SATA | SAS | SCSI | PATA

SATA - Serial Advanced Technology Attachment

SAS - Serial Attached SCSI

SCSI - Small Computer System Interface

PATA - Parallel Advanced Technology Attachment

SATA is half Duplex where SAS is full duplex. Meaning SAS can transfer at the full speed of the link in both directions at once. Though SCSI commands that can take advantage of this feature are rare.

A telephone is a good example of full duplex. i.e. one can talk and listen at the same time. A walkie talkie is half duplex in that communication can go in both directions but not simultaneously.