What exactly is a mainframe and what exactly does a programmer do on that?

Question

I have searched (googled) a lot but nothing answers me clearly. From what I get, "huge" computers with "many" CPUs running "legacy" software written in "legacy" languages are mainframes and the programmers "maintain" them.

I am confused. Firstly, could a cloud be considered a mainframe or if I built a system with 23 cpus with oodles of RAM and disk space would it be a mainframe? And what about the programmer's job?

So here I come to this place that has a reputation of giving quick and relevant replies. Please explain. :)

Answer 1

The mainframes I used to work on allocated CPU priority levels and RAM to dumb terminals which, in effect, acted like computers in their own right. In this way, many users could run programmes on the same computer without interfering with each other. The mainframe hardware consisted of several PCBs, each with it's own function. The central processor could consist of more than one board e.g. registers, arithmetic logic unit, floating point processor, etc.

Answer 2

Have a look at this excellent answer by Jeff Shattock to a smiliar question.

Also, I think that would be called a cluster rather than a mainframe.

Answer 3

Wikipedia's official definition is to be found in Mainframe computer.

A few decades ago, a mainframe was simply a non-portable computer, sitting in its own cupboard with all its peripherals around as well as air-conditioning. But these physically large computers did not have even the computing power of today's notebooks.

Since then, these large mainframe CPUs were replaced by multi-CPU frames, sitting (again) in their air-conditioned cupboard.

Finally (don't laugh), my own definition for a mainframe would be : "A non-portable computer requiring air-conditioning". In my opinion, air-conditioning is left as the only reliable identifier for a mainframe.

As regarding "legacy" languages, many of them are still much more in use today than "modern" languages. COBOL still makes the world go around, not C++. You should define these simply as "languages that were invented a few decades ago". Many of these got quite a few face-lifts in the meantime, so today are not all that antiquated.

Answer 4

I've always referred to, as do the programmers around me that work on it, a mainframe being our IBM iSeries. A main server (we have 2) with remote stations connecting to it as terminals. In our environment, the remote terminals are Windows XP Embedded thin clients running IBM iSeries Access and the programming language used on the iSeries is RPG.

From the very little I understand, it ships with more processors than we use (CPU on demand) - jobs can be batched and assigned a priority. This is a the typical green screen banks use, although we use all 16 colors to make things easier to read and we have some mouse click functionality in the screen.

We're in the process of migrating to a new one, that came in its own IBM branded rack (the old one was just a standing floor model).

iSeries Access is just a glorified telnet program (I've connected to it over telnet via my Mac) and my website connects to it via ODBC. Aside from iSeries Access (being a windows program) there is no GUI. Its all what looks like a command prompt. iSeries Navigator exists, but we don't use it (this would be the closest to a GUI that we have)

I've worked for 2 banks in the past and they all used some form of machine like this from IBM. Before we purchased this new rack, we considered moving to a blade system but that would have required much more migration time than we liked. Our iSeries admin ust to work for a casino and they had an entire room dedicated to multiple rack systems. In our industry, there is 1 other competitor, and its Intel based. Our application is written in house and was written for IBM and RPG.

The "i" is a class - theres are others; zSeries comes to mind.

-Mario

Answer 5

I consider a mainframe any big system that relies on the client-server/terminal model. That is there is a big computer which does all the computations and terminal for each user which only serves to connect to the mainframe.