Answer:
If I am working on a mainframe I shall choose z/OS.This Operating System are specially design for Mainframe by IBM. It is widely used mainframe operating system, is designed to offer a stable, secure and continuously available environment for application running on the mainframe. as control program, z/Virtual Machine (z/VM) is a hyper-visor because it runs other operating system in the Virtual machines it creates.
In Linux, Unix operating system z/OS component must be included.
z/Os is a 64-bit operating system for IBM mainframes. It derives from and is the successor to OS/390.Which in turn followed string of MVS versions.