virtualbox.org

In my experiences with VMware, it always asks whether I will use a CD or an .iso file to install the OS from.
VirtualBox goes ahead and assumes that a CD will be the boot device, even for Linux.
Is there no way to use an .iso file for installation?

If the vm is stopped - in the settings of the vm, highlight the CD/DVD drive and click on the disk icon. You can select an iso or the host drive.

If the vm is runnng click on the Devices tab of its window.

You can "insert" an ISO file into the virtual CD drive.
No need to prompt, just load what you need.