z/OS is IBM's mainframe operating system designed to serve thousands of users concurrently processing large workloads. It uses virtual storage to allow programs to access more memory than physically available. z/OS manages real, auxiliary, and virtual storage using pages, frames, and slots to move data between storage types. Workload management balances system resources and priorities tasks to meet business goals.

1. IBM - System
z Operating
System

2. Chapter ObjectivesChapter Objectives
How z/OS differs from single user operating
system
Types of storage used by z/OS
Concept of virtual storage and its use in
z/OS
Relationship between pages frames and
slots
Characteristics of z/OS
May 2, 2014 2IBM System Z Operating System

3. About System ZAbout System Z
System Z was developed by
IBM-2000
It is mainframe computer
Operating system is
separately designed
3IBM System Z Operating SystemMay 2, 2014

4. What is z/OSWhat is z/OS
Most widely used Mainframe Operating
System
64-bit operating system
Suited for processing large workloads
for many concurrent users
May 2, 2014 4IBM System Z Operating System

5. What is Z/OSWhat is Z/OS
Designed for
Serving 1000’s of users concurrently
I/0 and numeric intensive computing
Processing very large heterogenous
workload
Running mission critical appications
securely
May 2, 2014 5IBM System Z Operating System

6. Hardware Resources ManagedHardware Resources 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
May 2, 2014 6IBM System Z Operating System

7. Features of z/OSFeatures of z/OS
Multi Programming Multi processing
OS
Program-1
Program-2
Program-3
OS
cpu1 cpu2 cpu3 cpu4
I/o
May 2, 2014 7IBM System Z Operating System

8. Concept of Virtual StorageConcept of Virtual 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.
May 2, 2014 8IBM System Z Operating System

9. TrendsTrends
System 370
System370-XA
Z Architecture
1970
24-bit os
16MB of virtual Storage
1983
31-bit os
2GB of virtual Storage
2000
64-bit os
16EB of virtual StorageMay 2, 2014 9IBM System Z Operating System

10. z/ OS Internalsz/ OS Internals
Comprises of modules, System
programs(macros),System Components.
Concepts of Multi programming and
Multi Tasking.
May 2, 2014 10IBM System Z Operating System

11. z/os Internalsz/os Internals
Manages three different kinds of storage
Real Storage
Auxiliary Storage
Virtual Storage
May 2, 2014 11IBM System Z Operating System

12. Concept of Virtual StorageConcept of Virtual Storage
Virtual Storage is an illusion created by Z/OS
Running portion of program is kept in Real
Storage, rest is kept in auxiliary storage
The range of virtual addresses that the
operating system assigns is called address
space.
Each user program is represented by address
space
May 2, 2014 12IBM System Z Operating System

13. Concept of Virtual StorageConcept of Virtual Storage
May 2, 2014 13IBM System Z Operating System

14. 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.
May 2, 2014 14IBM System Z Operating System

15. 64-Bit Address Spaces64-Bit Address Spaces
16 megabyte The “Line”
The “Bar”2 gigabytes
2 terabytes
512 terabytes
16 exabytes
0
User Private Area
Common Area
User Extended
Private Area
Shared Area
User Extended
Private Area
The “BAR”
The “LINE”
These are
storage sub
pools
used to classify
different uses
May 2, 2014 15IBM System Z Operating System

16. Synchronous Cross MemorySynchronous Cross Memory
 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
May 2, 2014 16IBM System Z Operating System

17. How Virtual Storage works?How Virtual Storage 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
May 2, 2014 17IBM System Z Operating System

18. How Virtual Storage works?How Virtual Storage works?
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
information
A frame is a 4K piece of real storage
A slot is a 4K record in a page data setMay 2, 2014 18IBM System Z Operating System

19. How Virtual Storage works?How Virtual Storage works?
May 2, 2014 19IBM System Z Operating System

20. Pages ,Frames and SlotsPages ,Frames and Slots
The 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)
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21. Pages ,Frames and SlotsPages ,Frames and Slots
May 2, 2014 21IBM System Z Operating System

22. 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
May 2, 2014 22IBM System Z Operating System

23. 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)May 2, 2014 23IBM System Z Operating System

24. 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.May 2, 2014 24IBM System Z Operating System

25. 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.
May 2, 2014 25IBM System Z Operating System

26. 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
May 2, 2014 26IBM System Z Operating System

27. Work Load ManagementWork Load Management
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
May 2, 2014 27IBM System Z Operating System

28. Work Load ManagementWork Load Management
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 TIME
May 2, 2014 28IBM System Z Operating System

29. Work Load ManagementWork Load Management
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)May 2, 2014 29IBM System Z Operating System

30. Work Load ManagementWork Load Management
Inhibits 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.
May 2, 2014 30IBM System Z Operating System

31. Interrupts ProcessingInterrupts Processing
An interrupt is an event that alters the
sequence in which the processor executes
instructions
An interrupt may be planned or unplanned
Supervisor call Interrupt External InterruptI/O Interrupt
Program InterruptRestart Interrupt
Machine check InterruptsMay 2, 2014 31IBM System Z Operating System

32. How Program Status word isHow Program Status word is
usedused
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
May 2, 2014 32IBM System Z Operating System

33. CharacteristicsCharacteristics
Uses 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.May 2, 2014 33IBM System Z Operating System

34. CharacteristicsCharacteristics
Allows 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.May 2, 2014 34IBM System Z Operating System

35. 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.May 2, 2014 35IBM System Z Operating System

36. Workload Manager-Consistent Service LevelsWorkload Manager-Consistent Service Levels
IBM System Z Operating System
36
Batch
Reporting
Data Base
Processing
OnLine
Processing
Batch File
Updating
Data
Mining
Transaction type:
ƒ Web "buy" vs "browse"
ƒ B2B
ƒ Batch payroll
ƒ Test
User/user type:
ƒ Top 100 clients
ƒ Typical clients
ƒ Executive
ƒ Design team
Time periods:
ƒ 1AM - 4AM
ƒ Mon - Fri
ƒ Weekends
ƒ End of quarter
Policy
Based
Policy
Based
S
Y
S
P
L
E
X

37. Provide ScalibilityProvide Scalibility
May 2, 2014
IBM System Z Operating System 37
37
Parallel
Sysplex
Firewalls
Routers and
Edge Servers
Web Servers
Application
Servers
Solution: + Multiply!
+ Multiply!
+ Multiply!
How quickly can more capacity be added?

38. • C:UsersARPANADesktopSemaphore and M
• C:UsersARPANADesktopOperating System
May 2, 2014 IBM System Z Operating System 38

39. May 2, 2014 39IBM System Z Operating System

40. • http://publib.boulder.ibm.com/infocenter/zos/ba
May 2, 2014 40IBM System Z Operating System