How Do SATA Cables Work?
By Bert Markgraf
SATA cables connect hard drives and optical drives to computers. These cables let the drives exchange data with the computer through the motherboard. SATA cables can transmit data faster than the older EIDE ribbon cables, and new hard drives, in particular, need the higher data transmission speed because they are larger and read and write data faster. While SATA drives perform at higher speed, the data they transfer is exactly the same as for the older cables.
IBM introduced a new interface for its personal computers in 1986. The company called the new computers AT, for advanced technology, and the new interface, used for connecting hard drives, was the advanced technology attachment (ATA). IBM used a parallel cable with 40 pins, with the conductors formed into a ribbon. The interface transferred data two bytes at a time, with a switch indicating whether the transfer was toward the disk or from the disk. With higher data transfer speeds, the parallel configuration was too slow. The serial ATA (SATA) system transfers the same data in series through a smaller cable.
SATA Signal Cables
The signal cables for the SATA interface have seven conductors in a flat cable. The plugs have a small jog at one end to make sure the cable is connected the right way. Two of the conductors are for sending data and two are for receiving. Ground wires between each signal conductor reduce interference between the signals, and make up the balance of the seven conductors. The cables plug into the back of the drive and into connectors on the motherboard. When the computer reads from disk or writes data to storage, the signals go through the SATA signal cables.
SATA Power Cables
The power cables for the SATA interface are of similar construction as the signal cables, but have 15 conductors. They supply power to the hard or optical drive at the voltage levels of 3.3, 5 and 12 volts. Each voltage has three conductors assigned to it because the wires and connecting pins are too small to be able to handle the full current required by the drive. Three ground wires between each two voltage levels make up the balance of the 15 conductors. The SATA power cables connect the computer power supply to the drives.
IBM designed the ATA interface to connect internal hard drives to the motherboard of the computer. Modern computers often have external drives for backup or data storage. The eSATA interface uses eSATA cables to connect external drives based on the same technology.
Structurally, eSATA cables are similar to SATA signal cables, but have shielding to prevent interference and use a different, more square plug. The cables connect the external drive to a port at the rear of the computer, located on a card installed in one of the computer's expansion slots. The card transfers the signal to the motherboard. The external drives usually have their own power supply, and don't use SATA power cables.
Bert Markgraf is a freelance writer with a strong science and engineering background. He started writing technical papers while working as an engineer in the 1980s. More recently, after starting his own business in IT, he helped organize an online community for which he wrote and edited articles as managing editor, business and economics. He holds a Bachelor of Science degree from McGill University.