OS/380: a family of free 31-bit mainframe OSes incl. MVS/380, VM/380 and VSE/38

The whole "imaginary mainframe architecture" thing always seemed ugly to me.

I wonder how hard it would be to hack MVS 3.8J to run on 370/XA? I know the big problem is the incompatible IO channels. Too much work, unlikely to happen.

Or an XA mode hypervisor that supports 370 mode guests? Again, too much work, unlikely to happen.

So I see why people went this way in practice, even if it seems kind of ugly from one viewpoint.

I know one reason was that so GCCMVS could recompile itself. I wonder if you could hack GCC to use less memory. Break the compilation up into phases with separate executables and use disk for intermediate storage. Store large memory structures on disk and swap them in/out of memory as needed. Would make things even slower, but would be closer to how compilers used to work, back in the days of memory-constraint. I suppose again, too much work, not happening.

Posted because some people were interested in:

https://news.ycombinator.com/item?id=35300259