Port multiplier

SATA 2.0 controller with built-in SATA port multipliers

Port multiplier

A port multiplier is a device that allows multiple SATA (Serial ATA) devices to be connected to a single SATA host port. This technology is particularly useful in scenarios where the number of available SATA ports is limited, such as in small form factor computers or embedded systems.

Functionality

Port multipliers operate by using a single SATA port on the host controller and expanding it to multiple SATA devices. This is achieved through a process known as multiplexing, where the data from multiple devices is combined and transmitted over a single connection. The host controller communicates with the port multiplier, which in turn manages the communication with the individual SATA devices.

Types of Port Multipliers

There are two main types of port multipliers:

• Command-based port multipliers: These devices allow the host controller to send commands to multiple devices simultaneously. They are more efficient and provide better performance compared to the other type.
• FIS-based port multipliers: These devices use Frame Information Structures (FIS) to manage data transfer between the host and the devices. They are generally simpler and less expensive but may not offer the same level of performance as command-based port multipliers.

Applications

Port multipliers are commonly used in various applications, including:

• RAID (Redundant Array of Independent Disks) configurations, where multiple drives are used to improve performance or provide data redundancy.
• NAS (Network Attached Storage) devices, which require multiple drives to store large amounts of data.
• Embedded systems and small form factor computers, where space and the number of available ports are limited.

Limitations

While port multipliers offer significant advantages, they also have some limitations:

• Performance: The total bandwidth of the single SATA port is shared among all connected devices, which can lead to reduced performance, especially when multiple devices are active simultaneously.
• Compatibility: Not all SATA controllers support port multipliers, and compatibility can vary between different models and manufacturers.

Related Technologies

• SATA Express
• eSATA
• USB
• Thunderbolt (interface)

See Also

• Serial ATA
• RAID
• Network Attached Storage
• Embedded system