The VSC7177 is a Serial ATA and Serial Attached SCSI multiplexer/buffer that implements a 2:1 port selector function for 1.5 Gbps and 3.0 Gbps links. This function is used when dual hosts, such as I/O controllers, must access single-port disk drives in high availability storage subsystems where redundancy and load sharing are important. The outputs from the I/O controllers are multiplexed to a Serial ATA or Serial Attached SCSI drive. The output from the Serial ATA drive is buffered and replicated to the I/O controllers. When switching from one I/O controller to the other, a Serial ATA link must be re-initialized with out-of-band (OOB) signals, which are transferred through the VSC7177 transparently. The VSC7177 provides high output swings, pre-emphasis, and programmable receiver sensitivity that are needed to drive long backplanes and external cables. Port connectivity for the device can be configured using driving external I/O pins or through protocol-based port. See the block diagram on page 2.