What makes Linux standout when compared to z/OS or to rephrase, what are the additional features in Linux on the mainframe not available under MVS? z/OS and even OS/390 I believe already possess Unix like capabilities (providing TCP/IP applications, Web services, Web to CICS connectivity, etc.)?
Primarily, the major advantages to having Linux on the mainframe is -- in combination -- with the traditional IBM operating systems, not by itself. Linux is: 1. ASCII based, allowing easy portability of useful applications w/o the difficulties of porting to a non-ASCII environment. 2. Widely accepted outside the mainframe universe. This benefits both consumer and ISV in that code does not need to be dual-path for mainframe and non-mainframe environments. The same applications that run in traditional Unix environments are immediately available -- at the same level and level of function -- on the Linux platform as elsewhere. No waiting for USS ports or rewrites for z/OS. 3. Widely accepted tooling. The software development and deployment tools are the same ones used in every other Unix environment immediately making your programmers productive. These are also the tools that your new hires are likely to know without additional training. 4. ISVs are much more likely to port popular applications to Linux than z/OS or USS due to the larger potential market. If an ISV has an Intel Linux version of the application, providing a mainframe version is a matter of compiling the binaries on a 390 and testing. Producing a USS or z/OS port is much more difficult. 5. The combination of Linux on the mainframe and the traditional IBM operating systems allows Linux to quickly provide accepted industry standard access tools and methods but allow data to reside in an environment that is optimized for data management. z/OS is transaction-oriented, Linux is communications-oriented. Right tool, right job. Unix System Services (USS) is the z/OS component that provides a Unix 95 API to z/OS function. It is: 1. EBCDIC, which requires significant coding in most applications to cope with a non-contiguous character set. 2. Unfamiliar to most developers (even IBM no longer recommends USS as the native platform for z/OS apps). 3. Missing access to many z/OS function (such as tape) except through assembler programming (a rare skill for Unix programmers). 4. Non-standard API. Unix 95 may be a "standard" but it lacks acceptance in the real world. The Linux and Solaris APIs are the de-facto "standards." 5. Non-portability of code. Unless you have very skilled or disciplined programmers, code written for USS is not reusable elsewhere. In my opinion, Linux will take over a majority of the application logic and front-end access to mainframe applications due to its wide acceptance with tooling and interface toolkit vendors and z/OS will be tasked with providing a transaction and data storage/data management engine. z/VM will assume a majority of the function of LPARs (as it should have years ago!) and take over resource management and virtualization of server and network hardware.
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