Mikhailtech have an article discussing server technology and concept - in layman terms

SATA and SAS are both relatively new to the game. SATA is a technology most readers will be very familiar with, so we won't dwell on it. SAS however is a newer technology made for servers. It is backwards compatible with SATA (sounds odd for anything to be backwards compatible with something so new, doesn't it?) and uses the same cabling. The big difference is in the way data is transferred; SAS uses the same SCSI commands as parallel SCSI, except in a serial format. These point to point connections allow for faster data transfers (up to 6 GBps) and do not suffer from having multiple devices on the same cable in the same way that parallel SCSI does. Because of different signaling strengths, SAS can have a cable up to 8m, versus standard SATA which is limited to 1m.

Introduction To Server Technology & Concepts Article