The signaling equals to what is used in SATA. Source: Adaptec.
Here comes the neat thing: Serial Attached SCSI supports both SCSI and SATA, which enables SAS controllers to run either SAS or SATA devices (or both). However, SAS devices cannot be operated on SATA controllers because the Serial SCSI Protocol (SSP) is used. Like SATA, SAS follows the principle of point-to-point links to the drives (currently 300 MB/s), while there is the option to use SAS expanders for attaching more drives than SAS ports available. SAS hard drives are dual-ported, each featuring his unique SAS ID, which means that it is possible to use two physical data connections to provide redundant data paths to two different hops/hosts. Thanks to STP (SATA Tunneling Protocol), SAS controllers will still be able to talk to SATA drives that are attached to an expander.
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