Z/OS
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- The title of this article is incorrect because of technical limitations. The correct title is z/OS.
z/OS is a 64-bit server operating system from IBM. It is the successor to the IBM mainframe operating system OS/390, combining MVS and UNIX System Services (a POSIX-compliant mainframe implementation of UNIX formerly known as MVS Open Edition).
While assiduously retaining many features, functions, and interfaces harking back to the 1970s and even 1960s, z/OS also offers many of the same attributes and elements of so-called open systems. So while CICS, IMS, RACF, SNA, and the like are still available and in daily use, they are less the focal point for new applications than in years past. z/OS now also runs Java, supports UNIX (Single UNIX Specification) APIs and applications, and easily communicates with TCP/IP and the Web. A complementary IBM product, z/VM, improves Linux support on the same system. This combination of cutting edge functionality within z/OS and concurrent Linux support has thoroughly modernized the mainframe.
z/OS is also capable of running in 31-bit (ESA/390) mode on pre-z/Architecture mainframes. However, starting with z/OS V1R6, introduced on September 24, 2004, z/OS requires a 64-bit zSeries server. (IBM will support z/OS V1R5 until at least March 31, 2007.)
z/OS is IBM's flagship operating system, well-regarded for its ability to support mission-critical, continuous, high volume business and government operations with the utmost in security and reliability.