A Serial ATA port multiplier is a unidirectional splitting device. While it allows one equipped port to connect up to 15 disks, the bandwidth available is limited to the bandwidth of the link to the controller, as of 2012 1.5, 3, or 6 Gbit/s. While the controller is aware that there are multiple drives connected, the service is transparent to the disks attached. Because they believe they are communicating directly with the controller, any drive that holds to the SATA standard can be connected to a port multiplier. There are two ways port multipliers can be driven.