IBM markets z/OS as its flagship operating system, suited for continuous, high-volume operation with high security and stability. However, increasing numbers of middleware products and applications, such as DB2 Version 8 and above, now require and exploit 64-bit addressing. Application programmers can still use any addressing mode: all applications, regardless of their addressing mode(s), can coexist without modification, and IBM maintains commitment to tri-modal backward compatibility.
Now z/OS is supported only on z/Architecture mainframes and runs only in 64-bit mode. (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. 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. However, modern IBM mainframes also offer two additional levels of virtualization: LPARs and (optionally) z/VM.įrom its inception z/OS has had tri-modal addressing ( 24-bit, 31-bit, and 64-bit). This capability inherently supports multi-tenancy within a single operating system image. 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. z/OS is designed for high quality of service (QoS), even within a single operating system instance, and has built-in Parallel Sysplex clustering capability.
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. These compatibilities make z/OS capable of running a range of commercial and open source software. However, z/OS also implements 64-bit Java, C, C++, and UNIX ( Single UNIX Specification) APIs and applications through UNIX System Services – The Open Group certifies z/OS as a compliant UNIX operating system – with UNIX/Linux-style hierarchical HFS and zFS file systems. Z/OS supports stable mainframe facilities such as CICS, COBOL, IMS, PL/I, DB2, RACF, SNA, IBM MQ, record-oriented data access methods, REXX, CLIST, SMP/E, JCL, TSO/E, and ISPF, among others. 2.2 z/OS Encryption Readiness Technology (zERT).History of IBM mainframe operating systems
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 ( Learn how and when to remove this template message)Ĭlosed source with open source components. ( March 2021) ( Learn how and when to remove this template message) See Wikipedia's guide to writing better articles for suggestions. This article's tone or style may not reflect the encyclopedic tone used on Wikipedia.