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Comment by msla | Hacker News Reader

This is because VM means two different things and has for a long time:

IBM's VM was and is a hypervisor. It dates to the mid 1960s, in the form of CP-40, and it didn't run opcodes in software, but in hardware.

https://en.wikipedia.org/wiki/IBM_CP-40

p-code machines, which interpret bytecode, date back almost as far, such as the O-code machine for BCPL.

https://en.wikipedia.org/wiki/BCPL

Getting people to distinguish between these concepts is probably a lost cause.

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Looking at the IBM's tech from the sixties is somehow weirdly depressing: it's unbelievable how much of the architectural stuff they've invented already by the 1970.

Not depressing, but inspiring. So many great architectural ideas can be made accessible to millions of consumers, not limited to a few thousand megacorps.

I remember seeing VMware for the first time and thinking that the PC world had finally entered the 1970s.

Close, but not quite -- you can't nest the VMs the way you can on "big iron"

I know Nested Virtualisation is a thing on both KVM and hyper-v, what is different about what you could do on "big iron"

A VM nest in "big iron" isn't a special case. It's a context push with comparatively exhaustively defined costs, side effects, and implications.

IMO, it’s only a special case for commercial support reasons. Almost every engineer, QE, consultant, solution architect I know runs or has run nested virtualization for one reason or another.

And licensing - DB2 and Oracle.

In the early days of virtualization on PCs (things like OS/2's dos box) the VM was 100% a weird special case VM that wasn't even running the same mode (virtual 8086 vs 286 / 386 mode), and that second-class functionality continued through the earlier iterations of "modern" systems (vmware / kvm / xen).

"PC" virtualization's getting closer to big iron virtualization, but likely will never quite get there.

Also -- I was running virtual machines on a 5150 PC when it was a big fast machine -- the UCSD P System ran a p-code virtual machine to run p-code binaries which would run equally well on an apple 2. In theory.

So what might you say hasn't been brought in from the 80s yet?

> Getting people to distinguish between these concepts is probably a lost cause.

I think people here of all places should distinguish between these concepts.

There are big performance and security implications of the two approaches.

I don't think anyone has ever been confused because of the conflation of these two terms. The context typically makes it very clear.

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