Was a bit confused if mainframe simulator and emulator are two different entities, where the first one refers to and Windows based IDE which connects to mainframe. And the later would actually simulate the mainframe system on your desktop which would not need to be connected to mainframe server.
mainframe emulator ...
a PC software that emulates the facilties of a mainframe
hercules is an example ,
...a mainframe operating system is needed
What You are referring most probably is a 3270 Terminal emulator,
a PC program that emulates the feature of a 3270 to connect to a mainframe
for windows ( charge )
... IBM Personal Communication
... Vista 3270