On Wed, 8 Jan 1997, John G. Alvord wrote:
> On Tue, 07 Jan 97 22:00:17 +1000, bofh@snoopy.virtual.net.au wrote:
>
>
> > Running Linux in Linux in Linux would be a great thing! I've been reading
> >reports about how IBM's older mainframes worked and specifically about the
> >architecture of VM/DOS. Apparently they had a virtual machine which the OS ran
> >in, the VM provided file access and linear memory to the OS.
> I did a lot of work on that system, called VM. There was a control
> program (CP) which ran virtual machines. It was all written in S/370
> assembler and was about 300K lines of code (VM and the user interface
> called CMS which had a file system, an exec language, and little else).
> Of course that excludes compilers, etc.
>
> Most of the work was a detailed simulation of memory and I/O. S/370 I/O
> is complex, involving channel programs (you don't want to know). It also
> simulated privileged instructions. The result was sufficient to run VM
> under VM, which was a marvelous development environment. Imagine single
> stepping, breakpointing, etc at the kernel level.
>
> A big project to duplicate. Incidently, VM still exists and is being
> enhanced even today.
>
> john alvord
>