It seems that, at least when running on a Windows host, the virtual box only has some predefined screen resolutions: 1600x1200, 1280x1024, 1152x864, 1024x768 and 800x600.
These predefined resolutions can be extended with a custom video mode . First, the virtual machine must be stopped. Then (within cmd.exe), VBoxManage.exe can be executed:
"c:\Program Files\Oracle\VBoxManage.exe" setextradata "VIRTUAL BOX NAME HERE" CustomVideoMode 1600x900x32
Arch Linux
Apparently, under Arch Linux, VirtualBox is loaded through/via/by the vboxdrvkernel module which must be loaded before any virtual machine can run.
The user who wants to use the VirtualBox must be member of the vboxusers group:
gpasswd -a $USER vboxusers
Apparently, the executable to start the VirtualBox, virtualbox, must be installed separately:
sudo pacman -S virtualbox
TODO: Apparently, it cannot hurt to also install virtualbox-guest-iso.
TODO: does it also need sudo pacman -S virtualbox-host-modules-arch?
Windows / Hyper-V
As per some comments that I found in the vast depths of the Internet, VirtualBox cannot be run on Windows 10 if Hyper-V is active because Hyper-V does not release VT-x once it has acquired it.
Apparently though, VirtualBox and VMWare can coexist.
However, at least with VirtualBox version six, there using VirtualBox with Hyper-V is an experimental feature: Virtual Box will use Hyper-V if it detects it. Such a configuration is indicated by a CPU icon in the VM window status bar.
Apparently, the interaction with Hyper-V leads to performance degradation.
An advantage of VirtualBox over Hyper-V is that it is free and also runs on a Windows home edition.
Auto Capture Keyboard
When Auto Capture Keyboard is enabled, it causes the Virtual Machine to automatically capture the keyboard every time the VM window is activated and make it unavailable to other application running (for example Alt-Tab).
This feature can be enabled or disabled in the Virtual Machine Manager's Menu Preferences -> Input -> Keyboard -> Keyboard Settings.
A portable runtime library which abstracts file access, threading, and string manipulation. Whenever Oracle VM VirtualBox accesses host operating features, it does so through this library for cross-platform portability.
VMM
The Virtual Machine Monitor, which is the heart of the hypervisor.
EM
The Execution Manager controls execution of guest code.
TRPM
The Trap Manager intercepts and processes guest traps and exceptions.
HM
The Hardware Acceleration Manager provides support for VT-x and AMD-V.
GIM
The Guest Interface Manager provides support for various paravirtualization interfaces to the guest.
PDM
The Pluggable Device Manager is an abstract interface between the VMM and emulated devices which separates device implementations from VMM internals and makes it easy to add new emulated devices. Through PDM, third-party developers can add new virtual devices to Oracle VM VirtualBox without having to change Oracle VM VirtualBox itself.
PGM
The Page Manager is a component that controls guest paging.
TM
The Time Manager handles timers and all aspects of time inside guests.
CFGM
The Configuration Manager provides a tree structure which holds configuration settings for the VM and all emulated devices.
SSM
The Saved State Manager saves and loads virtual machine state.
VUSB
The Virtual USB layer which separates emulated USB controllers from the controllers on the host and from USB devices. This component also enables remote USB.
DBGF
The Debug Facility is a built-in VM debugger.
Misc
VirtualBox was originally created by innotek GmbH which was acquired by Sun Microsystems Inc. (2008) which in turn was acquired by Oracle (2010).
TODO
VboxSDS is the process (service) that monitors a guest's system resources (VBoxManage.exe metrics). This process/services ends shortly after all VMs and frontends have been closed.
PS C:\> (get-service VBoxSDS).displayName
VirtualBox system service