Complex sentence: A Serial ATA port multiplier is a unidirectional splitting device it allows one equipped port to connect to 15 disks, however the bandwidth available is limited to the 3 Gbit/s of the link to the controller.
Split into simpler sentences: A Serial ATA port multiplier is a unidirectional splitting device. While it allows one equipped port to connect to 15 disks, the bandwidth available is limited to the 3 Gbit/s of the link to the controller.