What is a Mainframe?

On April 7, 1964, IBM announced their System/360 mainframe. It wasn't the first mainframe, but it was the beginning of a new era, and in some ways it did become the last mainframe.
Today, IBM's zEnterprise (and specificaly either the z196 or the z114 mainframe component of it) is light years beyond its original progenitor, but you can still run programs on it that were written for System/360 mainframes - in fact, there likely are such programs still in use.

Modern IT is also light years beyond those early days of computing, with graphics, the Internet, portable computing, and many other innovations that have given the illusion that we had moved beyond the mainframe.

What actually happened was that the mainframe became the bedrock foundation for large-scale business computing for governments, financial institutions, large manufacturers and other key organizations that keep the world economy running. In fact, if you were to turn off every mainframe right now, everything I know tells me that the world economy would be grinding to a halt before the day was over.

This is not a problem, because today's mainframes are so reliable that we've been taking them for granted for decades, without even realizing that they're handling the most critical business data processing in the world, every second of every day, allowing other platforms to handle lower-criticality activities. And as long as electricity works, the mainframe looks to keep humming along, almost invisibly keeping everything else flowing smoothly as well.

But there is a problem: perception. With the exception of those who deal directly with the mainframe, it seems almost no one is aware that modern business computing is built on the approximately 10,000 mainframes and 4,000 organizations that use them to keep things running. That can lead to some poor decision making, and skewed perceptions at the highest levels - as well as everywhere else.

I intend this blog to be one source of clarity about the mainframe, its history, its current roles, and its future. I also intend to offer insights and ideas to improve the already-substantial value of mainframe computing. And, while I will write this blog as a mainframer myself, with an audience that includes other mainframers, it is my intention that it be of value and interest to everyone who is affected by mainframes - i.e. everyone.

So, let's begin with: What is a Mainframe?

Some people have claimed the mainframe has become extinct. That's clearly inaccurate.

Some have claimed that any large computer is a mainframe. I do not endorse that definition.

My definition of today's mainframe is:

A large, highly-functional business computer, descended from IBM's System/360, which is capable of running thousands (or more) of concurrent applications, serving millions (or more) of concurrent users at greater than 99% busy with 99.999% or bettter uptime and no degradation in service. It continues to be the computer that handles much of the world's most critical business data processing, with so much reliability, availability and security that it may seem invisible, but it is actually essential.