Quick Technology Overview

Most desktop storage systems today use a parallel bus interface referred to as Ultra ATA/100. The Parallel ATA interface has been in use on desktop systems as the mainstream internal storage interconnect since the 1980s (over 15 years!). Today’s PCs demand higher speeds, more robust data integrity and flexibility for innovative smaller designs. Physically and electrically, the current parallel bus has run into limitations that will prevent this bus from providing higher speeds of data transfers. The move to a new technology is inevitable in the eyes of industry leaders such as Intel, Dell, Seagate, Maxtor and APT.

These same leaders formed the Serial ATA Working Group and are dedicated to bringing this new technology to the forefront of today’s PCs. Serial ATA is designed to overcome the limitations of Parallel ATA while providing scalability for years to come. Setting the goal to be compatible and at cost parity with current Parallel ATA drives when in volume, the Serial ATA Working Group is promoting the adoption of Serial ATA in all systems where ATA drives are being used today.

It's Easier

Serial ATA eliminates the need for master/slave jumpers by creating a single drive connection from the drive to the host or motherboard. This is called point-to-point connection. Another feature is the replacement of the flat gray cable that blocks airflow and limits the drive mounting locations. Replacing the gray cable led to improving the connectors from a 40-pin and socket connection to a simple snap-in ¼-inch blade and beam connection. These improvements may streamline the system build time by minutes per system, saving customers time and money.

It's Faster

Serial ATA can transfer up to 300 Mbytes/sec because the interface does not have the complicated timing restraints of Parallel ATA. For instance, Parallel ATA must send 16 signals all at once down the cable. If the signals arrive improperly skewed or timed, incorrect data will be received. So the pace that bits are sent must be slow enough to allow setup and settling time. Serial ATA only sends 1 bit at a time, therefore that bit can be sent much faster. This is similar to playing catch with a ball. Catching one ball at a time is easier than trying to catch 16 balls all at once. Clearly, dealing with one ball (bit of data) is easier to ensure integrity (no balls dropped) and greatly increases the speed at which you can throw the ball (25 mile per hour pitch with 16 balls vs. 1500 mile per hour pitch with one ball). The only way to dramatically increase the speed of Parallel ATA is to add more bits, but then you would have to add more wires to the wide gray cable, more pins to the hard drive and you would need more power to drive more signals through the wires. This is inefficient and expensive.

It’s Protective

Improved data reliability is another area where Serial ATA makes a significant impact. Serial ATA’s Cyclic Redundancy Checking (CRC) gives improved data reliability from the start of the data transfer to the end, from command to status. This differs from Parallel ATA by wrapping CRC around the command and status, as well as the data. This ensures that data will arrive at the designated destination accurately.

It's the Future of Economical Storage

Low-cost storage or personal computing storage is >85 percent of the disc drives sold today. These drives satisfy a multitude of cost-sensitive application storage requirements from personal computers and consumer electronic devices to entry-level servers. If the industry tried to upgrade Parallel ATA without moving to serial technology, the price of personal storage drives would most likely increase. Cables and connectors would have to add more robust material, wires or other components to handle the increase in noise due to higher transfer speeds. And the controller chips on the drive PCBA would require similar or more power consumption with any added electronics to control signaling. Serial ATA gives manufacturers a path to continued capacity and performance growth while remaining an economical choice for low to medium transactional workloads.

There are New Opportunities

Seagate customers who choose to integrate Serial ATA give their solutions a unique and economical selling differentiator with all the benefits you’ve been reading about in this paper. In addition, there are new opportunities that are quickly emerging because Serial ATA provides easy integration technology that was missing from Parallel ATA. These new markets include nearline storage with disc drives and virtual tape backup systems using drives as the answer to quick retrieval.

Seagate Is Native Serial ATA and Others Are Bridged

The Seagate Serial ATA solution is a native one! Seagate chose to integrate Serial ATA into our core controller logic. The Seagate native architecture allows intelligent data handling such as command queuing, hot plugging and enclosure services. The other solution, bridged, is merely a translator from parallel signal to serial. This type of solution will have higher command overhead and can affect performance. In addition, bridged solutions cannot easily take advantage of Serial ATA extensions such as native command queuing, hot plugging, and staggered spin up (there are more). Bridged solutions will require new ASIC designs in order to be compatible with the Serial ATA II specification or to enable any enhancements to Serial ATA 1.0 specification.

And The Bottom Line Is…

Integrating Serial ATA today gives Seagate customers a competitive edge by offering state-of-the-art drive interface technology, improved system performance and reliability, and technology that inspires new opportunities. Use Serial ATA to build your business and expand into new markets.