SATA standard performance features
Besides moving to a layered structure, many new performance enhancements have been added to the SATA standard to help meet market requirements for additional storage functionality. Some of these new features include Native Command Queuing (NCQ), Link Power Management, Hot plug support, Port Multiplier, Port Selector, and External SATA.

I. Native Command Queuing
NCQ is one of the most advanced and highly anticipated features introduced into the Serial ATA standard. It's a powerful interface technology designed to increase performance and endurance by allowing the drive to internally optimize the execution order of workloads.

Intelligent reordering of commands within the drive's internal command queue helps improve performance of queued workloads by minimizing mechanical positioning latencies on the drive. Native Command Queuing achieves high performance and efficiency through efficient command re-ordering. In addition, there are new capabilities built into the SATA protocol to enhance NCQ performance which now include race-free status return, interrupt aggregation, first-party DMA (FPDMA), and priority handling.

II. Link Power Management
Serial ATA has three different power modes which are controlled by the Device and Host controller. The different modes of power include PHY ready, partial, and slumber. The partial and slumber modes are energy saving modes for power sensitive applications and for improvement in battery life while generating less heat. These low power modes for the link are initiated by the Host or the Device.

III. Hot plug support
"Hot plug" is defined simply as the ability to connect and disconnect devices without prior notification to the system. This provides system flexibility and ease of use, as well as an easy way to replace, upgrade, or expand storage without incurring downtime. There's no need to power down the interface prior to replacing devices " it's supported by external cables and backplane connectors and eSATA.

IV. Port Multiplier
A Port Multiplier is a mechanism for one active Host connection to communicate with multiple devices. A Port Multiplier can be thought of as a simple "demultiplexer" where one active Host connection is demultiplexed to multiple device connections, as shown in Figure 4. Only one active Host connection to the Port Multiplier is supported. The Port Multiplier is an extensible design that supports up to 15 endpoint device connections and utilizes the full bandwidth of the Host connection.

4. Port Multiplier overview.

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V. Port Selector
A Port Selector allows two different Host ports to connect to the same Device in order to create a redundant path to that Device. In combination with a Redundant Array of Independent Drives (RAID), the Port Selector allows system providers to build fully redundant solutions. The upstream ports of a Port Selector may also be attached to a Port Multiplier to provide redundancy in a more complex topology. A Port Selector can be thought of as a simple multiplexer as shown in Figure 5.

5. Port Selector overview.

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VI. External SATA
External SATA (eSATA) solutions have two major SATA connections using shielded cables and connectors. It enables an external direct attached storage for notebooks, desktops, consumer electronics, and entry servers with high performance, cost effective expansion storage. eSATA enables new usage models outside of the box with up to six times faster than existing external storage solutions: USB 2.0, 1394 based on robust and user friendly external connection.

SATA implementation examples: Host and Device controllers
Mentor Graphics offers two examples of the SATA interface with either a Host or Device controller configuration, along with a PHY layer. Mentor's SATA Host controller can be implemented to map the SATA protocol layers functionality from the host side in an embedded SOC implementation environment.

As designed, the SATA Host controller sits between a Host system and the standard SATA physical layer (SATA PHY). The SATA PHY is responsible for sending packets from the SATA Host controller to the SATA link. The SATA Host controller also has two AHB connections on the Host system bus along with a master connection to allow DMA to start memory read/write operations.

Conversely, the SATA Device controller core is designed to interface to a device CPU and DMA interface on one end, and the SATA Physical Layer controller on the other end. The Application Layer controller, Transport Layer controller, and Link Layer controller are the three core sub-modules that control the overall operation. These three modules coordinate their actions and utilize resources to transfer data between a Device system and a Host system on the other end.

Conclusion
As the successor to PATA, the SATA standard promises to address many of the more critical issues that face design teams today. Mainly, higher transfer speeds, thinner cables/connectors, conserving of battery life, and the ability to hot plug " all while providing better and more reliable operation to the end user.

Without question, we will see the continued evolution and successful adoption of the SATA standard. The storage technology sector has done its part in meeting the increased demand for digital storage and in the process has helped keep our digital age alive and well.

About the Author:
Mohamed A. Salem is the engineering manager of Mentor Graphics intellectual property division.