Introduction to SATA Express (Serial ATA Express)

Overview of SATA Express

What is SATA Express? It is short for Serial ATA Express and sometimes it can be unofficially shortened to SATAe. As a computer bus interface, SATA Express supports both Serial ATA (SATA) and PCI Express (PCIe) storage devices that were originally standardized in the SATA 3.2 specification.

The SATA Express connector used on the host side is backward compatible with standard SATA data connectors. It offers two PCI Express lanes as pure PCI Express connections with storage devices, too.

History

SATA is one of the interfaces of SSD, but with the faster interface required by the hard drive, the speed of the SATA needs to be improved. After evaluating different methods to increase the speed, the designers of the SATA interface found that expanding the SATA interface to double the natural speed to 12 Gbit/s would take more than two years and was very troublesome. Therefore, this method is not suitable for catching up with the advancements in SSD technology.

Finally, the designers of SATA Express chose PCI Express as part of the SATA 3.2 version standardized in 2013. While expanding the SATA specification, a PCI Express interface was also provided in the same backward-compatible connector. By reusing existing technologies, faster speeds can be achieved.

Availability

• In December 2013, ASUS launched a prototype “Z87-Deluxe/SATA Express” motherboard based on the Intel Z87 chipset.
• In April 2014, ASUS also showed some pre-production SATA Express hardware that supports the so-called separate reference clock with independent spread spectrum clocking (SRIS).
• In May 2014, Intel’s Z97 and H97 chipsets were launched, supporting both SATA Express and M.2. The latter is a specification for flash-based storage devices in the form of internal computer expansion cards.
• In late August 2014, the Intel X99 chipset was launched, providing support for SATA Express and M.2.
• In early March 2017, AMD Ryzen went on the market and brought native support for SATA Express to the AMD Socket AM4 platform by using its accompanying X370, X300, B350, A320, and A300 chipsets.

Features

The SATA Express interface exposes two PCI Express 2.0 or 3.0 lanes and two SATA 3.0 (6 Gbit/s) ports through the same host-side SATA Express connector (but not both at the same time), thereby supporting PCI Express and SATA storage devices. The exposed PCI Express lanes provide a pure PCI Express connection between the host and the storage device without an additional bus abstraction layer.

Choosing PCI Express can also expand the performance of the SATA Express interface by using multiple channels and different versions of PCI Express. In more detail, using two PCI Express 2.0 lanes can provide a total bandwidth of 1000 MB/s (2×5 GT/s raw data rate and 8b/10b encoding), while using two PCI Express 3.0 lanes can provide 1969 MB/s (2×8 GT/s raw data rate and 128b/130b encoding). In contrast, the 6 Gbit/s raw bandwidth of SATA 3.0 is effectively equal to 600 MB/s (6 GT/s raw data rate and 8b/10b encoding).

Connectors

There are five types of SATA Express connectors, differing by their position and uses:

• The host plug is used on the motherboard and additional controllers. The connector is backward compatible by accepting traditional standard SATA data cables, allowing the host plug to provide connections for up to two SATA devices.
• The host cable receptacle is the connector on the host-side of the SATA Express cable. This connector is not backward compatible.
• The device cable receptacle is the device side connector on the SATA Express cable, which can be backward compatible by accommodating a SATA device.
• The device plug is used on SATA Express devices. By allowing SATA Express devices to be plugged into U.2 backplanes or MultiLink SAS receptacles, the connector is partially backward compatible. However, SATA Express devices connected in this way can only work when the host supports PCI Express devices.
• The host receptacle is used on the backplane and can be directly matched with SATA Express devices to realize the cable-free connection. By accepting a SATA device, this connector is backward compatible.

Compatibility

By fully supporting traditional SATA 3.0 (6 Gbit/s) storage devices, both at the electrical level and through the required operating system support, the device-level backward compatibility of SATA Express can be ensured.

Bottom Line

To sum up, this post has given you a full introduction to SATA Express. After reading this post, you should know its history, features, connectors, as well as its compatibility.