MVS ... A long and rich heritage..
A history of IBM¹s most powerful and reliable operating system
(pictures of 360 and 370 reference cards )
........ MVS: Then and now
Today, MVS is IBM¹s most powerful and reliable computer operating
system. Over the years, MVS has been refined and honed, incorporating
customer requirements, remaining attuned to new hardware and software
developments, and expanding its capabilities to keep pace with changing
directions in technology. The MVS of today is not the MVS of old. In fact,
much of MVS has been rewritten, using state-of-the-art techniques which
reflect new concepts and functions to ensure high levels of quality and
availability.
MVS/ESA(tm) has a long and rich heritage. Its roots lie in OS/360, an
IBM operating system developed in the 1960s. Whether you are a newcomer to
MVS, or have been in data processing for 40 years, we hope you enjoy
retrospective.
(Picture of AUTOCHART CODING SHEET)
OS/360
In April 1964, IBM announced OS/360, an operating system developed to
support the new generation and architecture OS System/360(tm) hardware
capable of both commercial and scientific applications. Prior to System/360,
these applications ran on separate lines of hardware.
OS/360 included three control programs options, delivered in stages
beginning in March 1966. The first stage was the simplest - a sequential
scheduler called the primary control program (PCP). PCP, performed only one
task at a time, and ran in 32KB of memory. That¹s right! Kilobytes, not
megabytes. With PCP, a processor could spend considerable time waiting for
I/O. OS/360 was the first operating system to require direct access devices.
Multiprogramming introduced the technique of assigning control of the
processor to another task while the first task was waiting for I/O. This
technique utilized resources more effectively.
Next came MFT (multiprogramming with a fixed number of tasks). Initially
MFT supported four tasks at one time. Later it was upgraded to support
fifteen tasks. A third option, MVT (multiprogramming with a variable number
of tasks) followed . Theoretically, MVT allowed any number of tasks to be
performed concurrently. Because of the added function, more real storage was
required: 64KB for MFT and 128KB for MVT.
System installation was accomplished through sysgen, a time consuming,
difficult and tedious process performed in two stages: building the system
and defining the I/O configuration. Early user requirements identified the
need to simplify this process.
Prior to OS/360, even the most dedicated programmers found I/O
programming to be a painful process - repetitive, inconsistent, and error
prone. OS/360 supplied data and telecommunications access methods that
simplified the task.
Job control language (JCL) also was introduced at this time.
Upon initial release the access methods included BSAM, QSAM, BDAM, BPAM.
In addition, OS/360 contained system utilities, an assembler, and some
compilers. Applications were soon developed that required faster access to
data. Consequently, ISAM and QTAM were added. :Later, improvements were made
to linking new functions and operational enhancements were added. A
checkpoint/restart facility was developed to allow application to restart at
points other than the beginning. However due to the limited size of the
processor storage, many applications couldn¹t be stored in one piece. An
overlay supervisor was developed to help control and load the application in
parts.
In 1968, a multi-processing capability was designed for the System/360
(S/360) Model 65. This new function was supported by MVT, and allowed a user
to have dual Model 65s, which could share central storage under control of a
single operating system. Having two processors working on the same job
significantly improved application availability.
As more and more organizations began developing compilers, users wanted
the flexibility to pick and choose among these, including IBM compilers. To
respond to this need, in 1969 IBM changed its definition of the operating
system to distinguish our compilers from system code. Compilers were
classified as program products, offered separate license agreements.
OS/360 was originally developed as a batch operating system. However,
users soon asked for interactive capability. In 1971, IBM released the
time-sharing option (TSO), which became an integral part of the operating
system. TSO used TCAM, a new communications access method that was developed
and released at the same time.
Release 21.8, the last in the OS/360 line was made available in 1974.
(Picture of a OS/360 green card)
MVS/370
?79....
Times and marketing conditions changed rapidly in the late 1970s. By
1979, the concept of pricing system code separately from the hardware was
established. Some of the first separately priced products were ACF/VTAM(tm)
and DFP/370. JES2 and JES3 were considered integral to the base control
program (BCP) and therefore were packaged with the BCP as part of MVS/SP. It
was definition time again. In the new separately priced structure, the
combination of MVS/SP and DFP/370 now made up the operating system called
MVS/370.
When OS/VS2 MVS was developed, some virtual storage was designed to be
common storage, shared by all address spaces, while some was declared
private storage, for use by applications. Our direction was to reserve
one-half of a 126MB virtual address space for use by the operating system
and the other half to be used by customer applications. At this time, common
virtual storage was used primarily by the operating system. However, IMS,
VTAM and other products were seeing the benefits of occupying common virtual
storage. Not surprisingly, it didn¹t take long before the operating system
with its subsystems exceeded its half. that left only 2-3MB for
applications. It wasn¹t long before applications learned the value of
virtual storage, eliminating overlays and simplifying design. Suddenly after
only three years, there was no more room! And we though virtual storage
would last a long time.
With the introduction of MVS/SP 1.3 a new feature, cross memory was
introduced a dual address space architecture, which provided for direct
access to programs and data in separate address space under the control of
the new cross-memory authorization mechanism. Cross-memory allowed
subsystems and server-like functions to manage data and control blocks
efficiently in private storage. Moving code from common virtual storage to
private virtual storage provided some virtual storage constraint relief
(VSCR).. For applications, as well as additional isolation and protection
for subsystem control blocks and data. IMS, VTAM, JES3 and MVS components
were among the first to use cross-memory.
Although virtual storage was limited to 16MB because of 24-bit address,
processor architecture allowed a 26-bit (64MB) address for real storage,
supported in MVS/SP 1.3. MVS/370 performance was improved by utilizing the
additional real storage as paging space.
The MVS 3.8 operating system was required as an installation base for
MVS/370. MVS 3.8 contained specific functions, such as BTAM and GAM, which
had not yet been provided as separately priced products.
MVS/370 was withdrawn from marketing in December 1991. Service was
discontinued in December 1992, approximately 13 years from original
availability.
(Picture of a System/370 Reference Summary card )
The next major evolutionary step took place in 1981, with the
introduction of the IBM 3081 processor complex with 370-XA extended
architecture. 370-XA defined a dynamic channel capability, plus 31-bit
addressing for both real and virtual storage. To support the new functions,
the MVS/SP product had to be reworked. The result was named MVS/SP Version
2. The original MVS/SP product was then renamed MVS/SP Version 1.
Technically, since both products also contained JES, the correct names were
MVS/SP-JES2 Version 1 or Version 2 and MVS/SP-JES3 Version 1 or 2.
MVS 3.8 contained five distinct data-management functions, which were
updated and repackaged into a new product, MVS/XA DFP Version 1. MVS/SP
Version 2 and MVS/XA DFP Version 1 were co-requisite products. Together they
made up the MVS/XA operating system, first made available in March of 1983.
Other licensed products, such as ACF/VTAM and ACF/TCAM were updated to work
with the new architecture. BTAM was also revised and a new licensed,
BTAM/SP was created.
Although MVS/370 provided some VSCR with cross memory, it wasn¹t enough.
A continual effort was required to maintain a balance between operating
system usage and application usage. MVS/XA with its 31-bit addressing
structure, gave access to 2 gigabytes (2GB) of virtual storage per address
space - 128 times more than MVS/370. What a relief!
New operating system code and other licensed programs moved control
block and data above the 16MB virtual, which up to that time was the highest
virtual storage address. As might be expected, the first question was ³How
long will 2GB of virtual last?² Although the architecture allowed for 2GB of
real storage, implementation in software didn¹t occur until storage of that
size was also supported by the processors.
Throughout this process, compatibility was maintained to protect our
customer investment in applications. 370-XA introduced a bi-modal addressing
capability, which allowed most applications for OS/360, OS/VS1, or OS/VS2 or
MVS/370 (24 bit address structure) to run with the MVS/XA (31-bit addressing
structure).
To aid the customer with migration to the IBM family of 308x processors,
OS/VS2, MVS 3.8 and MVS 370 all ran on the new hardware, but without the
ability to utilize the new architecture..
Dynamic channel architecture allowed access to I/O devices over any of
eight channels. Initial hardware implementation was four channels. Specific
DASD devices were able to reconnect to and pass data back on a different
channel from the one on which the request was received. Significant
improvements in channel utilization were achieved. Requests were queued and
managed by the channel rather than the operating system, freeing up
processor resources.
When the IBM ES/3090(tm) processor complex was introduced in 1985, it
contained new hardware features: vector facility, expanded storage primarily
to improve paging performance by reducing I/O that occurs when writing pages
to DASD. Along the way, MVS/XA DFP continued to add function, including
ISMF, a catalog address space, and VSCR, and was reversioned into MVS/XA DFP
Version 2.
Because of the demand for high availability, MVS/XA. Along with IMS/VS,
ACF/VTAM and ACF/NCP, introduced XRF, a capability that allowed high-speed
switching of applications and terminals to an alternate system. CICS/MVS(tm)
added similar capabilities. JES2 followed suit with a dual spooling
capability.
As a result of changing views on intellectual property and enforcement
of software copyrights and patents, MVS began distributing code as object
code-only (OCO). User exits, better documentation and improved
responsiveness to both requirements and requests for service helped to
smooth the transition from source code to object code.
As a wider selection of products became available for MVS, the pre
integrated IPO became less useful. It was a common package with a product
set that was limited to basic user needs. This meant that all optional
products had to be installed separately. In 1984, IBM introduced a custom
built IPO, which allowed users to specify products from a menu. A set of
distribution libraries, with integrated service, was then built to order.
CBIPOs were developed for new customers as well as those who wanted to
replace existing systems.
In 1986, CBPDO was introduced for those users who wanted to enhance
their existing systems with added service for all products for which the
user was licensed. As with CBIPO, new products were selected from a product
menu.
MVS/XA was withdrawn from marketing on December 31, 1992.
*****MVS/ESA
In February 1988, IBM announced ESA/370(tm), which provided new
capabilities for the IBM ES/3090 processors, including access registers,
linkage stacks and PR/SM(tm). The volume of data to be processed had risen
dramatically over the proceeding decade . Access registers made it easier to
separate application code from data, resulting in improvements in data
volume handling capabilities and data isolation. ESA/370 provided a new
virtual storage space for data only, called a data space. Unlike a cross
memory address space, no application code can execute in a data space.
Linkage stacks simplify calls/program returns between address spaces, as
well as program calls/program returns within a single address space. Linkage
stacks also offer associated recovery routines that reduce the need for
ESTAEs. Today¹s DB2(tm) uses Linkage stacks facilities.
Once again, MVS/SP V2 and MVS DFP V2 were reworked into the next level
of the MVS operating system, MVS/ESA. MVS/ESA product levels were MVS/SP
Version 3 and MVS/DFP Version 3 also contained significant productivity
enhancement called system-managed storage. System managed storage allows
the operating system to place and control data on external devices, based on
data characteristics and usage. System-managed storage significantly
improves DASD utilization, and reduces the work that people, particularly
the storage administrator, must do. MVS/DFP 3.2 provided PDSEs, a new 4K
physical blocksize structure for partitioned data sets. PDSEs eliminate
periodic compresses and the need for careful space pre-planning. MVS/DFP V3
offered a network file server, supporting Sun(tm) Microsystem¹s remote
procedure call (RPC) through TCP/IP. The network file server represented a
first functional step toward making MVS/ESA operate in an open-system
environment. MVS/DFP V3 also introduced a new access method, OAM, in support
of optical disk technology.
Data spaces addressed a long-standing customer requirement-the ability
to access and process data more quickly. Data spaces allow large amounts of
data to reside in processor storage, essentially trading storage for I/O
access time. Data in a data space is byte addressable, and can be
manipulated directly by a program in an address space. Two new services, LLA
and VLF, allow the operating system and subsystems to easily utilize data
spaces for program libraries, CLISTs and data objects.
MVS/SP V3 also provided a special high-speed form of data space called a
Hiperspace(tm). Hiperspace data always resides in expanded storage, and must
be moved to the address space for manipulation. However, it does not use the
paging mechanism. Movement in 4KB or multiples of 4KB blocks bypasses the
high-speed buffer. Since data in the high-speed buffer is not disturbed, the
buffer hit ratio is improved. VSAM LSR and DFSORT utilize Hiperspaces to
improve performance. Another storage technique, Hiperbatch(tm), allows
interim VSAM or QSAM sequential data to be kept in a Hiperspace for improved
batch processing.
Assembler and FORTRAN were subsequently updated to enable user
applications to directly access data in data spaces. Callable services are
provided so user applications can utilize Hiperspaces.
MVS/ESA SP 3.1.3 with RACF(tm) 1.8 received a B1 security rating from
the U.S. Department of Defense. B1 provides the appropriate environment for
applications that must have mandatory label security protection.
The first release of MVS/ESA was delivered in August 1988.
To provide for an orderly migration from MVS/XA to MVS/ESA, two
provisions were made. MVS/XA DFP 2.4 was updated to run with MVS/SP V3 until
such time as MVS/DFP V3 could be installed. No Hiperspace support was
available with MVS/XA DFP2.4. For users needing system-managed before
migrating to MVS/ESA, MVS/DFP V3 was upgraded to run on MVS/XA with
starter-level, system managed storage function.
OS/VS3 MVS 3.8 remained an installation prerequisite for new users of
MVS.
The continuation of MVS/ESA
In September 1990, IBM announced ESA/390(tm) and the ES/9000 family of
processors. Prime new concepts were Sysplex and ESCON(tm). Again, the base
control program was enhanced to support the new architecture, resulting in
MVS/ESA SP Version 4.
A new component, XCF was added, which allowed authorized applications on
one system to communicate via CTC with the other specified authorized
applications on another MVS/ESA SP Version 4 system. If an application or
system begins to fail, the companion application on the other system can be
called into service.
XCF presented the opportunity for higher levels of availability.
OPC(tm)/ESA, CICS/ESA(tm) XRF and JES2 V4 have been modified to utilize XCF
services for takeover and recovery. XCF can also be used with PR/SM ARF to
automatically reconfigure processor storage when takeover occurs.
Another new component, APPC/MVS, provided a new level of application
portability and interoperability with other SAA(tm) systems. APPC
applications can now operate in client server fashion and may be ported from
one operating system to another when written to the CPI-C interface.
Dynamic I/O reconfiguration was realized through ESCON architecture, the
ESCON Manager licensed product, and MVS/ESA SP4 V4 HCD. Specified
channel-attached devices can be attached and configurations changed without
bringing the system down, reducing PORs and IPLs. Support was also provided
in NCP to dynamically add preconfigured lines with HCD. A common and
consistent front end was also developed for HCD and ESCON Manager, using the
ScreenView feature. ScreenView is part of MVS/ESA SP4.3. Once again,
productivity for the systems programmer was improved.
PR/SM EMIF, an extension announced for ESA/390 in June 1992, is also
supported by MVS/ESA SP 4.3 PR/SM EMIF allows sharing of ESCON channels
among logical hardware partitions, which should increase configuration
flexibility and provide cost savings through reduction in the number of
channels required for PR/SM.
DFSMS/MVS(tm), announced in MAY 1992, integrates and expands the storage
and program management functions previously available in MVS/DFP V3, DFHSM
and DFDSS. A new feature, Removable Media Manager, was also added.
DFSMSrmm(tm) allows tapes, both automated and manual libraries, to have full
automated management support by DFSMS.
DFSMS/MVS has since added a concurrent copy function that provides
potential for improved data availability during the backup process.
DFDSM/MVS is capable to act as a file backup and archive server for LAN file
servers and workstations. It also allows applications access to local or
distributed record data of DDM systems. Remaining OS/VS2 MVS 3.8 components
were repackaged into existing licensed products and the requirement to have
MVS 3.8 as an installation base was removed with MVS/ESA SP 4.2.2.
In 1992, IBM further simplified the installation process through a group
of offerings called CustomPacs(tm). One of these, the SystemPac(tm), is a
system replacement option that goes beyond CBIPO in building and
customizing. Two others, ProductPac(tm) and ServicePac(tm), are system
upgrade options, tailored to a particular system rather than to an
establishment. They are simpler to install and require less SMP/E knowledge
than CBPDO.
Throughout the existence of MVS, heavy emphasis has been made on
reliability. With MVS/ESA SP V4, we increased our efforts to ensure quality
and reliability.. Both existing code and newly developed code were examined
for defects, and corrections included in the product. However, quality means
more than code-defect removal. Installation procedures, IPL actions,
publications and other forms of documentation were also reviewed and
updated.
MVS/ESA SP 4.3 OpenEdition(tm) services provide an expanded role for
MVS¹s participation in an open-systems environment. POSIX and OSF(r)/DCE are
currently being developed to run MVS/ESA SP 4.3. Netview(r) and DFDSM are
key products upon which MVS system management and network management will be
built. MVS/ESA will continue to play a leadership role in out customers¹
enterprises within the open-system environment. It will act as the
enterprise-wide data server and database manager; it will provide data
protection and integrity; it will be the enterprise-wide network manager,
providing upload/down-load, backup and recovery services; it will be the
base for high-volume, high-response transaction processing; an application
server; a technical computing platform; a high-volume cryptographic
platform; a data compression platform and a quality server.
Needless to say, MVS remains a superior batch processing system. The
addition of VIO to expanded storage, Hiperbatch, Batch LSR and data striping
have contributed significantly to this capability.
Future directions point to MVS support of a parallel processing
environment, providing significant improvements in data sharing and workload
balancing.
With MVS/ESA, a high degree of scaleability has been achieved, moving
from a uniprocessor environment through eight-way multiprocessing and
Sysplex; from kilobytes of real storage to gigabytes of central and expanded
storage. Additional processors are supported with efficient utilization
ratios. MVS/ESA supports the full range of architectural features.
Architecture defined-protection mechanisms range from low-address protection
for MVS to subsystem storage protection for CICS. MVS defines virtual
storage that reaches into terrabytes. It has added sort instructions, DB2
sort-assist facility, a vector facility, a cryptographic feature and
compression, data streaming channels, dynamic channel subsystems. ESCON
channels, CTCs, a Sysplex Timer(tm) and more.
MVS/ESA has evolved into a highly sophisticated and reliable operating
system - one which provides tremendous customer value and is continually
responsive to customer needs. MVS/ESA has the quality integrity and
function, along with the responsiveness and the performance realization,
required to run today¹s businesses. No other operating system matches it.
Application investments made in os/360, OS/VS2, MVS/370, MVS/XA and
earlier levels of MVS/ESA continue to work with today¹s MVS/ESA.
MVS will continue to enhance its offerings with the characteristics that
have always been its strengths-and can help companies like yours meet the
challenge of the 90¹s.
(end)
Glossary
ACF/TCAM Advanced Communication Function/TCAM
ACF/VTAM Advanced Communication Function/VTAM
APPC/MVS Advanced Program-to-Program Communication/MVS
ASP Attached Support Processor
CICS/MVS Customer Information Control System
CPI-C Common Programming Interface For Communications
BCP Base Control Program
BDAM Basic Direct Access Method
BPAM Basic Partitioned Access Method
BSAM Basic Sequential Access Method
BTAM Basic Telecommunications Access Method
BTAM/SP BTAM/System Product
CBIPO Custom Built Installation Offering
CBPDO Custom Built Product Delivery Offering
CTC Channel-to-Channel
DASD Direct Access Storage Device
DFDSM Data Facility Distributed System Management
DFP/MVS Data Facility Product/MVS
DFSMS Data Facility Storage Management Subsystem
DFSMS/MVS Data Facility Storage Management Subsystem/MVS
ESCON Enterprise System Connections
ESTAE Extended-specify Task Abnormal Exit
GAM Graphic Access Method
GB Gigabyte - 1,000,000,000 bytes
HASP Houston Automatic Spooling Program
HCD Hardware Configuration Definition
I/O Input/Output
IMS/VS Information Management System/Virtual Storage
IPL Initial Program Load
IPO Integrated Program Offering
ISAM Indexed Sequential Access Method
ISMF Interactive Storage Management
LLA Library Lookaside
LSR Local Shared Resources
MB Megabytes - 1,000,000 bytes
MVS Multiple Virtual Storage
MVS/ESA MVS/Enterprise System Architecture
MVS/SP MVS/System Product
MVS/XA MVS/Extended Architecture
OAM Object Access Method
OCO Object Code Only
OS/VS Operating System/Virtual Storage
PDSE Partitioned Data Set Extended
POR Power-on-Reset
PR/SM Processor Resource/Storage Manager
PR/SM ARF PR/SM Automatic Recovery Facility
PR/SM EMIF PR/SM ESCON Multiple Image Facility
QSAM Queued Sequential Access Method
QTAM Queued Telecommunications Access Method
SAA Systems Applications Architecture
SNA Systems Network Architecture
TCAM Telecommunications Access Method
TCP/IP Transmission Control Protocol/Internet Protocol
TSO/E Time Sharing Option/Extended
VIO Virtual Input Output
VLF Virtual Lookaside Facility
VSAM Virtual Sequential Access Method
VSCR Virtual Storage Constraint Relief
VTAM Virtual Telecommunications Access Method
XCF Cross-system Coupling Facility
XRF Extended Recovery Facility
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