Host bus adapter
A host bus adapter ( HBA ) - also called a host adapter - is a hardware interface that connects a computer system to internal or external devices such as storage or network devices . It extends the capabilities of the computer to include hardware compatibility with a specific bus system . The HBA is in turn connected to an internal bus of the computer (e.g. the PCI bus) and thus enables data to be exchanged with devices or other computers across multiple bus systems.
A host bus adapter is available both as an optional extension ( plug-in card ) and soldered onto the main board .
Host bus adapters are often referred to in common parlance using the English word "controller" (eg " IDE controller"). But this is - even in English - not a correct name, since the connected devices nowadays all have their own controller and the host bus adapter does not fulfill this task. The name “controller” comes from a time when hard disks did not have their own controllers and the hard disk controllers were actually plugged into the motherboards of computers as plug- in cards (see e.g. ST506 interface , ATA / ATAPI: history ). Today, hard drive controllers are housed on the underside of hard drives on their circuit boards. The latter also contains the interface to the bus system.
The term is primarily used in connection with the bus systems SCSI , ATA (IDE), SATA and Fiber Channel . In principle, however, a network card is also an HBA.
Another type of HBA is the TCP Offload Engine (TOE). A TOE can be compared to an active Ethernet network card that is often used in servers . The task of this card is to execute computationally intensive operations on the TOE and thus to relieve the CPU of the server.
Another interesting further development of the HBA in connection with Fiber Channel over Ethernet is the Converged Network Adapter (CNA), which is used to connect end devices directly to the FCoE fabric. Such an adapter provides both fiber channel host bus adapter and classic network interface card functions on one piece of hardware.
The best-known manufacturers of HBA and TOE cards include Adaptec , QLogic , JNI, LSI (Engenio) , Alacritech and Emulex .
