Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 1
Chapter 17
Introduction to
IBM mainframes
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 2
Objectives
Knowledge
 Identify the three basic components of an IBM mainframe
processor.
 Identify the main difference between the z/Architecture found on
IBM’s zSeries processors and earlier system architectures.
 Name and briefly describe four types of I/O devices that are
commonly found on an IBM mainframe.
 Describe these five features of mainframe computer operating
systems: virtual storage, multiprogramming, spooling, batch
processing, and time sharing.
 Describe how MVS, OS/390, and z/OS are related to one another.
 Name three subsystems or facilities that are commonly found on
an OS/390 or z/OS system.
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 3
The basic processor architecture for IBM
mainframe systems
Main
Storage
Channel 0
Channel 1
Channel 2
Channel 3
Channel 4
Channel 5
Channel 6
Channel 7
CPU
I/O
devices
Processor
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 4
The basic architecture of an IBM mainframe
processor
 The central processing unit, or CPU, contains the circuitry
needed to execute program instructions that manipulate data
stored in main storage.
 The cache is a high-speed memory buffer that operates between
the CPU and main storage. The most frequently accessed sections
of memory are kept in the cache to speed up processing.
 Channels connect the processor to input/output devices, thus
providing access to communication networks and stored data.
 Multiprocessor systems have more than one CPU sharing access
to main memory.
 Multiprocessing can increase the overall instruction processing
rate of a system. It can also increase a system’s availability
because if one CPU fails, another can take over its work.
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 5
IBM processor history
Architecture evolution
 The ESCON architecture introduced in the System/390s improves
on earlier systems by allowing for a higher-speed information flow
between the processor and I/O devices that can be connected to the
processor over long distances.
 The z/Architecture on the zSeries processors uses a 64-bit
addressing technology rather than 31-bit addressing to allow for an
unprecedented level of memory addressing.
System/360
(S/360)
processors
ES9000
processors
S/390
G5/G6
servers
3080/4300
processors
System/370
(S/370)
processors
System/390
(S/390)
processors
zSeries
z900
servers
3090
processors
1964
1970
1980's
1985
1986
1990 2000
1998/99
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 6
I/O devices that connect to mainframe servers
 Direct access storage devices, or DASD
 Tape drives
 Optical disk devices
 Display stations
 Printers
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 7
Terminal display devices
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 8
Connecting to terminal display devices
 The 3270 family of terminal display devices has been the standard
for IBM mainframe computers since 1971.
 Although 3270s can be connected to a mainframe directly, they’re
usually connected remotely via a 3174 controller.
 Today’s typical user connects to the mainframe via a PC running
some form of 3270 emulation software. This software interprets
3270 data streams sent through a network and constructs a 3270
display screen, usually in a window on the PC’s desktop.
 In a local area network (LAN) or a wide area network (WAN),
several emulation software programs are available depending on
whether you’re connected to an SNA, Novell, or TCP/IP network.
 In an Internet or intranet environment, you can use a Telnet
(TN3270) based emulator, connect to a Citrix server that in turn
connects to the mainframe, or use a Java-enabled web browser to
display a 3270 screen.
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 9
Direct access storage devices
 The official IBM term for a disk drive is direct access storage
device, or DASD.
 A DASD allows a mainframe server direct and rapid access to
large quantities of data.
 DASD devices are attached to a server in groups called DASD
arrays.
 A storage controller manages the flow of information between the
DASD devices and the mainframe server by providing high-speed
cache storage for the data that’s accessed most frequently.
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 10
Printers
 Line printers, or impact printers, produce printed output by
striking an image of the characters to be printed against a ribbon,
which in turn transfers ink to the paper. Some line printers can
print up to 2000 lines per minute (lpm).
 Character printers, or dot-matrix printers, create character images
by causing a series of small pins in the print head to strike a
ribbon, which in turn transfers ink to the paper. They’re slower
than line printers, with some models capable of producing only
300 to 600 characters per second (cps).
 Page printers, or laser printers, produce one page at a time on
individual sheets of paper. These printers vary in size from
desktop models to full duplex systems capable of printing up to
2000 or more ipm (impressions per minute).
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 11
Magnetic tape devices
 Magnetic tapes are primarily used to back up information from
DASD and to archive older information.
 Tape processing can only be used to store and retrieve sequential
data.
 Although reel-to-reel tapes were once predominant, today it’s
more common to use tape cartridges. They can store more
information, are more durable, and process information much
faster.
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 12
Optical disk devices
 Information that is infrequently used or traditionally stored on
paper or microfiche can be stored instead on optical disks.
 Most optical drives provide WORM (Write-Once, Read-Many)
support, which produces an unalterable copy of the data onto an
optical media disk.
 Optical storage library systems store optical disks in slots that are
retrieved by robotic arms and placed in a drive reader.
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 13
An overview of virtual storage and multiprogramming
Program A
Program B
Program C
CPU
Mainframe system
Virtual storage
Real storage
(main storage)
Disk storage
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 14
Virtual storage
 Virtual storage is a technique that lets a large amount of main
storage be simulated by a processor that actually has a smaller
amount of main, or real, storage.
 The processor creates virtual storage by using disk storage to
simulate and extend real storage.
 The current program instruction being executed and any data it
requires have to be in real storage. But other data and instructions
can be placed in virtual storage and recalled into real storage
when needed.
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 15
Multiprogramming
 Multiprogramming allows more than one program to be executed
by the processor at the same time.
 Multiprogramming works because many programs spend a large
percentage of their time idle waiting for I/O operations to
complete. With multiprogramming, the system can move on to the
next program and use its CPU time more effectively.
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 16
How the operating system spools output from
application programs
Printed output
Program A
“printed” output
Program B
“printed” output
Program C
“printed” output
File for program A
output
Spooling disk
Output to
printer
Mainframe system
File for program B
output
File for program C
output
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 17
Spooling
 Spooling manages printer output for programs.
 With spooling, the output that’s directed to a printer by a program
is intercepted and directed to disk instead. Then, when the
program is finished, the operating system collects the spooled
output and sends it to the printer.
 In a multiprogramming environment, each program’s spooled
output is stored separately on disk so it can be printed separately.
 Since spooling print output to disk is faster than actually printing
the output, programs finish faster and therefore free up the
processor for other activities.
 The operating system program that handles spooling is
multiprogrammed just as the application programs are.
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 18
How batch processing works
Mainframe system
CPU
Job scheduler
JOB 1
JOB 3
JOB 2:
Program A
Program B
Program C
JOB 1:
Program A
Program B
JOB 2:
Program A
Program B
Program C
JOB 3:
Program A
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 19
Batch processing
 Batch processing is used to execute one or more programs in a
specified sequence with no further interaction by a user.
 Batch work is processed in units called jobs. Each job can contain
one or more programs to be executed.
 Job Control Language, or JCL, describes a job by providing
information that identifies the programs to be executed and the
data to be processed.
 A system’s job scheduler controls the execution of all jobs
submitted for processing, deciding which job should be executed
next based on JCL specifications and system settings.
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 20
Multiple users in a time sharing environment
Mainframe system
Running
order entry
program
Running
order entry
program
Creating
JCL for
batch job
Developing
application
program
User 1 User 2 User 4 User 3
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 21
Time sharing
 In a time sharing system, multiple users interact with the
computer at the same time.
 Each user in a time sharing environment accesses the system
through a terminal device using commands that are processed
immediately. As a result, time sharing is often called online or
interactive processing.
 Time sharing also allows users to share access to the same
application or systems programs.
 The systems programs that control time sharing are themselves
running as batch jobs in the multiprogramming environment.
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 22
The evolution of the OS/390 and z/OS operating
systems
The continuity of the operating system
 MVS, or Multiple Virtual Storage, makes up the core of today’s
OS/390 and z/OS operating systems.
 The basic forms of JCL statements haven’t changed much since
the original OS was introduced in the mid-1960s.
OS
(Operating
System)
for S/360
MVS/XA
MVS/ESA
version 5
OS/VS1
OS/VS2
(SVS)
OS/MFT
OS/MVT
MVS/ESA
version 1
OS/390 MVS/370
1964
1960's 1974
1983
1988
2001 1994
z/0S
1970's
1995
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 23
The DOS/VSE, VM, and Linux operating systems
 DOS, or Disk Operating System, was released in the 1960’s and
was designed to run on smaller systems. The current version is
called VSE/ESA and runs on S/390 servers.
 VM, or Virtual Machine, originated in 1972. It enables the
simulation of more than one computer system on a single
mainframe, with each virtual machine running under its own
operating system. A version called z/VM runs on zSeries servers.
 Linux is a UNIX-like operating system developed by Linus
Torvalds, after whom it is named. Linux on zSeries is the newest
of the operating systems designed for zSeries servers.
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 24
A partial listing of the base services offered by
OS/390 and z/OS
 Base Control Program (BCP or MVS)
 Workload Manager (WLM)
 Systems Management Services
 Application Enablement Services
 OS/390 UNIX System Services
 Distributed computing services
 Communication Server
 LAN Services Network Computing Services
 Network File System (NFS)
 Softcopy Services
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 25
New features in z/OS version 1, release 2 and
beyond
 HiperSockets
 TCP/IP Networking enhancements
 Internet and Intranet Security enhancements
 Distributed Print
 New File System and C++ compiler
 Intelligent Resource Director (IRD)
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 26
Components of the OS/390 and z/OS operating
systems
 OS/390 transformed MVS into a server operating system by
combining more than 30 products that were separate in the MVS
environment.
 Besides providing for features that are required in today’s servers,
this packaging of components was designed to simplify system
installation and to enable the products to work together more
efficiently.
 Besides the base services that are included with OS/390 and z/OS,
IBM also offers optional features that are separately priced.
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 27
Typical products in an OS/390 or z/OS environment
Product Description
JES  The Job Entry Subsystem (JES) keeps track of jobs and
their output as they’re processed by the system. There are
two versions of JES: JES2 and JES3.
TSO/E  TSO/E (Time Sharing Option/Extended), often referred to
just as TSO, is a subsystem that lets terminal users invoke
system facilities interactively.
ISPF  ISPF (Interactive System Productivity Facility) provides a
menu-driven, full-screen interface to most of TSO’s
facilities. A part of ISPF called PDF is used to develop
source programs and the JCL to compile and run them.
CICS  CICS (Customer Information Control System) makes it
possible for the system to run interactive programs
written in COBOL, PL/I, assembler language, C, C++, or
Java.
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 28
Typical products in an OS/390 or z/OS environment
(continued)
Product  Description
DB2  DB2 (Database 2) is a database management system.
It manages relational databases that can be accessed
using SQL (Structured Query Language).
Utility programs The operating system provides a set of general-
purpose utility programs to perform such functions
as copying files and sorting file records.
VTAM  VTAM (Virtual Telecommunications Access Method)
provides centralized control over all of the terminal
devices attached to the system.
RACF  RACF (Resource Access Control Facility) ensures
that a user has the correct authority to access system
resources and facilities.
Murach’s Mainframe COBOL
© 2004, Mike Murach & Associates, Inc.
Chapter 17, Slide 29
Typical products in an OS/390 or z/OS environment
(continued)
Product  Description
SMS  SMS (Storage Management Subsystem) is an
automated storage management system that removes
many of the manual procedures associated with
managing data sets.
WLM  WLM (Workload Manager) allows you to define
performance goals, then monitors system processes
and allocates system resources accordingly.
Websphere  Websphere is a Java-based application server designed
to enable e-business transactions. It supports servlets,
JavaServer Pages (JSPs), and Enterprise JavaBeans
(EJBs).
UNIX System
Services
UNIX System Services allow OS/390 to run UNIX
applications and process files from UNIX systems.