Legacy system

The term Legacy system is widely used in almost any software engineering paper. It could be a lot of things, like a Mainframe, Old system in CLIPPER (do you remember that), C, Fortran, Win32, so on.
When we talk about SOA, MDA, Mule, connector architecture, etc there is always a reference to the advantage of connecting to the legacy.
Although many says about it few have a way to test it or even he is interested in testing it. But let's face, it is important to have an environment - mainly for architecture concept tests.
Among all these legacy systems the most complicated on is to have a Mainframe environment running, most of the time we just create a mock for it. But have you never desired to put some kind of system up and running? Or you have never been interested in know how the big-blue works?
Well if it is your desire as it is mine, take a look on the following link:

• The Hercules System/370, ESA/390, and z/Architecture Emulator
  

The Hercules is only the emulator, it is necessary to install the OS, Subsystem, Compilers, running system, RACF, VSAM, ISAM, etc. Looks complicated? Yes it is. But try to read this document for a brief introduction, please it is a old work from university

• zOs (portuguese).
  

I am not a specialist, but I know more or less how it works, if you are interested I can give you some tips.