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Z/OS
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- "ZOS" redirects here. For the Canadian television miniseries, see ZOS: Zone of Separation.
z/OS is a 64-bit operating system for mainframe computers, created 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.
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Encyclopedia
- "ZOS" redirects here. For the Canadian television miniseries, see ZOS: Zone of Separation.
z/OS is a 64-bit operating system for mainframe computers, created 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.)
z/OS supports mainframe staple technologies such as CICS, IMS, DB2, RACF, SNA, WebSphere MQ, record-oriented data access methods, REXX, 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, with UNIX/Linux-style hierarchical HFS and zFS file systems. z/OS can communicate directly via TCP/IP, including IPv6, and includes a standard HTTP server along with other common services such as FTP, NFS, and CIFS/SMB. Another central design philosophy is support for extremely high qualities of service (QoS), even with 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 version (at least at present), releases are normally called "Release n", though more formally they are "Version 1 Release n" or "V1.n".
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. (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. Application programmers can still use any addressing mode, and all applications regardless of their addressing mode(s) can coexist without modification. 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 operating system, suited for continuous, high-volume operation with high security and stability. It is the most popular mainframe operating system.
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.
IBM reliably introduces new releases of z/OS annually, in September of each year. Release 10 became generally available on September 26, 2008 (first announced on August 5, 2008). On February 24, 2009, IBM released a preview announcement for z/OS 1.11, detailing expected new features and general availability in September, 2009.
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.)
See also
External links
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