HDD Controllers

HDD (Hard Disk Drive) Controller is a piece of hardware that connects directly to the motherboard allowing you to add more hard drives to your system by connecting them via the HDD Controller. This can be for a number of reasons such as increasing the storage size, hard drive mirroring or for hot swapping where a drive can be removed without powering the system down. The controller features its own processor which allows you to bypass the motherboards own limitations on controlling hard drives. Some HDD Controllers allow the use of RAID (redundant array of independent disks). Updated

Tekspek An in-depth guide into tech: System Buses & Bandwidth RAID

SATA / SAS / eSATA - 6-12 Gb/s

These controller cards are entry-level models that use a 1x PCI-E slot in order to provide faster SATA performance that any standard storage connector can provide. The products in this category have two connections for small-scale RAID arrays, and some work in Macs as well as PCs.