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SATA Express (sometimes unofficially shortened to SATAe) is a
computer bus In computer architecture, a bus (historically also called a data highway or databus) is a communication system that transfers data between components inside a computer or between computers. It encompasses both hardware (e.g., wires, optical ...
interface that supports both
Serial ATA SATA (Serial AT Attachment) is a computer bus interface that connects host adapter, host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. Serial ATA succeeded the earlier Parallel ATA (PAT ...
(SATA) and
PCI Express PCI Express (Peripheral Component Interconnect Express), officially abbreviated as PCIe, is a high-speed standard used to connect hardware components inside computers. It is designed to replace older expansion bus standards such as Peripher ...
(PCIe) storage devices, initially standardized in the SATA 3.2 specification. The SATA Express connector used on the host side is
backward compatible In telecommunications and computing, backward compatibility (or backwards compatibility) is a property of an operating system, software, real-world product, or technology that allows for interoperability with an older legacy system, or with inpu ...
with the standard SATA data connector, while it also provides two PCI Express lanes as a pure PCI Express connection to the storage device. Instead of continuing with the SATA interface's usual approach of doubling its native speed with each major version, SATA 3.2 specification included the PCI Express bus for achieving data transfer speeds greater than the SATA 3.0 speed limit of 6 
Gbit/s In telecommunications, data transfer rate is the average number of bits ( bitrate), characters or symbols ( baudrate), or data blocks per unit time passing through a communication link in a data-transmission system. Common data rate units are mu ...
. Designers of the SATA interface concluded that doubling the native SATA speed would take too much time to catch up with the advancements in
solid-state drive A solid-state drive (SSD) is a type of solid-state storage device that uses integrated circuits to store data persistently. It is sometimes called semiconductor storage device, solid-state device, or solid-state disk. SSDs rely on non- ...
(SSD) technology, would require too many changes to the SATA standard, and would result in a much greater power consumption compared with the existing PCI Express bus. As a widely adopted computer bus, PCI Express provides sufficient bandwidth while allowing easy scaling up by using faster or additional lanes. In addition to supporting legacy Advanced Host Controller Interface (AHCI) at the logical interface level, SATA Express also supports
NVM Express NVM Express (NVMe) or Non-Volatile Memory Host Controller Interface Specification (NVMHCIS) is an open, logical-device interface functional specification, specification for accessing a computer's non-volatile storage media usually attached via th ...
(NVMe) as the logical device interface for attached PCI Express storage devices. While the support for AHCI ensures software-level backward compatibility with legacy SATA devices and legacy
operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...
s, NVM Express is designed to fully utilize high-speed PCI Express storage devices by leveraging their capability of executing many I/O operations in parallel.


History

The Serial ATA (
SATA SATA (Serial AT Attachment) is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. Serial ATA succeeded the earlier Parallel ATA (PATA) standard ...
) interface was designed primarily for interfacing with
hard disk drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating hard disk drive platter, pla ...
s (HDDs), doubling its native speed with each major revision: maximum SATA transfer speeds went from 1.5 Gbit/s in SATA 1.0 (standardized in 2003), through 3 Gbit/s in SATA 2.0 (standardized in 2004), to 6 Gbit/s as provided by SATA 3.0 (standardized in 2009). SATA has also been selected as the interface for gradually more adopted solid-state drives ( SSDs), but the need for a faster interface became apparent as the speed of SSDs and
hybrid drive A hybrid drive (solid state hybrid drive – SSHD, and dual-storage drive) is a logical or physical computer storage device that combines a faster storage medium such as solid-state drive (SSD) with a higher-capacity hard disk drive (HDD). Th ...
s increased over time. As an example, some SSDs available in early 2009 were already well over the capabilities of SATA 1.0 and close to the SATA 2.0 maximum transfer speed, while in the second half of 2013 high-end consumer SSDs had already reached the SATA 3.0 speed limit, requiring an even faster interface. While evaluating different approaches to the required speed increase, designers of the SATA interface concluded that extending the SATA interface so it doubles its native speed to 12 Gbit/s would require more than two years, making that approach unsuitable for catching up with advancements in SSD technology. At the same time, increasing the native SATA speed to 12 Gbit/s would require too many changes to the SATA standard, ending up in a more costly and less power efficient solution compared with the already available and widely adopted PCI Express bus. Thus, PCI Express was selected by the designers of SATA interface, as part of the SATA 3.2 revision that was standardized in 2013; extending the SATA specification to also provide a PCI Express interface within the same backward-compatible connector allowed much faster speeds by reusing already existing technology. Some vendors also use proprietary logical interfaces for their flash-based storage products, connected through the PCI Express bus. Such storage products can use a multi-lane PCI Express link, while interfacing with the operating system through proprietary drivers and host interfaces. Moreover, there are similar storage products using NVM Express as the non-proprietary logical interface for a PCI Express add-on card.


Availability

Support for SATA Express was initially announced for the Intel 9 Series chipsets, Z97 and H97 Platform Controller Hubs (PCHs), with both of them supporting Intel Haswell and Haswell Refresh processors; availability of these two chipsets was planned for 2014. In December 2013,
Asus ASUSTeK Computer Inc. (, , , ; stylized as ASUSTeK or ASUS) is a Taiwanese Multinational corporation, multinational computer, phone hardware and electronics manufacturer headquartered in Beitou District, Taipei, Taiwan. Its products include deskto ...
unveiled a prototype " Z87-Deluxe/SATA Express"
motherboard A motherboard, also called a mainboard, a system board, a logic board, and informally a mobo (see #Nomenclature, "Nomenclature" section), is the main printed circuit board (PCB) in general-purpose computers and other expandable systems. It ho ...
based on the Intel Z87 chipset, supporting Haswell processors and using additional ASMedia controller to provide SATA Express connectivity; this motherboard was also showcased at CES 2014 although no launch date was announced. In April 2014, Asus also demonstrated support for the so-called ''separate reference clock with independent
spread spectrum In telecommunications, especially radio communication, spread spectrum are techniques by which a signal (electrical engineering), signal (e.g., an electrical, electromagnetic, or acoustic) generated with a particular Bandwidth (signal processi ...
clocking'' (SRIS) with some of its pre-production SATA Express hardware. SRIS eliminates the need for complex and costly shielding on SATA Express cables required for transmitting PCI Express synchronization signals, by providing a separate
clock generator A clock generator is an electronic oscillator that produces a clock signal for use in synchronizing a circuit's operation. The output clock signal can range from a simple symmetrical square wave to more complex arrangements. The basic parts tha ...
on the storage device with additional support from the motherboard
firmware In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, h ...
. In May 2014, Intel Z97 and H97 chipsets became available, bringing support for both SATA Express and M.2, which is a specification for flash-based storage devices in form of internally mounted computer expansion cards. Z97 and H97 chipsets use two PCI Express 2.0 lanes for each of their SATA Express ports, providing 1  GB/s of bandwidth to PCI Express storage devices. The release of these two new chipsets, intended primarily for high-end desktops, was soon followed by the availability of Z97- and H97-based motherboards. In late August 2014, Intel X99 chipset became available, bringing support for both SATA Express and M.2 to the Intel's enthusiast platform. Each of the X99's SATA Express ports requires two PCI Express 2.0 lanes provided by the chipset, while the M.2 slots can use either two 2.0 lanes from the chipset itself, or up to four 3.0 lanes taken directly from the LGA 2011-v3 CPU. As a result, the X99 provides bandwidths of up to 3.94 GB/s for connected PCI Express storage devices. Following the release of X99 chipset, numerous X99-based motherboards became available. In early March 2017,
AMD Advanced Micro Devices, Inc. (AMD) is an American multinational corporation and technology company headquartered in Santa Clara, California and maintains significant operations in Austin, Texas. AMD is a hardware and fabless company that de ...
Ryzen Ryzen ( ) is a brand of multi-core x86-64 microprocessors, designed and marketed by AMD for desktop, mobile, server, and embedded platforms, based on the Zen microarchitecture. It consists of central processing units (CPUs) marketed for mai ...
became available, bringing native support for SATA Express to the AMD Socket AM4 platform, through use of its accompanying X370, X300, B350, A320 and A300 chipsets. Ryzen also supports M.2 and other forms of PCI Express storage devices, using up to the total of eight PCI Express 3.0 lanes provided by the chipset and the AM4 CPU. As a result, Ryzen provides bandwidths of up to 7.88 GB/s for connected PCI Express storage devices. As a form factor, SATA Express is considered a failed standard, because when SATA Express was introduced, the M.2 form factor and
NVMe NVM Express (NVMe) or Non-Volatile Memory Host Controller Interface Specification (NVMHCIS) is an open, logical-device interface specification for accessing a computer's non-volatile storage media usually attached via the PCI Express bus. The in ...
standards were also launched, gaining much larger popularity than Serial ATA and SATA Express. Not many storage devices utilizing the SATA Express interface were released for consumers, and SATA Express ports quickly disappeared from new motherboards.


Features

SATA Express interface supports both PCI Express and SATA storage devices by exposing 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). Exposed PCI Express lanes provide a pure PCI Express connection between the host and storage device, with no additional layers of bus abstraction. The SATA revision 3.2 specification, in its gold revision , standardizes the SATA Express and specifies its hardware layout and electrical parameters. The choice of PCI Express also enables scaling up the performance of SATA Express interface by using multiple lanes and different versions of PCI Express. In more detail, using two PCI Express 2.0 lanes provides 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 provides 1969 MB/s (2 × 8 GT/s raw data rate and 128b/130b encoding). In comparison, the 6 Gbit/s raw bandwidth of SATA 3.0 equates effectively to 600 MB/s (6 GT/s raw data rate and 8b/10b encoding). There are three options available for the logical device
interfaces Interface or interfacing may refer to: Academic journals * ''Interface'' (journal), by the Electrochemical Society * '' Interface, Journal of Applied Linguistics'', now merged with ''ITL International Journal of Applied Linguistics'' * '' Inter ...
and command sets used for interfacing with storage devices connected to a SATA Express controller: ; Legacy SATA : Used for
backward compatibility In telecommunications and computing, backward compatibility (or backwards compatibility) is a property of an operating system, software, real-world product, or technology that allows for interoperability with an older legacy system, or with Input ...
with legacy SATA devices, and interfaced through the AHCI driver and legacy SATA 3.0 (6 Gbit/s) ports provided by a SATA Express controller. ; PCI Express using AHCI : Used for PCI Express SSDs and interfaced through the
AHCI The Advanced Host Controller Interface (AHCI) is a technical standard defined by Intel that specifies the Hardware register, register-level interface of Serial ATA (SATA) host controllers in a non-implementation-specific manner in its Intel chip ...
driver and provided PCI Express lanes, providing backward compatibility with widespread SATA support in operating systems at the cost of not delivering optimal performance by using AHCI for accessing PCI Express SSDs. AHCI was developed back at the time when the purpose of a host bus adapter (HBA) in a system was to connect the CPU/memory subsystem with a much slower storage subsystem based on rotating magnetic media; as a result, AHCI has some inherent inefficiencies when applied to SSD devices, which behave much more like
DRAM Dram, DRAM, or drams may refer to: Technology and engineering * Dram (unit), a unit of mass and volume, and an informal name for a small amount of liquor, especially whisky or whiskey * Dynamic random-access memory, a type of electronic semicondu ...
than like spinning media. ; PCI Express using NVMe : Used for PCI Express SSDs and interfaced through the
NVMe NVM Express (NVMe) or Non-Volatile Memory Host Controller Interface Specification (NVMHCIS) is an open, logical-device interface specification for accessing a computer's non-volatile storage media usually attached via the PCI Express bus. The in ...
driver and provided PCI Express lanes, as a high-performance and scalable host controller interface designed and optimized especially for interfacing with PCI Express SSDs. NVMe has been designed from the ground up, capitalizing on the low latency and parallelism of PCI Express SSDs, and complementing the parallelism of contemporary CPUs, platforms and applications. At a high level, primary advantages of NVMe over AHCI relate to NVMe's ability to exploit parallelism in host hardware and software, based on its design advantages that include data transfers with fewer stages, greater depth of command queues, and more efficient
interrupt In digital computers, an interrupt (sometimes referred to as a trap) is a request for the processor to ''interrupt'' currently executing code (when permitted), so that the event can be processed in a timely manner. If the request is accepted ...
processing.


Connectors

Connectors used for SATA Express were selected specifically to ensure backward compatibility with legacy SATA devices where possible, without the need for additional adapters or converters. The connector on the host side accepts either one PCI Express SSD or up to two legacy SATA devices, by providing either PCI Express lanes or SATA 3.0 ports depending on the type of connected storage device. There are five types of SATA Express connectors, differing by their position and purpose: * ''Host plug'' is used on motherboards and add-on controllers. This connector is
backward compatible In telecommunications and computing, backward compatibility (or backwards compatibility) is a property of an operating system, software, real-world product, or technology that allows for interoperability with an older legacy system, or with inpu ...
by accepting legacy standard SATA data cables, resulting in the host plug providing connectivity for up to two SATA devices. * ''Host cable receptacle'' is the host-side connector on SATA Express cables. This connector is not backward compatible. * ''Device cable receptacle'' is the device-side connector on SATA Express cables, backward compatible by accepting one SATA device. * ''Device plug'' is used on SATA Express devices. This connector is partially backward compatible by allowing SATA Express devices to be plugged into
U.2 U.2 (pronounced "U-dot-2"), formerly known as SFF-8639, is a computer interface standard used to connect solid-state drives (SSDs) to a computer. It defines the physical connector, electrical characteristics, and supported communication protocol ...
backplanes or
MultiLink SAS In computing, Serial Attached SCSI (SAS) is a point-to-point serial Communications protocol, protocol that moves data to and from Computer storage, computer-storage devices such as hard disk drives, solid-state drives and tape drives. SAS replac ...
receptacles; however, a SATA Express device connected that way will be functional only if the host supports PCI Express devices. * ''Host receptacle'' is used on backplanes for mating directly with SATA Express devices, resulting in cableless connections. This connector is backward compatible by accepting one SATA device. The above listed SATA Express connectors provide only two PCI Express lanes, as the result of overall design focusing on a rapid low-cost platform transition. That choice allowed easier backward compatibility with legacy SATA devices, together with making it possible to use cheaper unshielded cables. , some NVM Express devices in form of 2.5-inch drives use the ''U.2'' connector (originally known as ''SFF-8639'', with the renaming taking place in June 2015), which is expected to gain broader acceptance. The U.2 connector is mechanically identical to the SATA Express device plug, but provides four PCI Express lanes through a different usage of available pins. The table below summarizes the compatibility of involved connectors.


Compatibility

Device-level
backward compatibility In telecommunications and computing, backward compatibility (or backwards compatibility) is a property of an operating system, software, real-world product, or technology that allows for interoperability with an older legacy system, or with Input ...
for SATA Express is ensured by fully supporting legacy SATA 3.0 (6 Gbit/s) storage devices, both on the electrical level and through the required
operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...
support. Mechanically, connectors on the host side retain their backward compatibility in a way similar to how USB 3.0 does it the new host-side SATA Express connector is made by "stacking" an additional connector on top of two legacy standard SATA data connectors, which are regular SATA 3.0 (6 Gbit/s) ports that can accept legacy SATA devices. This backward compatibility of the host-side SATA Express connector, which is formally known as the host plug, ensures the possibility for attaching legacy SATA devices to hosts equipped with SATA Express controllers. Backward compatibility on the software level, provided for legacy operating systems and associated
device driver In the context of an operating system, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton. A driver provides a software interface to hardware devices, enabli ...
s that can access only SATA storage devices, is achieved by retaining support for the AHCI controller interface as a legacy logical device interface, as visible from the operating system perspective. Access to storage devices using AHCI as a logical device interface is possible for both SATA SSDs and PCI Express SSDs, so operating systems that do not provide support for NVMe can optionally be configured to interact with PCI Express storage devices as if they were legacy AHCI devices. However, because NVMe is far more efficient than AHCI when used with PCI Express SSDs, SATA Express interface is unable to deliver its maximum performance when AHCI is used to access PCI Express storage devices; see above for more details.


See also

* List of device bandwidths * M.2 (formerly known as the Next Generation Form Factor) *
Serial attached SCSI In computing, Serial Attached SCSI (SAS) is a point-to-point serial Communications protocol, protocol that moves data to and from Computer storage, computer-storage devices such as hard disk drives, solid-state drives and tape drives. SAS replac ...
(SAS)


Notes


References


External links

* Official (SATA-IO) website
LFCS: Preparing Linux for nonvolatile memory devices
LWN.net, April 19, 2013, by Jonathan Corbet
NVMe vs AHCI: Another Win for PCIe
AnandTech ''AnandTech'' was an online computer hardware magazine owned by Future plc. It was founded in April 1997 by then-14-year-old Anand Lal Shimpi, who was CEO and editor-in-chief until August 2014, with Ryan Smith replacing him as editor-in-chief. ...
, March 13, 2014, by Kristian Vatto
Intel SSD DC P3700 Review: Understanding NVM Express
Tom's Hardware ''Tom's Hardware'' is an online publication owned by Future plc and focused on technology. It was founded in 1996 by Thomas Pabst. It provides articles, news, price comparisons, videos and reviews on computer hardware and high technology. The s ...
, August 13, 2014, by Drew Riley
PCIe SSD 101: An Overview of Standards, Markets and Performance
SNIA, August 2013, archived from the original on February 2, 2014 * US patent 20130294023, November 7, 2013, assigned to Raphael Gay
MultiLink SAS presentations, press releases and roadmaps
SCSI Trade Association {{Solid-state drive 2013 introductions Computer buses Serial ATA Serial buses Computer connectors Motherboard expansion slot