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
A simple disk array controller may be integrated with a host bus adapter (HBA) to form a single adapter to easily fit inside a computer. These additional add-in cards allow you to add more IDE or Serial ATA drives to your system to give you more storage capacity. Some of these cards also allow the use of RAID thus increasing the performance and data security.
These additional add-on cards enable to add more SATA/SAS/eSATA drives to your system to give more storage capacity according to the card type. Some of these cards also allow the use of RAID thus increasing the performance and data security.
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.
A simple disk array controller may be integrated with a host bus adapter (HBA) to form a single adapter to easily fit inside a computer. These cards allow the use of SCSI drives within a system that does not usually have SCSI ports. The RAID controllers allow the use of the various types of RAID when used with multiple hard-drives thus increasing the performance and data security.