A hardware RAID controller is a dedicated device that manages multiple hard drives or solid-state drives to improve performance and data redundancy. It uses its own processor and memory to handle data storage tasks, allowing for faster data access and better reliability compared to software RAID solutions. These controllers can support various RAID levels, such as RAID 0, RAID 1, and RAID 5, each offering different balances of speed and data protection. By offloading the RAID processing from the main system, hardware RAID controllers enhance overall system performance and provide advanced features like battery-backed cache for data safety during power failures.