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I just installed a GCOS 8 system on a hardware emulator which is hosted on a RHEL 6 Linux system hosted on a KVM virtual machine on an Intel based hardware platform designed and built by Bull, a French company.

That's cool, what's it like? Is it a command line O/S, or does it have a GUI?
Is it Unix-like?

GCOS 8 is a mainframe system. Vintage mainframes are used by governments and the financial sector. The system is inherently command line, but its service processor is a GUI based system running on Windows 7.

Mainframes run programs in “batches”. The programs are usually written in COBOL and post-process the databases both for reporting, billing, restocking, and database management purposes. These batches of programs are usually run at night when the online needs of the system are greatly reduced. Hundreds, or even thousands, of batch programs can run every night.

During the day, transaction processing is king. Transaction processing terminals could be screens at a teller station or specialized programs to interact with a bank ATM. It would not be unusual to support 3,500 logged in terminals in a single system. Note, the system running these 3,500 terminals had only 4 CPUs and only a few gigabytes of system memory. During the 1980’s, these CPUs had a “clock speed” at least 1000 times slower than the speed of the processor on your phone.

The last leg of the three-legged stool is “time sharing”. That is to support people writing and submitting the programs for the batch and transaction processing systems. It is the closest thing to logging into a linux/unix system. 100 to 400 logged in users was typical. Today, staffs are usually smaller.