Sun Microsystems VIRTUALBOX VERSION 3.1.0_BETA2 - Manual (Page 76)

5 Virtual storage
As the virtual machine will most probably expect to see a hard disk built into its virtual
computer, VirtualBox must be able to present “real” storage to the guest as a virtual
hard disk. There are presently three methods in which to achieve this:
1. Most commonly, VirtualBox will use large image files on a real hard disk and
present them to a guest as a virtual hard disk. This is described in chapter 5.2 ,
Disk image files (VDI, VMDK, VHD, HDD) , page 79 .
2. Alternatively, if you have iSCSI storage servers, you can attach such a server to
VirtualBox as well; this is described in chapter 5.8 , iSCSI servers , page 86 .
3. Finally, as an experimental feature, you can allow a virtual machine to access
one of your host disks directly; this advanced feature is described in chapter
9.11 , Using a raw host hard disk from a guest , page 145 .
Each such virtual storage device (image file, iSCSI target or physical hard disk) will
need to be connected to the virtual hard disk controller that VirtualBox presents to a
virtual machine. This is explained in the next section.
5.1 Hard disk controllers: IDE, SATA (AHCI), SCSI
In a real PC, hard disks and CD-ROM/DVD drives are connected to a device called
hard disk controller which drives hard disk operation and data transfers. VirtualBox
can emulate the three most common types of hard disk controllers typically found in
today’s PCs: IDE, SATA (AHCI) and SCSI.
1
• IDE (ATA) controllers have been in use since the 1980s. Initially, this type of
interface worked only with hard disks, but was later extended to also support
CD-ROM drives and other types of removable media. In physical PCs, this stan-
dard uses flat ribbon parallel cables with 40 or 80 wires. Each such cable can
connect two devices to a controller, which have traditionally been called “master”
and “slave”. Typical hard disk controllers have two connectors for such cables;
as a result, most PCs support up to four devices.
In VirtualBox, each virtual machine has one IDE controller enabled by default,
which gives you up to four virtual storage devices that you can attach to the
1 SATA support was added with VirtualBox 1.6; experimental SCSI support was added with 2.1 and fully
implemented with 2.2. Generally, storage attachments were made much more flexible with VirtualBox
3.1; see below.
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