5 Virtual storage 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 where the virtual CD/DVD drive will be attached to one of the four ports of this controller. • 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 system 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 con- nect up to 30 virtual hard disks to one machine instead of just three, as with the VirtualBox IDE controller (with the DVD drive already attached). Of these, the first four (numbered 0-3 in the graphical user interface) are operated in IDE compatibility mode by default. For this reason, starting with version 3.2 and depending on the selected guest operating system, VirtualBox uses SATA as the default for newly created virtual machines. One virtual SATA controller is created by default, and the default disk that is created with a new VM is attached to this controller. Warning: The entire SATA controller and the virtual disks attached to it (including those in IDE compatibility mode) will not be seen by operating systems that do not have device support for AHCI. In particular, there is no support for AHCI in Windows before Windows Vista, so Windows XP (even SP2) will not see such disks unless you install additional drivers. It is possible to switch from IDE to SATA after installation by installing the SATA drivers and changing the controller type in the VM settings dialog.a aVirtualBox recommends the Intel Matrix Storage drivers which can be downloaded from http:// downloadcenter.intel.com/Product_Filter.aspx?ProductID=2101. To add a SATA controller to a machine for which it has not been enabled by default (either because it was created by an earlier version of VirtualBox, or because SATA is not sup- ported by default by the selected guest operating system), go to the “Storage” page of the machine’s settings 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, and you can add virtual disks to it. To change the IDE compatibility mode settings for the SATA controller, please see chapter 8.17, VBoxManage storagectl, page 121. • SCSI is another established industry standard, standing for “Small Computer System In- terface”. SCSI was standardized as early as 1986 as a generic interface for data transfer between all kinds of devices, including storage devices. Today SCSI is still used for connect- ing hard disks and tape devices, but it has mostly been displaced in commodity hardware. It is still in common use in high-performance workstations and servers. Primarily for compatibility with other virtualization software, VirtualBox optionally sup- ports LSI Logic and BusLogic SCSI controllers, to each of which up to 15 virtual hard disks can be attached. 72