Hypervisors generally allow creation of virtual devices (sound, USB, network), which will work in most cases. However, if you need more control over the device or more options than the stock virtual device gives, you are going to find yourself stuck. To get around this, PCI passthrough is used to pass a raw device (such as a sound card, RAID card, video card, etc) directly into a virtual machine. This gives unfettered access and to the virtual machine, it is treated as if the hardware were directly connected. In the guide below, I explain how to pass through PCI and USB devices to Xen Cloud virtual machines.