Lets start with some facts about IBM mainframes and specifically zSeries.
The hardware is brand spanking shiny and new. It contains some of the most advanced electronics and chip designs available and they are fast.
While z/OS has its roots in the 1960s it has undergone continual development and at least two complete re-writes so apart from the quirks resulting from IBM's fetish for backward compatibility its probably one of the newer OSes in general use.
The key selling points are:-
- The aforementioned backward compatibility if it a program ran in 1976 on an MVS/MVT machine the chances are it will run on the latest zSeries without being re-compiled and produce exactly the same results.
- Bandwidth it can move access and store massive amounts of data, at massive speed and at a very fine grained level.
- Availability. SYSPLEX which has been available for the last 15 years or so provides seamless clustering over multiple sites, complete with load balancing, automatic fail over etc. much of which is implemented in hardware. It makes most *nix clustering look primitive.
- Convergence. This one sounds a bit weird but with full POSIX support and a superfast JVM a modern mainframe is practically indistinguishable from any other *NIX box if that's how you want to use it.
So far the mainframe has outlived nearly everything that the pundits said were going to replace it.
There are a number of downsides:-
- Backward compatibility means that many shops are running twenty, thirty and in some cases forty year old systems. While they work well and perform their business functions well (or they wouldn't still be running!) they reflect the coding styles and obsessions of a bygone age.
- backward culture. Programmers working in a ghetto of ancient COBOL systems don't seem to have realized the world has moved on, or if they do a fossilized management won't let them.
- Lack of availability. Unless you are actually being paid to work on one of these monsters you will not get access to one. There may even be one where you work but if your immediate job description does not include working on it you will not get a login. Much has been said in other postings about the "herecules" emulation software and it is indeed excellent but its very much for experts only, it runs an ancient version of the operating system, it lacks most of the standard components such as CICS,COBOL and DB2 which form the framework of most running mainframe applications.