What in the heaven Mainframe exactly is?

[Abhishek Awasthi]

Hi,

I really mean the question. And on my part it is very funny actually. I am a programmer in Mainframe have already learnt maifnrame concepts, learned COBOL, JCL, DB2 and CICS too but I have never really understood what exactly is a mainframe.

And the boaest about it, Mainframes can't be hacked! The question is, "why mainframe can not be hacked?"

What is so special about it? And why it is still being used?

[Robert Sample]

To some degree, a mainframe is whatever a vendor declares to be a mainframe. Back in the early days (1960's and 1970's) there were a number of mainframe manufacturers including GE, Univac, Burroughs, NCR, Control Data, and Honeywell. Now, the term "mainframe" typically is applied to system z architecture machines from IBM, although I have seen the term used for Univac machines and IBM's AS/400. Broadly, a mainframe is a system designed for continuous use by hundreds (or thousands) of people simultaneously. It is special because it is widespread (something like 90%+ of Fortune 500 companies have at least one mainframe, and if you use an ATM anywhere in the world, there was, last I heard, a 95% chance that your data would be on a mainframe at some point) and long-lived (the first S360 came out in 1964; it is not unusual for mainframe programs to run 20 or 30 years without updates -- try running a Windows program from 15 years ago and see how far you get).

I would not say that the mainframe cannot be hacked -- I would say that a mainframe is hundreds or thousands of times harder to hack than a Unix or Windows machine. The hardware and software is different enough that techniques commonly used on Windows and Unix machines won't work on mainframes. Specialized knowledge is required to even begin to hack a mainframe, and then you have to be able to get access through the security package before you could start changing system code. z/OS is designed from the start to prevent hacking so it requires an exceptionally clever person to be able to bypass some of the controls in place.

[Abhishek Awasthi]

Broadly, a mainframe is a system designed for continuous use by hundreds (or thousands) of people simultaneously.

This is available in a client/server architecture too for windows, so are they be equivalent to a mainframes or can be called mainframes...if vendor decided to call the set-up as mainframes?

[Robert Sample]

You are comparing apples to elephants. Client/server is a NETWORK architecture, as opposed to the MACHINE architecture of a mainframe. A mainframe can be a server in the network, but there is no way you could describe client/server as a mainframe since mainframes are single machines. Client/server came about partly in an attempt to replicate the strengths of a mainframe without having to spend so many millions of dollars for a single box. Thin clients, when used, are pretty much the mainframe's 3270 dumb terminal, just transplanted to a client/server network.

[Abhishek Awasthi]

But "mainframe server" seems to be a usual term with many of the employees I have met...

[Robert Sample]

If your only frame of reference is desktops, laptops, and data center servers then it makes sense to call a mainframe a server (which it is, in a sense). It would be wrong to call an Intel server a "mainframe server" as the term mainframe implies capabilities an Intel machine cannot match. A single z13 IBM system, for example, can run over 8000 instances of Linux using up to 10 terabytes of memory (which, in turn, is a small fraction of the 16 exabytes of addresses available) and 141 processors simultaneously. Mainframe disk systems support as much as 1.3 petabytes (that is 1,300,000 gigabytes) of storage.

[enrico-sorichetti]

as usually people keep confusing the what it is with the what it does

what it does
I would not define a mainframe running a single image zOS as a server
but I would it define it as a server if it ran zVM with 8000 zLinux instances

what it is
but it would be always a MAINFRAME

[Abhishek Awasthi]

So it is mainframe, I mean definitions are intermixed mostly if not completely... ..