IBM Mainframe that cost a quarter of a million dollars in its day

Okay, you can "Buy it now" for $500...

But I suppose you'd need an OS license from IBM to operate the thing?

Or does Linux boot bare metal on z/Systems?

(Initial Program Load, sorry. One does not simply "boot" an IBM mainframe.)

It'd be cool if they hadn't scratched it up.. Also, I'm not entirely sure it can be booted up without the laptops ?