VIRTUAL MACHINES

Generally your guest OS does not need to be modified in order to run in a VM. However it is probably not running as efficiently as it should. The VM will never be exactly like the real hardware, it does what it can to replicate expected functionalities and translate commands from the guest. It’s not unlike speaking through a translator. It would be much easier to carry a conversation if your interlocutor could speak your language - even a little bit.

Well, most virtualization packages have reached that same conclusion. They provide additional software (mostly drivers) that can be installed on specific guest OS. With VirtualBox they are called Guest Additions.

Once installed, you may notice significant improvement at every levels: Memory usage, Sound, 3D support, Time synchronization, Better video support.