Sun Microsystems VIRTUALBOX VERSION 3.1.0_BETA2 User Manual

Page 77

5 Virtual storage

machine. (By default, one of these four – the secondary master – is preconfigured
to be the machine’s virtual CD-ROM/DVD drive, but this can be changed.

)

So even if your guest operating system has no support for SCSI or SATA devices,
it should always be able to see the default IDE controller that is enabled by
default.

You can also select which exact type of IDE controller hardware VirtualBox
should present to the virtual machine (PIIX3, PIIX4 or ICH6). This makes no
difference in terms of performance, but if you import a virtual machine from
another virtualization product, the operating system in that machine may expect
a particular controller and crash if it isn’t found.

After you have created a new virtual machine with the “New Virtual Machine”
wizard of the graphical user interface, you will typically see one IDE controller
in the machine’s “Storage” settings. Of the four slots of this controller, one will
be used by the hard disk that you probably created when you set up the VM, and
another one will be the machine’s virtual CD-ROM/DVD drive.

•

Serial ATA (SATA) is a newer standard introduced in 2003. Compared to IDE,
it supports both much higher speeds and more devices per hard disk controller.
Also, with physical hardware, devices can be added and removed while the sys-
tem is running. The standard interface for SATA controllers is called Advanced
Host Controller Interface (AHCI).

For compatibility reasons, AHCI controllers by default operate the disks attached
to it in a so-called “IDE compatibility mode”, unless SATA support is explicitly
requested. “IDE compatibility mode” only means that the drives can be seen and
operated by the computer’s BIOS. Still, disks assigned to those slots will operate
in full-speed AHCI mode once the guest operating system has loaded its AHCI
device driver.

Like a real SATA controller, VirtualBox’s virtual SATA controller operates faster
and also consumes less CPU resources than the virtual IDE controller. Also, this
allows you to connect up to 30 virtual hard disks to one machine instead of just
three, as with IDE. Of these, the first four (numbered 0-3 in the graphical user
interface) are operated in IDE compatibility mode by default.

To enable the SATA controller, on the “Storage” page of a virtual machine’s set-
tings dialog, click on the “Add Controller” button under the “Storage Tree” box
and then select “Add SATA Controller”. After this, the additional controller will
appear as a separate PCI device in the virtual machine.

The assignment of the machine’s CD-ROM/DVD drive to the secondary master was fixed before VirtualBox

3.1; it is now changeable, and the drive can be at other slots of the IDE controller or at other storage
controller such as the SATA controller, and there can be more than one such drive.