Serial ATA (SATA) and Parallel ATA (PATA) are two different (and incompatible) connection standards for hard drives, optical drives and other storage media.
PATA is also called IDE, EIDE, ATA-5, ATA-6 and UltraATA. It uses a 40 pin (desktop) or 44 pin (laptop) ribbon cable and connector. Desktop PATA drives typically also have a 4 pin Molex power connector. Laptop PATA interfaces incorporate the power into the 44 pin connector.
Serial ATA drives use a 4 pin data connector, and a 9 pin power connector. The cables are much smaller and more flexible than the PATA ribbon cables.
Serial ATA controllers and drives come in three different speed standards; SATA I 1.5 Gbps, SATA II 3.0 Gbps and SATA III 6.0 Gbps. The drives and controllers are backwards compatible, so the speeds can be interchanged, and will automatically run at the speed of the slower device. The distinction between 3.0 Gbps and 6.0 Gbps is lost on hard drives, because a rotating hard drive can’t match even the 3.0 Gbps bandwidth, but it can show performance increase on flash based SSD drives and high end RAID arrays of hard drives. For the highest speeds, both the drive and the motherboard SATA controller must support 6.0 Gbps operation.
Serial ATA uses one motherboard connector and one data cable per drive. An external version of SATA with more robust connector and cable design is called eSATA. There is an eSATA mode called Port Multiplier which allows up to four hard drive data signals to be carried one eSATA cable. This requires both the controller and the device to be Port Multiplier (PM) capable, and due to the bandwidth limitations of the single port, the data transfer is not as fast as four individual drives on four separate ports. SATA Background
PATA (EIDE) comes in three speeds IDE-33, IDE-66, IDE-100 (plus IDE-133 which was never an official standard but was a speed promoted by the drive company Maxtor).IDE-33 was used by optical drives long after hard drives had standardized on the faster 66 or 100 form. In general though, a PATA or EIDE drive will be compatible with any PATA or EIDE connection. One PATA motherboard connector typically supports two drives, a Master and a Slave. PATA ribbon cables usually have two drive connectors separated by a few inches. Background
SATA and PATA hard drives usually come in 2.5″ wide (laptop) and 3.5″ wide (desktop) formats, although there are some 1.8″ and smaller variants used in netbooks and audio players.