Serial ATA uses 8B/10B encoding. This means that 10 bits are used to transfer 8 bits. The first standard of SATA used 1.5 GBit/second transfer speed (or 1.2 GBit/second usable data rate). This is only slightly faster than the last PATA standard (ATA/133). Later standards doubled this rate, at almost every revision. These values are transfer speeds, because of signalling, the usable speed is 25% lower. 