If you’ve ever used DOS or some other command line OS in VirtualBox, you’ve probably noticed that resizing the window does absolutely nothing to the size of the VM itself. When you switch your VM to fullscreen mode, it looks something like this:
Look at that. That’s horrible. The VM is tiny and it’s surrounded by huge black margins on all sides. How do we fix that?
Well, it turns out there actually is a way, though you can’t do it from any of the VirtualBox menus. You have to go to the VirtualBox VM process and use its menus.
There, doesn’t that look better? Now you don’t have those huge black margins on all four sides, and your fullscreen VM looks more convincing, meaning it looks more like it would if you had it installed to real hardware.