What is Host Bus Adapters?

The hardware of a computer is made up many different parts. With rapid technological advancements taking place new additions are being made to the computer hardware. One of the most essential parts in computer hardware is a host bus adapter.

This particular piece of hardware is also known as a host controller or simply a host adapter. Generally you will find it being referred to as HBA, which is short for Host Bus Adapters. The basic function of HBA is to connect a host system which is the computer to other existing network and storage devices. These terms are generally used to refer to different devices for connecting Fiber channel and e-SATA, SCSI along with USB, FireWire, Ethernet are all referred to as host adapters.

Each day brings about new changes and we find the umbrella of host bus adapters to be widening to include items that were not previously counted as host adapters. One such recent invention is the result of i-SCSI which brought about the Ethernet host bus adapters. These adapters were very different from the old school Ethernet NICs. This is because they included hardware i-SCSI TCP offload engines.

Host Bus Adapters

The host adapter for SCSI connects a SCSI bus to the computer. The SCSI bus is separated from the host computer’s internal bus through chasm that is bridged with the use of the host adapter. Today you will find host adapters to be embedded with the electronics and firmware that enable it to execute SCSI transactions. They often include a BIOS as well which only grants access to the host system for booting from a SCSI devise. At the same time it helps to configure the host adapter. The host adapter itself is controlled by a device driver that is linked to the operating system.

You will find that each device has a unique numerical ID assigned to it in a typical parallel SCSI subsystem. The rule is set such that a host adapter always appears as SCSI ID7. This gives it the top most priority on the SCSI bus. The priority however descends according to the level of the SCSI ID.
The host adaptor also issues commands to other SCSI devices. In this respect it can be considered to be the SCSI initiator. There is not such restriction on a computer to contain only one host adapter. Rather a computer can contain a number of host adapters which serves to the benefit of the user as it can then increase the number of SCSI devices that are available.

Some of the top brand names involved in the production of host bus manufacturers are ATTO Technology, HP, LSI and Adaptec. The latest adapters being offered by these companies can fit in the likes of the new Apple Mac as well as the Intel PCs and other low profile motherboards from manufacturers such as HP.

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