1.mf introduction

8/3/2019 1.MF Introduction

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INTRODUCTION TOMAINFRAMES


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Evolving architecture


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Early/New


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Characteristics

Centralized control of resources.

Hardware and operating systems that can share access to disk drives.

work with hundreds or thousands of simultaneous I/O operations.

Parallel Sysplex.

Perform large-scale transaction processing.

Handle large-bandwidth communication

Support thousands of users and application programs concurrently


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z/OS and other mainframeoperating systems

z/Virtual Machine (z/VM).

z/Virtual Storage Extended (z/VSE).

Linux for S/390 (uses 31-bit addressing and 32-bitregisters).

Linux for zSeries (uses 64-bit addressing andregisters).

The z/Transaction Processing Facility (z/TPF).


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Mainframe Hardware central processor complex(CPC).

CPC The physical collection of hardware thatincludes main storage, one or more central

processors, timers, and channels.

Parallel Sysplex configurations.

logical partition (LPAR) defined as an image orserver.


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Early system design


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Current Design


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System control and partitioning


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Continue

The IBM mainframe can be partitioned into separate

logical computing systems. System resources(memory, processors, I/O channels) can be dividedor shared among many such independent logical

partitions (LPARs) under the control of the LPARhypervisor, which comes with the standardProcessor Resource/Systems Manager (PR/SM)feature on all mainframes. The hypervisor is a

software layer to manage multiple operatingsystems running in a single centralprocessing complex.


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ContinueThe mainframe uses a Type 1 hypervisor. Each

LPAR supports an independent operating system(OS) loaded by a separate initial program load (IPL)operation.

Many years there was a limit of 15 LPARs in amainframe; Todays machines can be configuredwith up to 60 logical partitions. Practical limitations ofmemory size, I/O availability, and available

processing power usually limit the number ofLPARs to less than these maximums. Each LPAR isconsidered an isolated and distinct server thatsupports an instance of an operating system (OS).


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Processor Resource/SystemsManager (PR/SM)


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Characteristics of LPARs Logical partitions are, in practice, equivalent to

separate mainframes. Each LPAR runs its ownoperating system.

The system administrator can assign one or

more system processors for the exclusive use oan LPAR.

here is an implementation using a SYStemcomPLEX (SYSPLEX) where LPARs cancommunicate and collaborate sharingresources.


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ClusteringClustering has been done on mainframes since the

early S/360 days.

A clustering technique can be as simple as a sharedDASD configuration where manual control orplanning is needed to prevent unwanted data overlap.

three levels of clustering:

Basic Shared DASD.CTC rings.Parallel Sysplex.


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Basic shared DASD

RESERVE/RELEASE: commands toprotect their data sets for the duration of

the application.


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CTC rings

CTC connection A connection between two CHPIDson the same or different processors, either directly or

through a switch.


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What is a sysplex?A Systems Complex, commonly called a sysplex, is one

or more (up to 32) systems joined into a cooperativesingle unit using specialized hardware and software. Ituses unique messaging services to exchange statusinformation and can share special file structures

contained within Coupling Facility (CF) data sets.

Parallel Sysplex A sysplex that uses one or moreCoupling Facilities.

Coupling Facility A special logical partition thatprovides high-speed caching, list processing, and

locking functions in a sysplex.


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Sysplex


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Parallel Sysplex


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z/OSz/OS is designed to take advantage of the IBM System z

architecture, or z/Architecture, which was introduced in theyear 2000. The z in the name was selected because thesesystems often have zero downtime.

Hardware resources used by z/OS:


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Control blocksAs programs execute work on a z/OS system, they keep track ofthis work in storage areas called control blocks. Controls blocks

contain status data, tables,or queues.

In general, there are four types of z/OS control blocks:System-related control blocks

Resource-related control blocksJob-related control blocksTask-related control blocks

Central storage Physical storage on the processor.

Auxiliary storage Physical storage external to the mainframe,including storage on direct access devices, such as disk drivesand tape drives.


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z/OS operating environment


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Virtual storagez/OS uses both types of physical storage (central and auxiliary)

to enable another kind of storage called virtual storage. In z/OS,each user has access to virtual storage, rather than physicalstorage. This use of virtual storage is central to the unique abilityof z/OS to interact with large numbers of users concurrently,while processing the largest workloads.

There is another form of storage called expanded storage(ESTOR). Expanded storage was offered as a relativelyinexpensive way of using high speed processor storage to

minimize I/O operations. Since the introduction of z/OS with 64-bit addressing, this form of storage was not required anymore,but other operating systems, such as z/VM, still use it.


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Continue.An address space describes the virtual storage addressing

range available to a user or program.

The address space is an area of contiguous virtual addressesavailable to a program (or set of programs) and its data

requirements. The range of virtual addresses available to aprogram starts at 0 and can go to the highest address permittedby the operating system architecture. This virtual storage isavailable for user code and data.

The auxiliary storage manager controls the use of page andswap data sets. z/OS moves programs and data between centralstorage and auxiliary storage through processes called pagingand swapping.


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How virtual storage addressingworks in z/OS:


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64-bit addressability


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Additional software products forz/OS

Security system.

Compilers.

Relational database.

Transaction processing facility.

Sort program.

A large variety of utility programs.

Java virtual machines.

XML processing functions.


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Batch and Online


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Batch processingBatch processing The running of jobs on the mainframe

without user interaction.

Batch processes have the following characteristics:

Large amounts of input data are processed andstored (perhaps terabytes or more), large numbers ofrecords are accessed, and a large volume of output isproduced.

A scheduled batch process can consist of theexecution of hundreds or thousands of jobs in a pre-established sequence.


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Batch use


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ContinueAt night, numerous batch jobs running programs and utilities

are processed. These jobs consolidate the results of the onlinetransactions that take place during the day.

The batch jobs generate reports of business statistics.

Backups of critical files and databases are made before andafter the batch window.

To enable the processing of a batch job, z/OS professionals

use job control language or JCL to tell z/OS which programsare to be executed and which files will be needed by theexecuting programs.


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Online ProcessingOnline transaction processing (OLTP) Transaction

processing that occurs interactively with the end user.

Online transactions have the following characteristics:

A small amount of input data, a few stored records accessedand processed, and a small amount of data as output.

Immediate response time, usually less than one second.

Large numbers of users involved in large numbers oftransactions.


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Continue


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Transaction A unit of work performed by one or moretransaction programs, involving a specific set of input data andinitiating a specific process or job.


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How do we interact with z/OSz/OS is ideal for processing batch jobsworkloads

that run in the background with little or no humaninteraction. However, z/OS is just as much aninteractive operating system as it is a batch processingsystem. By interactivewe mean that end users(sometimes tens of thousands of them concurrently inthe case of z/OS) can use the system through directinteraction, such as commands and menu style user

interfaces.

TSO(Time Sharing Option)


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ContinueTime Sharing Option/Extensions (TSO/E) allows users to createan interactive session with the z/OS system.

TSO provides a single-user logon capability and a basic commandprompt interface to z/OS.

Most users work with TSO through its menu-driven interface,Interactive System Productivity Facility (ISPF).

3270 emulation: The use of software that enables a client to

emulate an IBM 3270 display station or printer, and to use thefunctions of a host system.


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Using TSO commands in nativemode

Native Mode: Using TSO without its complementary programs,such as ISPF.

Native TSO is similar to the interface offered by the native DOS

prompt.

With native TSO, it is possible to place a list of commands, calleda command listor CLIST.

Another command language used with TSO is called RestructuredExtended Executor or REXX. Both CLIST and REXX offer shellscript-type processing.


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ISPFISPF: A facility of z/OS that provides access to many of thefunctions most frequently needed by users.


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z/OS UNIX interactive interfaces

ISHELL,OMVS


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Record Formats


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What is a PDSE?A PDSE is a partitioned data set extended. It consists of a directory and

zero or more members, just like a PDS. It can be created with JCL, TSO/E,and ISPF, just like a PDS, and can be processed with the same accessmethods. PDSE data sets are stored only on DASD, not on tape.

The directory can expand automatically as needed, up to the addressing

limit of 522,236 members. It also has an index, which provides a fast searchfor member names. Space from deleted or moved members is automaticallyreused for new members, so you do not have to compress a PDSE toremove wasted space.

Each member of a PDSE can have up to 15,728,639 records. A PDSE

can have a maximum of 123 extents, but it cannot extend beyond onevolume.


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What is a VTOC

VTOC A structure that contains the data setlabels.


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JESJES: A collection of programs that handles the batch

workload on z/OS.

JES handles the following aspects of batch processingfor z/OS:

Receiving jobs into the operating system.Scheduling them for processing by z/OS.Controlling their output processing.

Spooling The reading and writing (by JES) of inputand output streams on auxiliary Storage devices,concurrently with job execution.


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Continue


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Spool


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JES2 compared to JES3


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common run-time environment

P il li k dit d


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Program compile, link-edit, andexecution

1.mf introduction

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