Hacker News Reader

Comment by intpx | Hacker News Reader

pardon my ignorance, but how is QEMU not virtualization? There have been MacOS builds of KVM/QEMU for a couple of years now and I distinctly remember seeing that it had either been added or was being added to the base OS (google-fu is failing me because of so many results about the reverse-- running MacOS under KVM/QEMU).

View on HN

QEMU can either be used for virtualization (i.e. running x86 Linux on your x86 Mac) or emulation (i.e. running PPC Mac on your x86 Mac).

QEMU is an emulator, not virtualization. It allows the user to run an OS designed for one type of CPU on a host system of a different type. i.e running Raspbian (ARM Linux) through QEMU on an X64 Linux Host running on an X64 machine.

Virtualization, by contrast, allows the user to run a guest OS designed for the same architecture as the physical hardware. i.e running x64 Linux guest on an X64 host that runs Windows as a host OS.

But to add to the complexity, many virtualization systems use QEMU as a support library to achieve stuff.

I'm not nearly smart enough on that stuff. I fear I will need to get deeply into it in order to setup tooling that will run on the new Macs for embedded development.

That's hardly the point. Many virtualization systems do indeed use QEMU for device emulation, but they don't use it to emulate the entire CPU functionality itself. A key point about virtualization is that most code run native while privileged instructions are trapped and handled by the hypervisor, allowing multiple guest OSes to coexist. This gives guest OSes the illusion that it's in sole control of the hardware.

QEMU can do both the complete emulation you describe and accelerated virtualization similar to that offered by VMWare.

Reply on news.ycombinator.com