Each major revision of the Serial ATA interface specification has doubled the maximum data transfer rate. The latest SATA Revision 3.0 allows for data transfer speeds of up to 6 Gbps.
While the cables for all three revisions appear to be similar and will physically fit into the connectors on all SATA drives and controllers, the higher data transfer rate of SATA 6 Gbps requires higher quality materials and closer tolerances than the previous two revisions required.
SATA 6 Gbps cables are certified to provide maximum speeds from your SATA system, up to 6 Gbps when used with equivalent devices and controllers.
Note that SATA 6 Gbps cables are backward compatible and can be used with SATA 3 Gbps and SATA 1.5 Gbps devices. However, the data transfer of the SATA subsystem will be limited to that of the slowest device. So, for example, if a SATA 6 Gbps cable is connected to a SATA 3 Gbps drive and a SATA 1.5 Gbps controller, the drive will be limited to a transfer rate of 1.5 Gbps.