Virtualization

VirtualBox Classic BIOS

Use F12 to call up the boot menu.
When booting from a CD-ROM and choosing "Boot local disk", VirtualBox hangs. This seems to be a problem exclusive to the VirtualBox implementation of Classic BIOS (does not occur on VMware platforms, or when using VBox EFI).
The VBE implementation offers modes from 320×200 to 1600×1200 in the default set (and some more via private INT 10h function 5642h, from 640×480 to 2560×1920, but this is not used by GRUB).
Default firmware resolution is 640×480.
If GRUB is set to use GRUB_GFXMODE=auto (cf. /etc/default/grub), which makes it simply retain that resolution. (This in contrast to e.g. choosing the maximum available resolution.)
A manual list of resolutions always inconveniences at least one concrete system, so we will leave the Grommunio installation media and default system settings at auto. You can change the resolution in existing systems to a suitable size.