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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. :)

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A cloud will never be a mainframe. They do drastically different things. – Ignacio Vazquez-Abrams May 12 '11 at 10:04
a cloud is a redundant array of inexpensive systems. A mainframe is one VERY large terribly expensive system with massive amounts of , well, everything – Journeyman Geek May 12 '11 at 10:39
Mainframes can RUN clouds. They can have thousands of virtual servers running simultaneously. – Anthony Giorgio Sep 28 '11 at 12:23

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.

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Until P2SC came along, which moved them all onto one chip. – Ignacio Vazquez-Abrams May 12 '11 at 10:28
The danger here is that I could start droning on about paper tape, mag core and 57Mb washing machines. It could all end up in a Monty Python style debate... :) – Tog May 12 '11 at 10:37

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.


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"(don't laugh)" Sorry, couldn't help it. – Ignacio Vazquez-Abrams May 12 '11 at 10:53
So my android smartphone kept under AC would also be a mainframe :) Seriously though, what about the programmers' job? I am just unable to imagine what "maintanence" means. – Rama May 12 '11 at 10:53
Your android smartphone doesn't need AC in order to function. Maintenance is the same as in any other computer, except more complicated because of having more hardware and larger programs (more lines of code), and whose original programmers have got a very good chance of not still being around. – harrymc May 12 '11 at 11:09
Any group of racks filled with rackmount kit in a server room will need HVAC though. – paradroid May 12 '11 at 11:48
@paradroid: A group of racks is not defined as "a computer". For the moment, my funny definition still holds :) – harrymc May 12 '11 at 12:20

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.


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Mainframe is made up of several multiprocessors, vector processors and Massivelly Processors(MPP) connected thru very large scale interconnected bus has the capability to process mulit-processing fuctions and to having RAM and ROM having much capibility to send and receive the Data at much hi speed. Programs in Mainframe are mostly Register oriented has multi-level programs

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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.

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This is not really all that close to correct. – Ignacio Vazquez-Abrams May 12 '11 at 10:06
Maybe in 1973 that was true, but not anymore. – Anthony Giorgio Sep 28 '11 at 12:24

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