Mainframe OS vs NT

Is your question in relation to UNIX and COBAL, or more modern systems?

In the case of COBAL, it is still in use because organizations don't want to go through the change process on a system that works for them.

It has as much to do with entrenched technology as anything else.

Mainframe OSes are still popular because of two reasons:

1) Applications that are geared toward UNIX and a mainframe environment tend to run a lot faster and more relaibly on UNIX based systems.

2) Unix has been around a whole lot longer andnothing beats security on Unix.

Talking about OS/390, OS/400 and high-scale Unix, there are some other functions which are more difficult to get (though not completely impossible) in Windows:
* Fault-tolerance (which links to scalability but is different)
* Integrated DBMS functionality
* Security in EVERY application/object, on a consistent level using the same generic shell - e.g. RACF on OS/390
* Job scheduling, a lot more flexible and machine-independent than Windows's AT which runs on a per-processor basis
* Virtualmachine, i.e. multiple copies of the OS in one physical machine. A crash (if at all...) can never bring the whole machine down.
* Output management, also with tens of printers and >100 types of papersettings and document types.

Hope this helps,

- The Netherlands