What Is a Host Bus Adapter

A host bus adapter (HBA) is a critical component in a computer system that allows devices to communicate with an operating system and the central processing unit (CPU). The computer’s motherboard integrates some host adapters onboard (e.g., storage drive adapters) and other components contain their own HBA (e.g., video expansion cards).

What Is a Host Bus Adapter?

The CPU processes all input and output for a computer, but every component needs a host bus adapter to communicate between the operating system and the CPU. A host bus adapter is part of every peripheral connected to the computer. Whether you add a new storage drive or upgrade your video card to the latest GPU, all components have an HBA integrated on the circuit board or use the HBA integrated with the computer’s motherboard.

Types of host bus adapters depend on their functionality. A common HBA for storage drives is a Serial Advanced Technology Attachment (SATA), and a common HBA for network cards is Ethernet. The type that you use determines the way a component communicates with your computer. SATA and Ethernet cards require cables, but other components such as a video card or sound card connect to expansion slots on the motherboard.

How Do Host Bus Adapters Work?

Think of the host adapter as a communication bridge between input from the operating system and the central processing unit. Every function goes through the CPU, and the HBA is responsible for creating a communication channel between the component and the CPU. The CPU processes input from the component and sends back output for the component to use and display to the user via the operating system. Without the HBA, the component would not be able to provide its functionality to your computer.

Component manufacturers design their interface cards for maximum performance to support the latest speeds and standards. As an example, a video card has several circuits installed on the board with the HBA, GPU, and interface connections (e.g., DisplayPort or HDMI). Other circuits installed on the board handle input and output, and most components have various transistors, capacitors, diodes, sensors, and resistors to handle power and electronic signals.

Why Would You Use a Host Bus Adapter?

A computer must have a host bus adapter for every input and output device that communicates with the operating system. Component manufacturers integrate HBAs with their devices, so administrators do not need to worry about having an HBA compatible with a new expansion card. Some components do not come with a connection cable, so administrators must buy cables to connect devices to the computer’s motherboard when they buy the expansion card.

Every new generation of host bus adapters improves performance, but usually, it’s backward compatible with older motherboards. For example, the older Small Computer System Interface (SCSI) was replaced by SATA, but older computers might support both HBA types. The introduction of SATA improved the speed of data transfers between the operating system and storage devices.

Older generations of HBAs might no longer be compatible with newer generations of computers. When you buy a computer component such as a storage drive or video card, the component must have the right HBA to connect with your computer. For example, a newer SATA storage device cannot connect to an SCSI adapter. Newer host adapters improve performance of the computer so that you can scale. Adding new components to a server scales it up so that it can support newer technology and functionality.

Host Bus Adapters for SAN

A large enterprise or data centre might have a storage area network (SAN) to support several interconnected drives for large storage capacity. A SAN uses high-performance Fibre Channels for data transfers between servers and storage drives. Data centers use SANs to support enterprise customer cloud backups, disaster recovery, and application data. An enterprise customer could have potentially petabytes of data transfers, and a SAN provides the large bandwidth and speed to support instantaneous processing.

The fibre cards installed in a SAN environment use an HBA to connect the storage drives with the network. A fibre cable connects the storage device network card to the network so that servers and other infrastructure can communicate with the SAN. The HBA for the storage device might be integrated on the motherboard, or it can plug into a slot (e.g., PCI Express slot) on a server’s motherboard. Without the HBA, the fibre cable and expansion card would not be able to communicate with the network.

HBA vs. SATA

For older computers, integrated SATA support might not be available on the motherboard. Administrators can choose to install an expansion card in an older server to provide SATA support for storage drives that need it (e.g., solid-state drives). A SATA card installs into a compatible slot (e.g., PCI Express) and provides HBA support for the newer technology.

The SATA card contains an HBA, and it could support multiple storage drives. SATA drives still need a SATA cable to connect them to the motherboard and the expansion card. The SATA cables connect directly to the drives and the expansion card to facilitate communication between the drive and the CPU.

HBA vs. RAID Controller

Similar to a SATA card, a redundant array of independent disks (RAID) also needs an HBA to facilitate communication between drives, the CPU, and the operating system. A RAID HBA is also referred to as a RAID controller, and it could be found integrated directly on a motherboard or as a separate expansion card. RAID controllers are used for multiple drives that work together to support storage failover—such as RAID 1 used for mirroring—or fast reads and writes such as RAID 0.

A RAID controller used for all the drives in the RAID collection is a form of HBA. The HBA takes input from the operating system and sends the data to the drive to instruct it on what to do with the input. Retrieval of data from the RAID storage must first pass through the HBA to display output to the user.

Conclusion

When you work with servers in a data centre, the administrator installing expansion cards on network servers will ensure that the component has the latest generation of HBA to support speed of processing and data transfers. You can identify HBAs installed in a server by looking at the server's specifications. The specifications usually identify the HBAs and compatible operating systems if necessary.