What Is A Storage SCSI Controller And How Does It Work

A SCSI controller or more commonly known as a host adapter is a device that is used to connect a computer to different SCSI devices. These connectors can be both internal and external, and while the internal SCSI connectors are installed directly in the computer, the external host adapters are connected to the computer via a cable.

A storage SCSI controller works by sending commands to different SCSI devices connected to the bus. These commands direct the different connected devices to either read or write data. A compatible SCSI controller also manages the flow of data between the SCSI peripherals and the computer.

Types of SCSI Controllers

The SCSI controllers have a lot of different types depending upon various factors such as speed, bus width, protocol, and connector of the SCSI devices they support. Some of the most commonly used types of storage SCSI controllers are:

SCSI 1: It is the first version among the SCSI storage solutions. This type can support a data transfer rate of about 5 MB/s and a bus width of 8 bits. The SCSI 1 can also support a maximum cable length of  6 meters. The SCSI 1 version of the controller uses a connector of 50 pins.

SCSI 2: After the SCSI 1 the improved version came with the name SCSI 2. It had a whopping double data transfer rate of up to 10 MB/s and a bus width that ranged up to 16 bits. It can use both 50-pin and 68-pin connectors. The new SCSI 2 also came with exciting features like command queuing, and SCSI parity.

SCSI 3: It supports a data transfer rate of up to 80 MB/s, a bus width of 8 or 16 bits. The third version can support a cable length of up to 25 meters. It can also use a variety of connectors and protocols, such as serial bus protocol (SBP), fiber channel protocol (FCP), and much more.

SAS: This is not a separate type but a subtype of SCSI-3 and uses a serial point-to-point connection instead of a parallel bus. It supports a data transfer rate of up to 12 GB/s, bus width of one or two lanes per device. It uses a 29-pin connector and a serial bus protocol.

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Some Fun Facts About SCSI Host Bus Adapter

• SCSI controllers can support up to 15 devices on a single bus.
• The SCSI bus can transfer data at speeds of up to 160 MB/s.
• SCSI controllers are often used in servers and workstations.
• SCSI is a legacy technology, and it has been largely replaced by SATA and NVMe in recent years.