To access virtual disks, SCSI, and CD/DVD-ROM devices, a virtual machine uses virtual controllers. You can add a controller or change the controller type. With SCSI controllers, you can select bus sharing for a virtual machine.

Virtual controllers appear to a virtual machine as different types of controllers, including BusLogic Parallel, LSI Logic Parallel, LSI Logic SAS, VMware Paravirtual SCSI, and SATA.

When you create a virtual machine, the default controller type depends on the guest operating system and device type and is optimized for best performance. For example, when you create virtual machines with Apple Mac OS X, the default controller type for both the hard disk and the CD/DVD drive is SATA. When you create virtual machines with Windows guests, a SCSI controller is the default for the hard disk and a SATA controller is the default for the CD/DVD drive.

Each virtual machine can have a maximum of eight controllers, including four SCSI controllers and four SATA controllers. The default controller is numbered as 0. When you create a virtual machine, the default hard disk is assigned to the default controller 0 at bus node (0:0).

When you add virtual controllers, they are numbered sequentially 1, 2, and 3. If you add a hard disk, SCSI, or CD/DVD-ROM device to a virtual machine after virtual machine creation, it is assigned to the first available virtual device node on the default controller, for example (0:1).

If you add a controller, you can reassign an existing or new hard disk or device to that controller. For example, you can assign the device to (1:z ), where 1 is controller 1 and z is a virtual device node from 0 to 15.

By default, the virtual controller is assigned to virtual device node (z:7), so that device node is unavailable for hard disks or other devices.