What Makes a Mainframe?

Oh, there are Apples and Windows and things that end in "x" and even a few last instances of other platforms out there that haven't quite finished going away. There are some new operating systems for mobile devices as well. One thing they all have in common is that they aren't sufficient to constitute a mainframe.

You could run them on a mainframe if you wanted, of course - it's already happening with Linux on z. But you'd have to do it on top of what already works - in the case of Linux that would mean running it on z/VM.

But, whatever you run on the mainframe, you're going to be using one of four mainframe operating systems underneath it to make it work. Those are:

1. z/OS: this is IBM's premier mainframe operating system, and the one that supports most of the business applications and data that make the mainframe a mainstay of the world economy. It is descended from a 47-year-long line of operating systems, beginning with OS/360, all of which were written specifically for IBM's System/360 hardware and its descendants.
2. z/VM: the original "virtual machine" operating system, first officially made available in 1972, this operating system allows many (or even very, very many) operating system instances to run at the same time on the same mainframe, each as if it had an entire mainframe to itself. These instances can currently be an arbitrary selection of one or more of the four mainframe operating systems in this list and/or Linux.
3. z/VSE: the frugal mainframe operating system, introduced as a stop-gap in the early days, and always lighter in functionality and pricing than z/OS and its predecessors. Those who still use it are dedicated to it, and they have insisted that IBM continue to support it.
4. z/TPF: a specialized operating system for such applications as airline reservations, and only used by a select few organizations.

You'll note right away that "z/" is at the beginning of the current names of each of these operating systems. That's in reference to the current mainframe hardware, System z®. IBM asserts that the "z" stands for "zero downtime" as distinct from the "i," "p" and "x" for the other hardware platforms they offer. The "i" and "p" now run on IBM's Power architecture while the "x" uses Intel x86 processors.

That's important, because you could run any of the above four mainframe operating systems on a non-mainframe hardware platform using emulation (one computer pretending to be another) but it wouldn't constitute a true mainframe. The strengths of IBM's mainframe hardware are essential to creating that optimized combination of factors resulting in today's mainframe.

On top of the hardware and operating systems are two software layers of what make up today's mainframe: utility or middleware software that manages and makes the mainframe run better, and applications - many of which are tried-and-proven over decades.

But wait: there's more! Today's mainframe is not an island. In fact, it backstops many of the non-mainframe activities in the organizations where it runs. By relying on the mainframe for key data and processing, applications running on every other platform - even on the zBX portion of IBM's zEnterprise System - can let the mainframe take care of the details such as security, reliability, availability, massive volume, and being a single source for important data. So the mainframe is an essential part of an ecosystem that supports the entire world.

None of the above is sufficient to make up a mainframe, however. If you took someone with no mainframe experience or culture and gave them all the above hardware and software and told them to run it, they'd almost certainly begin by failing. That's because the beating heart of what makes the mainframe work is the people and their culture.

Now, clearly, the above is barely an appetizer about what makes a mainframe. So, the next Mainframe Analytics blog entries over the coming weeks will dig into each of these areas in greater depth in order to lay the ground work for future blog entries about other things that make the mainframe work today and tomorrow, including the mainframe's constantly-improving business value, and its brilliant future.