Diffferent versions of the Serial ATA standard are compatible with each other. This means that older devices can be operated on a newer controller, but they will only support the features and speed of the standard for which they were built. Similarly, devices built for a newer standard can be operated on an older controller. In this case, the controller is the limiting factor, and some of the newer functions may not be supported. An SAS (Serial Attached SCSI) controller is compatible with SATA drives, but a SATA controller is not compatible with SAS drives.