3 Configuring virtual machines 2. You must enable hardware virtualization for the particular VM for which you want 64-bit support software virtualization is not supported for 64-bit VMs. 3. If you want to use 64-bit guest support on a 32-bit host operating system, you must also select a 64-bit operating system for the particular VM. Since supporting 64 bits on 32- bit hosts incurs additional overhead, VirtualBox only enables this support upon explicit request. On 64-bit hosts (which typically come with hardware virtualization support), 64-bit guest operating systems are always supported regardless of settings, so you can simply install a 64-bit operating system in the guest. Warning: On any host, you should enable the I/O APIC for virtual machines that you intend to use in 64-bit mode. This is especially true for 64-bit Windows VMs. See chapter 3.3.2, “Advanced” tab, page 42. In addition, for 64-bit Windows guests, you should make sure that the VM uses the Intel networking device, since there is no 64-bit driver support for the AMD PCNet card see chapter 6.1, Virtual networking hardware, page 83. If you use the “Create VM” wizard of the VirtualBox graphical user interface (see chapter 1.7, Creating your first virtual machine, page 16), VirtualBox will automatically use the correct settings for each selected 64-bit operating system type. 3.2 Emulated hardware VirtualBox virtualizes nearly all hardware of the host. Depending on a VM’s configuration, the guest will see the following virtual hardware: • Input devices. By default, VirtualBox emulates a standard PS/2 keyboard and mouse. These devices are supported by almost all past and present operating systems. In addition, VirtualBox can provide virtual USB input devices to avoid having to capture mouse and keyboard, as described in chapter 1.8.2, Capturing and releasing keyboard and mouse, page 19. • Graphics. The VirtualBox graphics device (sometimes referred to as VGA device) is, unlike nearly all other emulated devices, not based on any physical counterpart. It is a simple, synthetic device which provides compatibility with standard VGA and several extended registers used by the VESA BIOS Extensions (VBE). • Storage. VirtualBox currently emulates the standard ATA interface found on Intel PIIX3/PIIX4 chips, the SATA (AHCI) interface, and two SCSI adapters (LSI Logic and Bus- Logic) see chapter 5.1, Hard disk controllers: IDE, SATA (AHCI), SCSI, SAS, page 71 for details. Whereas providing one of these would be enough for VirtualBox by itself, this mul- titude of storage adapters is required for compatibility with other hypervisors. Windows is particularly picky about its boot devices, and migrating VMs between hypervisors is very difficult or impossible if the storage controllers are different. • Networking. See chapter 6.1, Virtual networking hardware, page 83. • USB. VirtualBox emulates two USB host controllers, EHCI and OHCI. There is a need for two host controllers because OHCI only handles USB low- and full-speed devices (both USB 1.x and 2.0), while EHCI only handles high-speed devices (USB 2.0 only). The emulated USB controllers do not communicate directly with devices on the host but rather with a virtual USB layer which abstracts the USB protocol and allows the use of remote USB devices. 41