[ubuntu-uk] Virtualbox Advice

Liam Proven lproven at gmail.com
Tue Mar 4 13:39:35 UTC 2014

On 4 March 2014 11:28, Matt Wheeler <m at funkyhat.org> wrote:
> Actually the way this works is using the proper hardware
> virtualisation capabilities of the CPU, so the performance will be the
> same as running on a 64bit host OS. It's not possible to run a 64bit
> guest on a host system without VT-x or AMD-V (even if the host OS is
> 64bit)

I would expect it to use hardware virtualisation, yes, and that works
fine on 32-bit host OSes. But surely a task on 32-bit host Windows or
Linux can't execute 64-bit code, because the CPU isn't in Long Mode?

And even with PAE, a 32-bit host OS has 4GiB of virtual address space,
typically split 2:2 or 1:3 between kernel and app space, so a single
32-bit app can't have more than 2GiB or possibly 3GiB of process
space. So your fancy 64-bit guest OS only gets 2GB or 3GB of
contiguous address space, surely? In which case, what's the point of
having a 64-bit guest?

Mac OS X is a bit different and 32-bit kernels *can* execute 64-bit
processes. AFAIAA Linux and Windows can't. I welcome correction,

Liam Proven * Profile: http://lproven.livejournal.com/profile
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