The 12Gb/s SAS is designed for backward compatibility with 6Gb/s and 3Gb/s SAS/SATA hard drives. The 12Gb/s SAS interface supports both 12Gb/s SAS disk drives for data-intensive applications and 6Gb/s SATA drives for low-cost bulk storage of reference data. The ARC-1216-4i/4x and ARC-1226-8i/8x RAID controllers only support directly attach to 4/8 SAS/SATA drives without supporting the expand function. The ARC-12x6 series default support 1GB on-board DDR3-1600 SDRAM memory.