Serial ATA Explained

What is Serial ATA (Advanced Technology Attachment)?

Serial ATA as the name suggests is a serial interface, which has been specifically designed to “eventually” replace the older parallel ATA disk interface. A number of the industry’s leading vendors have formed the Serial ATA Working Group to jointly develop the SATA interface. The Serial ATA 1.0 specification was first released in August 2001.

ATA is currently the standard interface for IDE hard drives and can be found in almost all consumer PCs, as well as many high end professional PCs. The current hard disk interface uses a 16-bit wide data bus to communicate. To do so involves using a wide 40-pin ribbon cable, (figure 1) the Serial ATA specification specifies a thin, point-to-point connection, (figure 2) which allows for easy cable routing, it also avoids master/slave combinations and improves airflow due to it’s small cable design profile.

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Serial ATA boasts data transfer speeds of up to 1.5Gbits/sec (150MByte/sec) and is expected to rise to 3Gbits/sec (300MByte/sec) in the near future. Rumours of speeds of up to 6Gbits/sec (600MByte/sec) are also in the news! Many motherboard manufacturers have been quick to introduce this new technology, and are now incorporating the new interface as standard on the latest motherboards.

Serial ATA currently supports legacy drivers for Parallel ATA technology and OEMs will be able to deploy the new technology using existing parallel ATA drivers. It’s also expected that some vendors will be providing bridges for Parallel-to-serial conversion. For those wishing to take advantage of the added benefits of Serial ATA then a range of add-in controller/raid cards (figure 3) and IDE to Serial ATA adaptors (figure 4) are currently available.

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How does Serial ATA work?

As with all computer technologies the need for speed has become paramount. The Serial ATA interface is no exception to this with speeds of up to 3Gbits/sec and greater being boasted. To achieve this increase in speed the interface has undergone a complete re-design and the once familiar 40 Way (80 wire) ribbon cable has completely disappeared.

To overcome a number of problems, and to achieve this high transfer rate, the Serial ATA interface was defined. The new interface employs a high-speed “differential pair” signalling technique, the data being transmitted over two separate pairs, and a separate power connector (figure 5) supplies the power for the device.

Put simply, to ensure compatibility with existing software drivers the existing ATA data format was retained and the devices output “serialised” and the input to the motherboard “de-serialised”. Serial ATA is intended to be a “drop-in” solution, in that it is compatible with today’s software, which will run on the new architecture without modification.

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