SATA Express is a specification for a new connector type that enables the routing of both PCIe® and SATA signals. SATA Express is not a command or signaling protocol. It should really be thought of as a connector that mates with legacy SATA cables and new PCIe cables.
SATA Express was developed to help smooth the transition from the legacy SATA interface to the new PCIe interface. SATA Express gives system vendors a common connector that supports both traditional SATA and PCIe signaling and helps OEMs streamline connector inventory and reduce related costs.
One of the misconceptions about SATA Express is that it’s a protocol specification. Rather, as I mentioned, it’s a mechanical specification for a connector and the matching cabling. Protocols that support SATA Express include SATA, AHCI and NVME.
SATA Express defines connectors for both a 2.5” drive and the host system. SATA Express connects the drive and system using SATA cables or the newly defined PCIe cables.
SATA Express supports both SATA and PCIe signaling as well as the legacy SATA connectors, there are multiple configuration options available to motherboard and device manufacturers. The image below shows plug
(A) which is built for attaching to a PCIe device. Socket
(B) would be part of a cable assembly for receiving plug (a) or a standard SATA plug, and Socket
(C) would mount to a backplane or motherboard fir receiving plug (a) or a standard SATA plug.
(D)The last two connectors are a mating pair designed to enable cabling (e) to connect to motherboards (d).
SATA Express blends the names of the two connectors and captures the hybridization of the physical interconnects. The name reflects the ability of legacy SATA connectors to support higher PCIe data rates to simplify the transition to PCIe devices. SATA Express can pull double duty, supporting both PCIe and SATA signaling in the same motherboard socket. The same SATA Express socket accepts both traditional SATA and new PCIe cables and links to either a legacy SATA or SATA Express device connector.
The PCIe interface defines the top SATA Express speed. A PCIe Gen2 x2 device supports up to 900 MB/s of throughput, a PCIe Gen3 x2 device up to 1800 MB/s of throughput – both significantly higher than 550 Mb/s speed ceiling of today’s SATA devices.
SATA Express was born of the stuff of all great inventions. Necessity. The challenge SATA-IO faced in doubling SATA 6 Gb/s speeds was herculean. The undertaking would have been too time-consuming to support the next-generation connection speeds that PCIe answers. It would have been too involved, requiring an overhaul of the SATA standard. Even in the brightest scenario, the effort would have produced a power guzzler at a time when greater power efficiency is a must for system builders. SATA-IO found a better path, an elegant bridge to PCIe speeds in the form of SATA Express.
| SATA Express host cable receptacle | SATA Express device cable receptacle | SATA Express host receptacle | SATA cable receptacle | SFF-8639 backplane receptacle | SAS MultiLink Receptacle | |
|---|---|---|---|---|---|---|
| SATA Express host plug | Yes | No | No | Yes | No | No |
| SATA Express device plug | No | Yes | Yes | No | Yes | Yes |
| SATA device plug | No | Yes | Yes | Yes | Yes | Yes |
Compatibility
Backward compatibility is ensured by fully supporting legacy SATA 3.0 6 Gbit/s storage devices, both on the electrical level and on the software (operating system support) level. Mechanically, connectors on the host side are keeping their backward compatibility in a way similar to how it was achieved with USB 3.0, by forming the new host connector with an additional connector "stacked" on top of two legacy 3.5-inch SATA data connectors.
On the host side, SATA Express interface provides two SATA 3.0 6 Gbit/s ports, paired with the host plug backward compatible with the standard 3.5-inch SATA data connectors. This ensures the possibility for attaching legacy SATA devices to hosts equipped with SATA Express controllers.
Backward compatibility for the operating systems supporting SATA drives is provided through legacy AHCI controller interface support, as visible from the operating system perspective. Access through the AHCI driver is ensured for both SATA SSDs and PCI Express SSDs.[4] Though, there is a penalty of not delivering optimal performance by using AHCI for accessing PCI Express SSDs.
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