What Is SATA?

In some ways, Serial ATA can actually be seen as taking a step back by old standards. The main difference between Serial and Parallel ATA is the way they transfer data. Parallel ATA uses 16 separate wires to send 16-bits of data simultaneously in a single clock cycle. Hence, it uses a wide flat cable.

Serial ATA, on the other hand, sends data one bit at a time with each bit taking a clock cycle. Because Serial ATA takes 16 times as many clock cycles to transfer data that Parallel ATA can do in one clock cycle, many would think that Serial ATA would be a lot slower than our current Parallel ATA standard. However, the main speed advantage of Serial ATA is design elegance. Instead of thinking in terms of increased clock cycles or making the bus wider to accommodate more bits, they made a communication standard that is both leaner and faster.

Parallel ATA cable vs. Serial ATA cable
Courtesy, Seagate

First off, there is a reduction in connector size, from 40 pins of Parallel ATA to just 7 pins. The consequently thinner cable eliminates electromagnetic interference that cause errors when reading from IDE drives. In addition, the differential pairs for the data transfer channels greatly reduces electrical interference. And of course, the cable length can now extend up to 1 meter long!

Next, SATA is a point-to-point connection. There are no masters or slaves but only direct connections from the SATA controller to SATA drives. This eliminates overhead from drive arbitration (whenever two hard drives are trying to transfer data on the same cable).

The signal voltage (oh yes) is now a lot lower, going from 5.0 volts to just 0.7 volts. The lower voltage has the benefit of lowering power consumption and thermal output. It will also reduce the size of SATA controllers.

Finally, SATA comes with a big improvement in error correction. Not only has the error correction on data transfers been improved upon, error correction on instructions coming into the hard drive has also been added! The result is faster and more reliable data coming back to SATA controller.