system z operating system

IBM - System z Operating

System

Chapter ObjectivesChapter Objectives

How z/OS differs from single user operating system

Types of storage used by z/OSConcept of virtual storage and its use in

z/OSRelationship between pages frames and

slotsCharacteristics of z/OS

April 12, 2023 2IBM System Z Operating System

About System ZAbout System Z

System Z was developed by IBM-2000

It is mainframe computerOperating system is

separately designed

3IBM System Z Operating SystemApril 12, 2023

What is z/OSWhat is z/OS

Most widely used Mainframe Operating System

64-bit operating systemSuited for processing large workloads

for many concurrent users


What is Z/OSWhat is Z/OS

Designed forServing 1000’s of users concurrentlyI/0 and numeric intensive computingProcessing very large heterogenous

workloadRunning mission critical appications

securely


Hardware Resources Hardware Resources Managed Managed

System Console(hardware)

Master Console(z/OS)

Operator Console(z/OS)

Mainframe computer(CPU, processor

storage)

z/OS running here...

Disk storage (DASD volumes)

DASD controller

Tape drive

Tape cartridges

... Director links mainframes with DASD controllers


Features of z/OSFeatures of z/OS

Multi Programming Multi processing

OS

Program-1

Program-2

Program-3

OS

cpu1 cpu2 cpu3 cpu4

I/oApril 12, 2023 7IBM System Z Operating System

Concept of Virtual Concept of Virtual Storage Storage

z/os uses virtual storage to interact with large number of users concurrently ,while processing large workloads.

Virtual storage means that each running program can assume it has access to all of the storage defined by the architecture's addressing scheme.

Virtual storage means that each running program can assume it has access to all of the storage defined by the architecture's addressing scheme.


TrendsTrends

System 370

System370-XA

Z Architectur

e

1970

24-bit os

16MB of virtual Storage

1983

31-bit os

2GB of virtual Storage

2000

64-bit os

16EB of virtual StorageApril 12, 2023 9IBM System Z Operating System

z/ OS Internalsz/ OS Internals

Comprises of modules, System programs(macros),System Components.

Concepts of Multi programming and

Multi Tasking.


z/os Internalsz/os Internals

Manages three different kinds of storage

Real Storage

Auxiliary Storage

Virtual Storage


Concept of Virtual Concept of Virtual StorageStorage

Virtual Storage is an illusion created by Z/OSRunning portion of program is kept in Real

Storage, rest is kept in auxiliary storageThe range of virtual addresses that the

operating system assigns is called address space.

Each user program is represented by address space


Concept of Virtual Concept of Virtual StorageStorage


z/OS Address Spacez/OS Address Space

It is amount of memory collected to all possible address for computational entity.

Address space may refer to a range of either physical or virtual addresses accessible to a processor or reserved for process.


64-Bit Address Spaces64-Bit Address Spaces

16 megabyte The “Line”

The “Bar” 2 gigabytes

2 terabytes

512 terabytes

16 exabytes

0User Private Area

Common Area

User ExtendedPrivate Area

Shared Area

User ExtendedPrivate Area

The “BAR”

The “LINE”

These arestorage sub poolsused to classifydifferent uses


Synchronous Cross Synchronous Cross MemoryMemory

Evolution of virtual storage It has objectives

Move data between the virtual address

Execute one instruction located in one AS and its operands are located in other address space.

Pass control synchronously between instructions located in distinct address

spaces


How Virtual Storage How Virtual Storage works?works?

Virtual storage is divided into 1-megabyte segments composed of 4-kilobyte pages

Transfer of pages between auxiliary storage and real storage is called paging

When a requested page is not in real storage, an interruption (called a page fault) is signaled and the system brings it into real storage



z/OS uses segment, page and region tables to keep track of storage

Addresses are translated dynamically, a process called Dynamic Address Translation (DAT)

Frames and slots are repositories for a page of informationA frame is a 4K piece of real storageA slot is a 4K record in a page data set


Pages ,Frames and SlotsPages ,Frames and SlotsThe pieces of a program executing in virtual

storage must be moved between real and auxiliary storage:

A Block of Real Storage

A Block of Virtual storage

A Block of Auxiliary Storage

FRAME

PAGE

SLOT

FRAMES SLOTS

4 Kilo Bytes(4096 Bytes)


Pages ,Frames and SlotsPages ,Frames and Slots


Page StealingPage Stealing

Before an application can access any page , it should be read into a buffer pool

If a buffer pool is full, then OS must delete an existing page, before it can read the new one in.

This is called Page Stealing


Page StealingPage Stealing

z/OS tries to keep an adequate supply of available real storage frames on hand.

When this supply becomes low, z/OS uses page stealing to replenish it.

Pages that have not been accessed for a relatively long time are good candidates for page stealing.

z/OS also uses various storage managers to keep track of all pages, frames, and slots in the system:Auxiliary Storage Manager (ASM)Real Storage Manager (RSM)Virtual Storage Manager (VSM)


Role of Storage ManagersRole of Storage Managers

Real storage manager The real storage manager or RSM keeps track of the

contents of central storage.

Auxiliary storage manager The auxiliary storage manager or ASM uses the

system’s page data sets, to keep track of auxiliary storage slots.

Virtual storage manager The virtual storage manager or VSM™ responds to

requests to obtain and frees virtual storage.April 12, 2023 24IBM System Z Operating System

SwappingSwapping

In order to balance workload, z/OS uses the concept of swapping

Swapping has the effect of moving an entire address space into, or out of, real storage: A swapped-in address space is active, having

pages in real storage frames and pages in auxiliary storage slots.

A swapped-out address space is inactive; the address space resides on auxiliary storage and cannot execute until it is swapped in.


Work Load ManagementWork Load Management

WLM Manages processing of work loads in a system based on Business goals.

To accomplish this, WLM Manages the use of system resources such as processors and storage



It has three objectives

OBJECTIVE - 1

To achieve the business goals That are defined by the installation ,by automatically assigning the resources to the workloads based on their importance and goals.

This Objective is known as GOAL ACHIEVEMENT



OBJECTIVE - 2

To Achieve the optimal use of system resources from system point of view

This Objective is known as THROUGHPUT

OBJECTIVE - 3

To Achieve the optimal use of system resources from the point of the address space

This Objective is known as RESPONSE AND TURN AROUND TIMEApril 12, 2023 28IBM System Z Operating System


To balance throughput with response and turnaround time, WLM does the following:

Monitors the use of resources by the various address spaces

Monitors the system-wide use of resources to determine whether they are fully utilized

Determines which address spaces to swap out (and when)


Work Load ManagementWork Load ManagementInhibits the creation of new address spaces or

steals pages when certain shortages of central storage exist

Changes the dispatching priority of address spaces, which controls the rate at which the address spaces are allowed to consume system resources

Selects the devices to be allocated, if a choice of devices exists, in order to balance the use of I/O devices.


Interrupts ProcessingInterrupts Processing

An interrupt is an event that alters the sequence in which the processor executes

instructionsAn interrupt may be planned or unplanned

Supervisor call Interrupt External InterruptI/O Interrupt

Program InterruptRestart Interrupt

Machine check InterruptsApril 12, 2023 31IBM System Z Operating System

How Program Status word How Program Status word is usedis used

The PSW controls the order in which instructions are fed to the processor

It indicates the status of the system in relation to the currently running program

Three types of PSW’s to understand interrupt processing

Current PSW

New PSW

Old PSW


CharacteristicsCharacteristicsUses address spaces to ensure isolation of

private areas

Designed to ensure data integrity, regardless of how large the user population might be

Can process a large number of concurrent

batch jobs, with automatic workload balancing Allows security to be incorporated into

applications, resources, and user profiles.April 12, 2023 33IBM System Z Operating System

CharacteristicsCharacteristicsAllows multiple communications subsystems at

the same time

Provides extensive recovery facilities, making unplanned system restarts very rare

Can manage mixed workloads

Can manage large I/O configurations of 1000s of disk drives, automated tape libraries, large printers, networks of terminals, etc.


FacilitiesFacilities

Address spaces and virtual storage for users and programs.

Virtual storage is backed by real and auxiliary storage. Movement of programs and data between real storage

and auxiliary storage through paging. Dispatching work for execution, based on priority and

ability to execute. An extensive set of facilities for managing files stored

on disk or tape. Operators use consoles to start and stop z/OS, enter commands, and manage the operating system.


Workload Manager-Consistent Service Workload Manager-Consistent Service LevelsLevels

IBM System Z Operating System36

Batch Reporting

Data BaseProcessing

OnLine Processing

Batch FileUpdating

DataMining

Transaction type:ƒ Web "buy" vs "browse" ƒ B2B ƒ Batch payrollƒ Test

User/user type: ƒ Top 100 clientsƒ Typical clientsƒ Executiveƒ Design team

Time periods: ƒ 1AM - 4AMƒ Mon - Friƒ Weekendsƒ End of quarter

PolicyBased

PolicyBased

SYSPLEX

Provide ScalibilityProvide Scalibility

April 12, 2023IBM System Z Operating System 37

37

ParallelSysplex

Firewalls

Routers andEdge Servers

Web Servers ApplicationServers

Solution: + Multiply!+ Multiply!+ Multiply!

How quickly can more capacity be added?

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April 12, 2023 IBM System Z Operating System 38

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