Editing Z/OS

{{short description|64-bit operating system for IBM mainframes}}
{{redirect|ZOS|the Canadian television miniseries|ZOS: Zone of Separation|the airport|Cañal Bajo Carlos Hott Siebert Airport}}
{{Tone|date=March 2021}}
{{Lowercase title}}
{{Infobox OS
| name = z/OS
| logo = IBM logo.svg
| logo caption = 
| logo size = 120px
| screenshot = <!-- Deleted image removed:  [[File:ZOS welcome screen.png|300px]] -->
| caption = The z/OS welcome screen as seen through a [[terminal emulator]]. This classic interface is still available but [[World Wide Web|Web]] access is common.
| developer = [[IBM]]
| family = {{hlist|[[MVS]]|[[Unix]]}}
| source_model = [[Closed source]] with [[open source]] components
| released = {{Start date and age|2001|03|30}} (V1R1, announced October, 2000)
| latest_release_version = Version 3.1 (V3R1)
| latest_release_date = {{Start date and age|2023|09|29}}
| latest_test_version = 
| latest_test_date = 
| marketing_target = Enterprise / Mainframes
| programmed_in = primarily [[PL/X]], [[HLASM]], and [[C (programming language)|C]]/[[C++]]<ref>{{cite web|last1=Giorgio|first1=Anthony|title=We are the IBM z/OS development team. AUA! • r/IAmA|url=https://www.reddit.com/r/IAmA/comments/3f5x1i/we_are_the_ibm_zos_development_team_aua/ctlnqje/?context=1|website=reddit|date=30 July 2015|access-date=19 June 2017|language=en}}</ref>
| prog_language = [[Java (programming language)|Java]], [[C (programming language)|C]], [[C++]], [[COBOL]], [[PL/I]], [[HLASM]], [[FORTRAN]], [[REXX]], and many others
| language = [[English language|English]] and other languages
| kernel_type = [[Monolithic kernel|Monolithic]] (uniquely hardware-assisted)
| userland = MVS, [[UNIX System Services]]
| ui = [[ISPF]], z/OS Management Facility
| license = [[Proprietary software|Proprietary]] monthly license charge (MLC); pricing available based on actual use (VWLC, EWLC, AWLC, EAWLC, IWP); reduced pricing options (zELC, zNALC, "Solution Edition") for many applications
| working_state = Current
| supported_platforms = [[z/Architecture]]
| updatemodel = 
| package_manager = [[SMP/E]]
| website = {{URL|ibm.com/products/zos}}
}}
{{History of IBM mainframe operating systems|os_only=os_only}}

[[File:IBM System z10.jpg|thumbnail|An IBM System Z10 mainframe computer on which z/OS can run.]]

'''z/OS''' is a [[64-bit computing|64-bit]] [[operating system]] for [[IBM]] [[z/Architecture]] [[Mainframe computer|mainframes]], introduced by IBM in October 2000.<ref>Vijayan, Jaikumar. "Z/OS: Users Expect Big Savings." ''[[Computerworld]],'' 19 November 2001, Vol. 35 Issue 47, p. 40</ref> It derives from and is the successor to [[OS/390]], which in turn was preceded by a string of [[MVS]] versions.<ref group="NB">Starting with the earliest:

* OS/VS2 Release 2 through Release 3.8
* MVS/System Extensions (MVS/SE)
* MVS/System Product (MVS/SP) Version 1
* MVS/System Product Version 2 (MVS/Extended Architecture, [[MVS/XA]])
* MVS/System Product Version 3 (MVS/Enterprise Systems Architecture, MVS/ESA)
* MVS/ESA SP Version 4
* MVS/ESA SP Version 5
</ref> Like OS/390, z/OS combines a number of formerly separate, related products, some of which are still optional. z/OS has the attributes of modern operating systems but also retains much of the older functionality that originated in the 1960s and is still in regular use—z/OS is designed for [[backward compatibility]].

==Major characteristics==
<!-- No, z/OS does not implement, e.g., CICS, COBOL DB2, IMS, MQ, PL/I. -->
z/OS supports<ref group=NB>Some, e.g., TSO/E, are bundled with z/OS, others, e.g., CICS, are separately priced.</ref> stable mainframe facilities such as [[CICS]], [[Common Business-Oriented Language|COBOL]], [[IBM Information Management System|IMS]], [[PL/I]], [[IBM Db2]], [[IBM Resource Access Control Facility|RACF]], [[Systems Network Architecture|SNA]], [[IBM MQ]], record-oriented data [[access methods]], [[REXX]], [[CLIST]], [[SMP/E]], [[Job Control Language|JCL]], [[Time Sharing Option|TSO/E]], and [[ISPF]], among others.

z/OS also ships with a 64-bit [[Java (programming language)|Java]] runtime, [[C (programming language)|C]]/[[C++]] compiler based on the [[LLVM]] open-source [[Clang]] infrastructure,<ref>{{Cite web |title=IBM z/OS XL C/C++ {{!}} IBM |url=https://www.ibm.com/products/xl-cpp-compiler-zos |access-date=2023-12-04 |website=IBM |language=en-us}}</ref> and UNIX ([[Single UNIX Specification]]) APIs and applications through [[UNIX System Services]]&nbsp;– [[The Open Group]] certifies z/OS as a compliant UNIX operating system&nbsp;– with UNIX/Linux-style hierarchical [[Hierarchical File System (IBM MVS)|HFS]]<ref group="NB">Not to be confused with the [[Classic Mac OS|Macintosh]] [[Hierarchical File System (Apple)|HFS]]</ref><ref group="NB">IBM has dropped HFS starting with z/OS Version 2 Release 5.</ref> and [[zFS (z/OS file system)|zFS]]<ref group="NB">Not to be confused with [[ZFS]]</ref> [[file systems]]. These compatibilities make z/OS capable of running a range of commercial and [[open-source software]].<ref>{{Cite web |url=http://www.oss4zos.org/ |title=Main Page - Oss4zos |access-date=2009-12-21 |archive-date=2008-07-04 |archive-url=https://web.archive.org/web/20080704064024/http://www.oss4zos.org/ |url-status=dead }}</ref> z/OS can communicate directly via [[Internet protocol suite|TCP/IP]], including [[IPv6]],<ref>{{cite web |url=https://www.ibm.com/products/zos-communications-server |title=IBM z/OS Communications Server |website=IBM|date=24 April 2024 }}</ref> and includes standard [[HTTP server]]s (one from [[Lotus software|Lotus]], the other [[Apache Foundation|Apache]]-derived) along with other common services such as [[SSH]], [[FTP]], [[Network File System (protocol)|NFS]], and [[CIFS]]/SMB. z/OS is designed for high [[quality of service]] (QoS), even within a single operating system instance, and has built-in [[IBM Parallel Sysplex|Parallel Sysplex]] clustering capability.

z/OS has a [[Workload Manager]] (WLM) and dispatcher which automatically manages numerous concurrently hosted units of work running in separate key-protected address spaces according to dynamically adjustable goals. This capability inherently supports multi-tenancy within a single operating system image. However, modern [[IBM mainframes]] also offer two additional levels of virtualization: [[LPAR]]s and (optionally) [[z/VM]].

From its inception z/OS has had tri-modal addressing ([[24-bit computing|24-bit]], [[31-bit computing|31-bit]], and [[64-bit computing|64-bit]]). Up through Version 1.5, z/OS itself could start in either 31-bit [[ESA/390]] or 64-bit [[z/Architecture]] mode, so it could function on older hardware, albeit without the ability to run 64-bit applications on those machines. (Only the newer z/Architecture hardware manufactured starting in the year 2000 can run 64-bit code.) IBM support for z/OS 1.5 ended on March 31, 2007, and since then, z/OS is supported only on z/Architecture mainframes and runs exclusively in 64-bit mode. Application programmers can still use any addressing mode: all applications, regardless of their addressing mode(s), can coexist without modification, and IBM maintains a commitment to tri-modal backward compatibility. However, increasing numbers of [[middleware]] products and applications, such as DB2 Version 8 and above, now require and exploit 64-bit addressing.

IBM markets z/OS as its flagship operating system,<ref>{{cite web |url=http://www-03.ibm.com/systems/z/integration/advantages.html |website=IBM |title=Why System z for Business Integration? |archive-url=https://web.archive.org/web/20060513124158/http://www-03.ibm.com/systems/z/integration/advantages.html |archive-date=2006-05-13 |url-status=dead}}</ref>  suited for continuous, high-volume operation with high security and stability.

z/OS is available under standard license pricing and via IBM Z New Application License Charges (zNALC) and "IBM Z Solution Edition", two lower-priced offerings aimed at supporting newer applications ("new workloads").<ref>{{cite web |url=https://www.ibm.com/docs/en/zos/3.1.0?topic=pricing-more-about-znalc |title=More about zNALC pricing |website=IBM}}</ref> U.S. standard commercial z/OS pricing starts at about [[US$]]125 per month, including support, for the smallest zNALC installation running the base z/OS product plus a typical set of optional z/OS features.

z/OS introduced Variable Workload License Charges (VWLC)<ref>{{cite web|title=Workload License Charges (WLC)|website=[[IBM]] |url=https://www.ibm.com/docs/en/zos/2.5.0?topic=metrics-workload-license-charges-wlc}}</ref> and Entry Workload License Charges (EWLC)<ref>{{cite web|title=Entry Workload License Charges (EWLC)|website=[[IBM]] |url=https://www.ibm.com/docs/en/zos/2.5.0?topic=metrics-entry-workload-license-charges-ewlc}}</ref> which are sub-capacity billing options. VWLC and EWLC customers only pay for peak monthly z/OS usage, not for full machine capacity as with the previous OS/390 operating system. VWLC and EWLC are also available for most IBM software products running on z/OS, and their peaks are separately calculated but can never exceed the z/OS peak. To be eligible for sub-capacity licensing, a z/OS customer must be running in [[64-bit computing|64-bit]] mode (which requires [[z/Architecture]] hardware), must have eliminated OS/390 from the system, and must e-mail IBM monthly sub-capacity reports. Sub-capacity billing substantially reduces software charges for most IBM mainframe customers.<ref>{{cite web |url=https://www.ibm.com/docs/en/zos/3.1.0?topic=level-zos-planning-sub-capacity-pricing |title=Abstract for Planning for Sub-Capacity Pricing |website=IBM}}</ref> Advanced Workload License Charges (AWLC) is the successor to VWLC on mainframe models starting with the [[zEnterprise 196]], and EAWLC is an option on [[zEnterprise 114]] models. AWLC and EAWLC offer further sub-capacity discounts.

==Other features==

===64-bit memory support===
z/OS supports 64-bit addresses for both virtual<ref>{{cite book
 | title       = z/OS 2.5 MVS Programming: Extended Addressability Guide
 | id          = SA23-1394-50
 | date        = 2021-09-30
 | section     = Chapter 4. Using the 64-bit address space
 | section-url = https://www.ibm.com/servers/resourcelink/svc00100.nsf/pages/zOSV2R5sa231394/$file/ieaa500_v2r5.pdf#page=79
 | url         = https://www.ibm.com/servers/resourcelink/svc00100.nsf/pages/zOSV2R5sa231394/$file/ieaa500_v2r5.pdf
 | pages       = 59–91
 | publisher   = [[IBM]]
 | access-date = January 6, 2023
 }}
</ref> and real addresses.
Within each address space, z/OS typically permits the placement of only data, not code, above the 2&nbsp;GB "bar". z/OS enforces this distinction primarily for performance reasons. There are no architectural impediments to allowing more than 2&nbsp;GB of application code per address space. IBM has started to allow Java code running on z/OS to execute above the 2&nbsp;GB bar, again for performance reasons.

Starting with z/OS version 2 release 3, code may be placed and executed above the 2&nbsp;GB "bar". However, very few z/OS services may be invoked from above the "bar".

Memory is obtained as "Large Memory Objects" in multiples of 1&nbsp;MB (with the expectation that applications and middleware will manage memory allocation within these large pieces). There are three types of large memory objects:

* Unshared – where only the creating address space can access the memory.
* Shared – where the creating address space can give access to specific other address spaces.
* Common – where all address spaces can access the memory. (This type was introduced in z/OS Release 10.)

===z/OS Encryption Readiness Technology (zERT)===
z/OS Encryption Readiness Technology (zERT) monitors, records, and reports details of z/OS cryptographic network protection. It is a feature of z/OS V2R3 (and later releases) Communications Server component.<ref>{{cite web|title=Things you should know about z/OS Encryption Readiness Technology (zERT) |date=31 December 2019|url=https://community.ibm.com/community/user/ibmz-and-linuxone/blogs/flora-gui1/2019/12/31/things-about-zert}}</ref>

====zERT discovery====

With zERT, the TCP/IP stack acts as a focal point in collecting and reporting the cryptographic security attributes of IPv4 and IPv6 application traffic that is protected using the TLS/SSL, SSH and IPSec cryptographic network security protocols. The collected connection level data is written to SMF in new SMF 119 subtype 11 records for analysis.<ref>{{cite web|title=z/OS Encryption Readiness Technology (zERT)|website=[[IBM]] |url=https://www.ibm.com/docs/en/zos/2.5.0?topic=zert-zos-encryption-readiness-technology}}</ref>

====zERT aggregation====

In certain environments, the volume of SMF 119 subtype 11 records can be large. The zERT aggregation function provides an alternative SMF view of the collected security session data. This alternate view is written in the form of new SMF 119 subtype 12 records that summarize the use of security sessions by many application connections over time and which are written at the end of each SMF interval. This alternate view condenses the volume of SMF record data while still providing all the critical security information.

====IBM zERT Network Analyzer====

z/OS Management Facility (z/OSMF) is enhanced to provide a plug-in named IBM zERT Network Analyzer. IBM zERT Network Analyzer is a web-based graphical user interface that z/OS network security administrators can use to analyze and report on data reported in zERT Summary records. With the zERT Network Analyzer, a z/OS network security administrator (typically a systems programmer with responsibility over z/OS Communications Server) can import SMF zERT summary records into a Db2 for z/OS database and then build and run custom queries against that data.

===Generation Data Group===
The z/OS Generation Data Group (GDG) is a description of how many generations of a file are to be kept and at what age a generation will be deleted. Whenever a new generation is created, the system checks whether one or more obsolete generations are to be deleted.

The purpose of GDGs is to automate archival, using the command language [[Job Control Language|JCL]], the file name given is generic. When [[Data set (IBM mainframe)|DSN]] appears, the GDG name appears along with the history number, where

(0) is the most recent version

(-1), (-2), ... are previous generations

(+1) a new generation (see DD)

Another use of GDGs is to be able to address all generations simultaneously within a JCL script without having to know the number of currently available generations. To do this, you have to omit the parentheses and the generation number in the JCL when specifying the dataset.

====Example====
Creation of a standard GDG for five safety scopes, each at least 35 days old:
<syntaxhighlight lang="jcl">
//STEP1 EXEC PGM=IDCAMS
//SYSPRINT DD SYSOUT=*
//SYSIN DD *
DEFINE GDG (NAME('DB2.FULLCOPY.DSNDB04.TSTEST') LIMIT(5) SCRATCH FOR(35))
/*
</syntaxhighlight>

Delete a standard GDG:
<syntaxhighlight lang="jcl">
//STEP3 EXEC PGM=IDCAMS
//SYSPRINT DD SYSOUT=*
//SYSIN DD *
DELETE DB2.FULLCOPY.DSNDB04.TSTEST GDG FORCE
/*

</syntaxhighlight>

=== Operational data collection and analysis ===
Operational data is data that z/OS system produces when it runs. This data indicates the health of the system and can be used to identify sources of performance and availability issues in the system. IBM Z Operational Log and Data Analytics and IBM Z Anomaly Analytics with Watson collect IT operational data from z/OS systems, analyze and provide insights about the operational data.

IBM Z Operational Log and Data Analytics collects IT operational data from z/OS systems, transforms it to a consumable format, and streams it to third-party enterprise analytics platforms like the Elastic Stack and [[Splunk]], or to the included operational data analysis platform. The included insights can help to visualize and search operational data to help identify the cause of operational issues.<ref>{{cite web |url=https://www.ibm.com/products/z-log-and-data-analytics |website=IBM |title=IBM Z Operational Log and Data Analytics Product Page|date=16 May 2024 }}</ref>

IBM Z Anomaly Analytics with Watson collects IT operational data from z/OS systems, uses historical IBM Z metric and log data to build a model of normal operational behavior, then analyzes real-time operational data through comparison with the model of normal operations to detect anomalous behavior, and notifies IT operations of the anomalous behavior to identify incidents that might lead to business disruption.<ref>{{cite web |url=https://www.ibm.com/products/z-anomaly-analytics |website=IBM |title=IBM Z Anomaly Analytics with Watson Product Page|date=27 June 2024 }}</ref>

==== Operational data types ====
IBM Z Operational Log and Data Analytics collects and analyzes both structured and unstructured data, including the following types of operational data:<ref>{{cite web |url=https://www.ibm.com/docs/en/z-logdata-analytics/5.1.0?topic=overview-z-common-data-provider |website=IBM |title=IBM Z Operational Log and Data Analytics documentation}}</ref>

* [[IBM System Management Facilities|System Management Facilities]] (SMF) data
* Log data from the following sources:
** Job log, the output which is written to a data definition (DD) by a running job
** z/OS UNIX log file, including the UNIX System Services system log (syslogd)
** Entry-sequenced Virtual Storage Access Method (VSAM) cluster
** z/OS system log (SYSLOG)
** IBM Tivoli NetView for z/OS messages
** [[IBM WebSphere Application Server]] for z/OS High Performance Extensible Logging (HPEL) log
** z/OS Resource Measurement Facility (RMF) Monitor III reports
* User application data, the operational data from users' own applications

IBM Z Anomaly Analytics with Watson collects data from multiple IBM Z systems and subsystems, including [[IBM Db2]] for z/OS, IBM CICS Transaction Server for z/OS and [[IBM MQ]] for z/OS.<ref>{{cite web |url=https://www.ibm.com/docs/en/z-anomaly-analytics/5.1.0 |website=IBM |title=IBM Z Anomaly Analytics with Watson documentation}}</ref> The following types of operational data are collected: 
* [[IBM System Management Facilities|System Management Facilities]] (SMF) data
* z/OS system log (SYSLOG)

==See also==
* [[OS/360 and successors#Timeline]]
* [[Fujitsu MSP]]
* [[HiperDispatch]]
* [[Hitachi VOS3]]
* [[Intelligent Resource Director]]
* [[Linux on IBM Z]]
* [[IBM Parallel Sysplex|Parallel Sysplex]]
* [[Resource Measurement Facility]]
* [[SDSF]]
* [[IBM System Management Facilities|SMF]]
* [[SMP/E]]
* [[Transaction Processing Facility|z/TPF]]
* [[IBM WebSphere Application Server|WebSphere Application Server]]
* [[Workload Manager]]
* [[zAAP]], a specialty processor dedicated to particular z/OS workloads
* [[zIIP]], another specialty processor dedicated to particular z/OS workloads
* [[VSE (operating system)|z/VSE]] for another mainframe operating system

==Notes==
{{Reflist|group=NB}}

==References==
{{Reflist|30em}}

==Further reading==
*{{cite book|author-first=Franz|author-last=Lanz|year=2015|title=IBM z/OS ISPF Smart Practices: Volume 1: User's Guide|publisher=[[De Gruyter]]|isbn= 978-3110375480}}
*{{cite book|author-first=Franz|author-last=Lanz|year=2015|title=IBM z/OS ISPF Smart Practices: Volume 2: ISPF Programmer's Guide|publisher=[[De Gruyter]]|isbn=978-3110407532}}
*{{cite book|author-first=Dinesh D.|author-last=Dattani|year=2013|title=IBM Mainframe Security: Beyond the Basics – A Practical Guide from a z/OS & RACF Perspective|publisher=MC Press|isbn=978-1583478288}}
*{{cite book|author1-first=Michael|author1-last=Teuffel|author2-first=Robert|author2-last=Vaupel|year=2010|title=Das Betriebssystem z/OS und die zSeries: Die Darstellung eines modernen Großrechnersystems|publisher=[[Walter de Gruyter]]|isbn=978-3486598780|language=DE}}
*{{cite book|author1-first=Paul|author1-last=Herrmann|author2-first=Wilhelm Gustav|author2-last=Spruth|year=2012|title=Einführung in z/OS und OS/390: Web-Services und Internet-Anwendungen für Mainframes|publisher=[[Walter de Gruyter]]|isbn=978-3486719765|language=DE}}

==External links==
* [https://www.ibm.com/products/zos Official IBM z/OS website]
* [https://www.ibm.com/support/pages/lifecycle/search?q=z%2Fos Z Product Life Cycle Policy]
* [http://www.ibm.com/software/shopzseries IBM: Shop zSeries (ShopZ)]
* [https://web.archive.org/web/20161028103549/http://www-03.ibm.com/systems/z/os/zos/library/bkserv/index.html?S_TACT=105AGX12&S_CMP=LP IBM: z/OS Internet Library]
* [http://ibmsystemsmag.com/mainframe/ IBM Systems Mainframe Magazine] {{Webarchive|url=https://web.archive.org/web/20150206122315/http://ibmsystemsmag.com/mainframe/ |date=2015-02-06 }}

{{IBM operating systems}}

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[[Category:IBM mainframe operating systems]]
[[Category:Proprietary operating systems]]