virtualbox.org

Hello.

When I boot a virtual box to a "cd" iso for Windows or Linux, how does the box know that it is booting to a cd and that a hard drive exists? I was thinking a virtualbox or vhd was just a virtualized hard drive but they seem to know that a virtual cdrom and a virtual hard drive exists.

The virtual hard drive and the virtual CD drive are created when you create the virtual machine. The virtual hard drive is a file on the host machine and the virtual hard drive is an emulated device. By the time you get to the stage of installing an OS they both exist.