A SAS Expander is a device used in computer storage systems to increase the number of Serial Attached SCSI (SAS) devices that can be connected to a single SAS controller. It allows multiple drives to be connected through a single cable, enhancing the scalability of storage solutions. This is particularly useful in data centers where space and efficiency are critical. The SAS Expander works by managing the communication between the SAS controller and the connected drives, enabling them to share bandwidth effectively. It supports both SAS and SATA drives, making it versatile for various storage configurations.