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Electronic Design

An Interview: Serial ATA Drives Will Soon Replace Their Parallel Brethren

Question: How quickly do you see Serial ATA replacing parallel ATA hard drives?

Answer: Dell is launching high-end Serial ATA hard drives this month in desktop products. We expect to begin shipping mainstream Serial ATA hard drives later this year, with the vast majority of desktop drives transitioned by early 2004. Once the transition from parallel to Serial ATA gains momentum, I expect it will occur rather quickly.

Q: Will Serial ATA drive speed need to rise quickly to stave off parallel ATA?

A: The most significant enhancements to ATA drives are happening today in Serial ATA: higher data transfer rates and added features like command queuing. Parallel ATA has really topped out at 133 Mbytes/s. Serial ATA, on the other hand, begins at 1.5Gbits/s (equivalent to 150 Mbytes/s) with spec work going on now to define a 3.0-Gbit/s transfer rate.

Q: What are the key benefits to using Serial ATA on the desktop?

A: There are several benefits. The higher data-transfer rates as just described are more reliable due to the application of CRC error correction to both data and commands. (The latest parallel ATA spec includes CRC for data only.) The longer, thinner cables enable more flexible system layouts, easier assembly and installation, and better airflow inside the chassis. The width and bulk of the older parallel ATA cables can create hot spots inside the chassis due to restricted airflow, which will only become more problematic with increasing power requirements of processors and graphics subsystems. Serial ATA also uses low signaling voltages and fewer pins, both of which will be required to take advantage of ever smaller silicon geometries.

Q: What are Dell's plans regarding Serial Attached SCSI?

A: As Serial ATA is to parallel ATA, Serial Attached SCSI is the evolutionary follow-on to SCSI, using higher-speed, point-to-point serial interconnects. We expect to take advantage of Serial Attached SCSI when that technology is ready, with Serial Attached SCSI and Serial ATA playing complementary roles.

Q: Do you expect to eliminate floppy and parallel ATA interfaces on some motherboards in favor of Serial ATA interfaces?

A: The first step in this transition is to add Serial ATA ports, which is where we are today. Later, as the transition progresses, the number of Serial ATA ports will increase while the number of parallel ATA ports will decrease, with Serial ATA eventually displacing parallel ATA altogether. The removal of the floppy interface is a separate matter, because the floppy is not available on, or transitioning to, either parallel or Serial ATA. The removal of the floppy interface will be tied to our customers' demand (or lack of demand) for floppy drives. We have begun to offer some floppy-optional systems as well as floppy alternatives to our customers to enable them to make the best choice for their situation.

Q: How should data center managers plan for the use of Serial ATA drives?

A: They should plan to use Serial ATA drives wherever parallel ATA drives are used today mainly in applications requiring optimal cost/capacity. They can also realize added benefits over parallel ATA in those applications, such as hot plug, higher data-transfer rates, and increased data/command transfer reliability.

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