- Before each record there is a 4-byte record descriptor word.

- In the first two bytes is the length of the record plus thelength of the record descriptor.

- The second two bytes contain binary zeros.

- Thus, the longest record possible is 32,756 bytes.

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MVS RECORD FORMATS

Variable Blocked(VB):- In this format the records are blocked with more than one

record per block.

- Before each record there is a 4-byte record descriptor

word.

- Each block contains as many complete records (with their

record descriptors) as can fit within the block.

- Logical records are not spanned across block boundaries.

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MVS RECORD FORMATS

Variable Spanned(VS):

- In this format, the records are blocked, but with only one record ora

part of one record per block.

- Eachnew record is placed inanew block, evenif there is space

available in the previous block.

- Each record or part ofa record is a segment. Instead of record

descriptor words, there are segment descriptor words.

- The 4-byte segment descriptor word contains a two-byte segment

lengthand segmentation flags.

- The length of the record is the sum of the lengths of the segments.Because the lengthis not written explicitly, this format supports logical

records longer than 32 KB.

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MVS RECORD FORMATS

Variable Spanned(VS):

The segmentation flags define whether the segment is:

> A complete record,

>The first part,

>The last part, or>Anintermediary part ofa record that is neither first norlast.

C1 : Block Control InformationC2 : Record or Segment Control Information

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MVS RECORD FORMATS

Variable Blocked Spanned(VBS):

- In this format, the records are blocked and records can spanblocks.

- Each record or part ofa record is a segment.

- Instead of record descriptor words, there are segmentdescriptor words.

- The 4-byte segment descriptor word contains a two-bytesegment lengthand segmentation flags.

- The length of the record is the sum of the lengths of the

segments.- Because the lengthis not written explicitly, this format supports

logical records longer than 32 KB.

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MVS RECORD FORMATS

Variable Blocked Spanned(VBS):

The segmentation flags define whether the segment is:

> A complete record,

>The first part,

>The last part, or>Anintermediary part ofa record that is neither first norlast.

C1 : Block Control InformationC2 : Record or Segment Control Information

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MVS RECORD FORMATS

Undefined(U):

- This format consists of variable-length physical records and blockswithno predefined structure.

- Although this format may appearattractive for many unusualapplications, it is normally used only for executable modules.

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VOLUME TABLE OF CONTENTS(VTOC)

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VTOC

- Z/OS uses acatalogand a volume table ofcontents (VTOC) on eachDASD to manage the storage and placement of data sets.

- The VTOC lists t

he data sets t

hat reside onits volume, along wit

hinformationabout the locationand size of each data set, and other data

set attributes.

- The ownercan specify the locationand size of the VTOC.

- The size can be quite variable, ranging from a few tracks to per

haps100 tracks, depending on the expected use of the volume.

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VTOC

Z/OS requires a particular format for disks,Eg:Record 1 onthe first track of the first cylinder provides the label for the disk.It contains the 6-character volume serial (volser) numberand apointer to the volume table of contents (VTOC), whichcan belocated anywhere on the disk.

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Storage Management Subsystem(SMS)

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Storage Management Subsystem

- Disk allocation fornew data sets is directed to the mostsuitable group of disk volumes undercentralized disk-storage administrationcontrol.

- The user does not determine which volumes will beused.

- The management ofa data set afterit is created ofarchiving, retention, etc., is also undercentralizedadministrationcontr

ol.

- JCLis simplified.

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- SMS is agroup of software products, whichautomates tasksrelated to disk storage management that were previouslyh

andled manually.- SMS is anattempt to separate the logical view from thephysical view.

- SMS is implemented throughagroup of software productscollectively referred to as DFSMS.

- It enhances the system performance, reduces datacenter

complexity and gives the application programmer more timeto develop applications.

Automating Storage Management:

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- Data Facility System Managed Storage (DFSMS) includes

tools and procedures used to automate many of the

management tasks.

- DFSMS is aconcept that is implemented with the Storage

Management Subsystem (SMS) software.

- The various components of the Data Facility System Managed

Storage (DFSMS) have been tabulated.

Managed Storage (DFSMS):

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Storage Management SubsystemManaged Storage (DFSMS)

Components of DFSMS Function

MVS / DFP: Multiple Virtual Storage /Data Facility Product

Integrates all the Storage ManagementSubsystem components.

DFHSM: Data Facility HierarchicalStorage Manager

Automates archival procedures for datasets.

DFDSS: Data Facility Data Set Services Automates backup and spacemanagement procedures for datafunctions.

DFSORT: Data Facility Sort Provides sortingand copying functions.

RACF: Resource Access Control Facility Controls access to data sets according tothe security requirements specified at thesite.

ISMF: Interactive Storage ManagementFacility

Creates and revises storagemanagement constructs.

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Job Entry Subsystems (JES)

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- The Job Entry Subsystem (JES) is the part ofMVS, which

manages batch

jobs, and SYSOUT underMVS.

- There are two types:

# JES2

# JES3

Contd..

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The Similarities between JES2 and JES3 are: Both receive batch jobs to be processed by MVS.

Instream data (SYSIN) is stored until the jobs and

OPENs/READs the file.

Both support writers to print the batch jobs from local users

and remote users of the datacenter.

They support TSO.

Both JES subsystem writes accountinginformation.

Both support remote computing - Network Job Entry.

Ability for batch jobs to submit other jobs during execution.

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# Input

#Conversion

#Execution

#Output

#Purge

JES Processing

Contd..

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Input Processing- Reads a job into the system. An"internal" readerallocated from a batch job, a startedsystem task, ora TSO session may also be used forasoftware readerinterface. Once the whole job has been

read, it is placed ona queue for the next p

hase.

Conversion Processing- The converter scans the Jobcontrollanguage (JCL) for syntax errors and creates anencoded representation of the job called internal text. Ifalllooks well, then the job is placed on the next queue: job

transmission or execution. If there is an errorcrypticmessage is included with the JCLand it goes to theOutput processor.

JES Processing

Contd..

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Execution Processing -

- JES keeps track of each job by buildinga Job Queue Element(JQE) to present the job.

- The JQE has name, the job number,the job class, the Priority,

Input, an Output routing, and pointers to othercontrol blocks.- A job class may have 1 to 38 possible classes. A-Z are the

first 26 possibilities, 0-9 are 10 more, and "Started Task" and"logon" are the 37thand 38th.

- Ifaninitiatorhas more than one job class assigned,then jobsare selected in order by job class.

- For example, ifinitiator 10 has job class "AB" assigned,class"B" jobs will be selected only if there are no class "A" job.

Contd..

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Output Processing:-- As a job produces output, Job Output Elements (JOEs) are

built.- Each unique output data set with different characteristics is

represented by JOEs are kept ina table called the JobOutput Table (JOT).

- Output data sets are written to print and punch files in theJES SPOOL.

- They can be routed to localand/or remote locations. Only

afterall spooled data sets are processed can th

e jobproceed to the purge queue.

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JES2 AND JES3 Comparison

JES2 JES3

- Non-centralized processorcomplexmanagement

- Device allocationis controlled byMVS routines

- Device allocationis done at step level

- If one JES2 fails, the work continuesin other Processor Complexes

- In JES2 controlled environment, allconsoles are MVS consoles. JES2uses MVS console services to

communicate with

operator

- Centralized management techniqueswhere one processorcomplex is theKingand other JES3 are slaves.

- The Global JES3 Processor Complexcontrols all Allocation

- Device allocationis done at JOB level

- If the JES3 Global ProcessorComplex fails, the GLOBAL must beswitched to aLocal ProcessorComplex.

- Ina JES3 environment, mostconsoles are controlled from the

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1

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1 2

S ( S)

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3

J b E t S b t (JES)

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3 4

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3 4

Purge

5

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Virtual Telecommunication Access Method

(VTAM)

WHY WE USE VTAM?

The IBM subsystem controls localand remote terminals forapplication programs orallows communication.

VTAM supports systems network arch

itecture forMVS.

The subsystems suchas TSO, CICS and IMS interface withMVS ina teleprocessing environment and the subsystemssuchas IMS and DB2 Interface withMVS ina data baseenvironment.

These subsystems use many of the facilities ofMVS, suchas multiple address spaces and Cross Memory Services.

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Virtual Telecommunication Access Method

(VTAM)

MVS

VTAM

TSO CICS

IMS

DB2 DL / I

Teleprocessing System

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ANY QUERIES???

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mvs final

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