[nsguy]

I've used a 3090 and some of the predecessors and VM/CMS. The "monitor" was called CP (control program) IIRC.

XEDIT was a great editor. There was also Rexx (and previously EXEC and EXEC/2) as the system's programming language that you could use to customize virtually every aspect of the editor and automated tasks. Rexx had integration with the editor and also integrated with the OS there were lots of these small integration points that let you do really powerful stuff. Applications like email were implemented on top of the basic OS and editor. A very unique and powerful architecture (mirrored to some degree in OS/2 later).

The ecosystem was incredible. The virtualization support in the CPU let you run a complete multi-user system with each user having a visualized CPU within one virtual CPU. I.e. it was "fully" virtualized. What's more incredible is that a lot of these pieces, like the OS, were all written in assembly. Super robust. Super clean. Amazing documentation for everything. As top notch engineering as it gets.

The full screen terminal (e.g. 327X) were part of the architecture, delegating a lot of the interaction to the terminal. Interesting enough you could poll the terminals for input which we've used for writing some games. A friend of mine wrote a library for doing that. There were also colour/graphics terminals like the 3279 and could be programmed e.g. with a library called GDDM.

EDIT: - https://en.wikipedia.org/wiki/VM_(operating_system)

Another interesting bit is that IBM shipped the full source code for everything (I think this was by default). They also had a shared bug reporting system (anyone remember what that was called?).

[PaulHoule]

Right. It was really common for sites in the 1970s to compile their own OS so they could set the configuration. This was how you told it which devices where attached on which ports.

[ngcc_hk]

"compile their own OS"??? I thought SYSGEN is necessary. At least in 1990s when I supported these machines as OS (and later DB2) supports.

I suspect it is in general necessary even to these days, but whether they will start with MVS 3.8 and gradually build up to whatever machine we are onto, I am not sure.

[ngcc_hk]

I do not know you can do that as I think the 3270 block mode always did that. Might be CICS can do that but I wonder ... I only support block mode.

It would be interesting whether yo can release to six pack VM for us to try. We use 370 C to do gaming currently, ... does it allow this interaction I wonder.