memory available to 64bit Fedora guest under 32bit XP host running virtualbox

I have successfully installed a 64 bit Fedora 11 guest os using VirtualBox on a host machine (AMD64) running 32 bit Windows XP .

At the moment the host machine has 2 Gb ram installed and I've allocated 1 Gb to the guest, which all works well.

The host machine can hold a maximum of 4 Gb r开发者_运维问答am, so I was wondering if it's worth buying an extra 2 Gb for it.

I know that 32 bit Windows XP can't use all of the 4 Gb, but can the guest os use any of the ram that the host os can't use?

No, you are limited what the host OS can see. If you open up task manager in the host OS, the guest OS's memory is mapped within there, so having memory that's mapped outside of the host OS is not possible.

That shouldn't discourage you from getting the extra ram, however. If you upgrade to 4 (or 3.5GB) then you'll still have about ~3.2GB of addressable memory to use, which is a substantial increase over 2GB especially if your memory usage is already near 2GB.