SATA replaces parallel ATA. SAS replaces SCSI. Of course, the story is a little more complex than that. But generally speaking, that's what we can expect. In fact, it's perfectly true from a command standpoint. While SATA command blocks now look like SCSI command sequences, SAS commands implement a superset of SCSI commands. And, SATA is a superset of parallel ATA commands. Most SAS controller boards will support SATA devices and even recognize the differences when the drives are first accessed. SATA connectors will plug into SAS connectors, but not vice versa, enabling users to migrate from SATA drives to SAS drives should the application warrant.
SAS and the enterprise. SAS drives most likely will wind up in high-end and enterprise RAID systems, where long life and high throughput are top requirements. Unfortunately, many embedded applications demand these requirements as well. Such needs will be less of an issue for SAS controller boards, but embedded SATA controllers will have to contend with them. These controllers aren't likely to include SAS support. Luckily, SATA drives are benefiting from improved reliability, as even high-end systems use RAID arrays comprising SATA drives. Designers of embedded systems requiring higher levels of reliability may want to investigate SATA RAID alternatives, since even software-based solutions employ minimal processor overhead on mid-level to high-end microprocessors.
SCSI Trade Association drives SAS. SAS is the brainchild of the SCSI Trade Association. It was a wise idea to utilize the same form factor and physical interface as SATA. SAS drive availability lags behind SATA for a variety of reasons. However, SAS will start making an impact late in the year as drives with better characteristics than standard SATA drives begin to emerge.