z/OS / z os basics / z os versions:
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z/OS is a 64-bit operating system for mainframe computers, produced by IBM. It is the successor to OS/390, which in turn followed MVS and combined a number of formerly separate, related products. z/OS offers the attributes of modern operating systems but also retains much of the functionality originating in the 1960s and each subsequent decade that is still found in daily use. (Extreme backward compatibility is one of z/OS's central design philosophies.) It is derived from OS/390 and was introduced in October, 2000.
z/OS supports staple mainframe technologies such as CICS, IMS, DB2, RACF, SNA, WebSphere MQ, record-oriented data access methods, REXX, CLIST, SMP/E, JCL, TSO/E, and ISPF. However, z/OS also supports 64-bit Java, C/C++, and UNIX (Single UNIX Specification) APIs and applications — The Open Group certifies z/OS as a compliant UNIX operating system — with UNIX/Linux-style hierarchical HFS (not to be confused with the Macintosh HFS) and zFS file systems. As a result, z/OS hosts a broad range of commercial and open source software. z/OS can communicate directly via TCP/IP, including IPv6, and includes standard HTTP servers (one from Lotus, the other Apache-derived) along with other common services such as FTP, NFS, and CIFS/SMB. Another central design philosophy is support for extremely high quality of service (QoS), even within a single operating system instance, although z/OS has built-in support for Parallel Sysplex clustering.
z/OS has a unique 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 business goals. This capability inherently supports multi-tenancy within a single operating system image. However, modern IBM mainframes also offer two additional levels of virtualization: LPARs and (optionally) z/VM. These new functions within the hardware, z/OS, and z/VM — and Linux and OpenSolaris support — have encouraged development of new applications for mainframes. Many of them utilize the WebSphere Application Server for z/OS middleware.
Because there is only one z/OS version (at least at present), releases are normally called "Release n," though more formally they are "Version 1 Release n" or "V1.n". The IBM Program Number for all z/OS Version 1 releases is 5694-A01.
From its inception z/OS has supported tri-modal addressing (24-bit, 31-bit, and 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 supporting 64-bit applications. (Only 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. Now z/OS is only supported on z/Architecture mainframes and only runs in 64-bit mode. z/Architecture hardware always starts running in 31-bit mode, but current z/OS quickly changes to 64-bit mode and will not run on hardware that does not support 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 an unwavering commitment to tri-modal backward compatibility. However, increasing numbers of middleware products and applications, such as DB2 Version 8 and above, now exploit 64-bit addressing.
IBM markets z/OS as a flagship[3] operating system, suited for continuous, high-volume operation with high security and stability. It is the most popular mainframe operating system.[citation needed]
z/OS is available under standard license pricing as well as via System z New Application License Charges (zNALC), a lower priced offering aimed at supporting newer applications ("new workloads"). U.S. standard commercial z/OS pricing starts at about $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) and Entry Workload License Charges (EWLC) which are sub-capacity billing options. VWLC and EWLC customers only pay for peak 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. To be eligible, a z/OS customer must be running in 64-bit mode (which requires z/Architecture hardware), must have completely 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.[6] AWLC is the comparable successor to VWLC on mainframe models starting with the zEnterprise 196.
Features
==========
64-bit memory support
========================
Within each address space, z/OS only supports the placement of data above the 2GB "bar," not code. (This distinction is enforced primarily for performance reasons. There are no architectural impediments to allowing more than 2GB of application code per address space.) Memory is obtained as "Large Memory Objects" in multiples of 1MB (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.)
Release history
==================
IBM reliably introduces new releases of z/OS each year in September. Release 11 became generally available in September, 2009.[7]
IBM supports z/OS release coexistence and fallback on an "N+2" basis. For example, IBM customers running Release 9 can upgrade directly to Release 11 (or Release 10), and both releases can operate concurrently without conflict using the same datasets, configurations, security profiles, etc. (coexistence). If there is a problem with Release 11, the customer can return to Release 9 without experiencing dataset, configuration, or security profile compatibility problems (fallback) until ready to try moving forward again. z/OS customers using Parallel Sysplex (clustering) can operate N+2 releases (e.g. Release 9 and Release 11, or Release 9 and Release 10) in mixed release configurations, in production, as long as required to complete release upgrades. (Supported software release mixing within server clusters is extremely rare among operating systems and middleware generally but routine with z/OS.) IBM's standard support period for each release is three years, so, combined with z/OS's uniquely rigorous coexistence and fallback commitments, IBM's customers routinely maintain z/OS release currency with few or zero service interruptions and without paying extended support fees. Most z/OS customers take full advantage of the N+2 support and skip every other release. Thus most z/OS customers are either "odd" or "even."
IBM releases individual patches (a.k.a. PTFs) for z/OS as needed, when needed. IBM labels critical PTFs as "HIPER" (High Impact PERvasive). IBM also "rolls up" multiple patches into a Recommended Service Update (RSU). RSUs are released periodically (in the range of every one to three months) and undergo additional testing. Although z/OS customers vary in their maintenance practices, IBM encourages every z/OS customer to adopt a reasonable preventive maintenance strategy, to avoid known problems before they might occur. z/OS customers that install periodic RSUs sometimes include the RSU information in their release description — for example, "We are running z/OS Version 1 Release 10 with RSU0909..
===================================
z/OS is a 64-bit operating system for mainframe computers, produced by IBM. It is the successor to OS/390, which in turn followed MVS and combined a number of formerly separate, related products. z/OS offers the attributes of modern operating systems but also retains much of the functionality originating in the 1960s and each subsequent decade that is still found in daily use. (Extreme backward compatibility is one of z/OS's central design philosophies.) It is derived from OS/390 and was introduced in October, 2000.
z/OS supports staple mainframe technologies such as CICS, IMS, DB2, RACF, SNA, WebSphere MQ, record-oriented data access methods, REXX, CLIST, SMP/E, JCL, TSO/E, and ISPF. However, z/OS also supports 64-bit Java, C/C++, and UNIX (Single UNIX Specification) APIs and applications — The Open Group certifies z/OS as a compliant UNIX operating system — with UNIX/Linux-style hierarchical HFS (not to be confused with the Macintosh HFS) and zFS file systems. As a result, z/OS hosts a broad range of commercial and open source software. z/OS can communicate directly via TCP/IP, including IPv6, and includes standard HTTP servers (one from Lotus, the other Apache-derived) along with other common services such as FTP, NFS, and CIFS/SMB. Another central design philosophy is support for extremely high quality of service (QoS), even within a single operating system instance, although z/OS has built-in support for Parallel Sysplex clustering.
z/OS has a unique 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 business goals. This capability inherently supports multi-tenancy within a single operating system image. However, modern IBM mainframes also offer two additional levels of virtualization: LPARs and (optionally) z/VM. These new functions within the hardware, z/OS, and z/VM — and Linux and OpenSolaris support — have encouraged development of new applications for mainframes. Many of them utilize the WebSphere Application Server for z/OS middleware.
Because there is only one z/OS version (at least at present), releases are normally called "Release n," though more formally they are "Version 1 Release n" or "V1.n". The IBM Program Number for all z/OS Version 1 releases is 5694-A01.
From its inception z/OS has supported tri-modal addressing (24-bit, 31-bit, and 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 supporting 64-bit applications. (Only 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. Now z/OS is only supported on z/Architecture mainframes and only runs in 64-bit mode. z/Architecture hardware always starts running in 31-bit mode, but current z/OS quickly changes to 64-bit mode and will not run on hardware that does not support 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 an unwavering commitment to tri-modal backward compatibility. However, increasing numbers of middleware products and applications, such as DB2 Version 8 and above, now exploit 64-bit addressing.
IBM markets z/OS as a flagship[3] operating system, suited for continuous, high-volume operation with high security and stability. It is the most popular mainframe operating system.[citation needed]
z/OS is available under standard license pricing as well as via System z New Application License Charges (zNALC), a lower priced offering aimed at supporting newer applications ("new workloads"). U.S. standard commercial z/OS pricing starts at about $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) and Entry Workload License Charges (EWLC) which are sub-capacity billing options. VWLC and EWLC customers only pay for peak 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. To be eligible, a z/OS customer must be running in 64-bit mode (which requires z/Architecture hardware), must have completely 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.[6] AWLC is the comparable successor to VWLC on mainframe models starting with the zEnterprise 196.
Features
==========
64-bit memory support
========================
Within each address space, z/OS only supports the placement of data above the 2GB "bar," not code. (This distinction is enforced primarily for performance reasons. There are no architectural impediments to allowing more than 2GB of application code per address space.) Memory is obtained as "Large Memory Objects" in multiples of 1MB (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.)
Release history
==================
IBM reliably introduces new releases of z/OS each year in September. Release 11 became generally available in September, 2009.[7]
IBM supports z/OS release coexistence and fallback on an "N+2" basis. For example, IBM customers running Release 9 can upgrade directly to Release 11 (or Release 10), and both releases can operate concurrently without conflict using the same datasets, configurations, security profiles, etc. (coexistence). If there is a problem with Release 11, the customer can return to Release 9 without experiencing dataset, configuration, or security profile compatibility problems (fallback) until ready to try moving forward again. z/OS customers using Parallel Sysplex (clustering) can operate N+2 releases (e.g. Release 9 and Release 11, or Release 9 and Release 10) in mixed release configurations, in production, as long as required to complete release upgrades. (Supported software release mixing within server clusters is extremely rare among operating systems and middleware generally but routine with z/OS.) IBM's standard support period for each release is three years, so, combined with z/OS's uniquely rigorous coexistence and fallback commitments, IBM's customers routinely maintain z/OS release currency with few or zero service interruptions and without paying extended support fees. Most z/OS customers take full advantage of the N+2 support and skip every other release. Thus most z/OS customers are either "odd" or "even."
IBM releases individual patches (a.k.a. PTFs) for z/OS as needed, when needed. IBM labels critical PTFs as "HIPER" (High Impact PERvasive). IBM also "rolls up" multiple patches into a Recommended Service Update (RSU). RSUs are released periodically (in the range of every one to three months) and undergo additional testing. Although z/OS customers vary in their maintenance practices, IBM encourages every z/OS customer to adopt a reasonable preventive maintenance strategy, to avoid known problems before they might occur. z/OS customers that install periodic RSUs sometimes include the RSU information in their release description — for example, "We are running z/OS Version 1 Release 10 with RSU0909..
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