How SAS interface and SATA interface technology are compatible

The interface technology of SAS is backward compatible with SATA. 

Specifically, the compatibility of the two is mainly reflected in the compatibility of the physical layer and the protocol layer.

1. At the physical layer, the SAS interface is fully compatible with the SATA interface. SATA hard drives can be directly used in the SAS environment. In terms of interface standards, SATA is a sub-standard of SAS, so the SAS controller can directly control SATA hard drives. 

However, SAS cannot be used directly in the SATA environment, because the SATA controller cannot control the SAS hard disk.

2. At the protocol layer, SAS consists of 3 types of protocols, and the corresponding protocols are used for data transmission according to the different devices connected. Among them, Serial SCSI Protocol (SSP) is used to transmit SCSI commands; SCSI Management Protocol (SMP) is used to maintain and manage connected devices; SATA Channel Protocol (STP) is used to transmit data between SAS and SATA.

Therefore, with the cooperation of these three protocols, SAS can be seamlessly combined with SATA and some SCSI devices.