U.2 (pronounced 'u-dot-2'), formerly known as SFF-8639, is a computer interface standard for connecting

solid-state drive A solid-state drive (SSD) is a solid-state storage device that uses integrated circuit assemblies to store data persistently, typically using flash memory, and functioning as secondary storage in the hierarchy of computer storage. It is a ...

s (SSDs) to a computer. It covers the physical connector, electrical characteristics, and communication protocols. It was developed for the enterprise market and designed to be used with new

PCI Express PCI Express (Peripheral Component Interconnect Express), officially abbreviated as PCIe or PCI-e, is a high-speed serial computer expansion bus standard, designed to replace the older PCI, PCI-X and AGP bus standards. It is the common ...

drives along with SAS and

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 t ...

drives. It uses up to four PCI Express lanes and two SATA lanes.

History

The Enterprise SSD form factor was developed by the SSD Form Factor Working Group (SFFWG). The specification was released on December 20, 2011, as a mechanism for providing PCI Express connections to SSDs for the enterprise market. Goals included being usable in existing 2.5" and 3.5" mechanical enclosures, to be hot swappable and to allow legacy SAS and SATA drives to be mixed using the same connector family. In June 2015, the SFFWG announced that the connector was being renamed to U.2.

Connector

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. U.2 devices may be connected to an

M.2 M.2, pronounced ''m dot two'' and formerly known as the Next Generation Form Factor (NGFF), is a specification for internally mounted computer expansion cards and associated connectors. M.2 replaces the mSATA standard, which uses the PCI Ex ...

port using an adapter.

Availability

In November 2015, Intel introduced the 750 series SSD which is available in both PCI Express and U.2 variants. Since then, U.2 has achieved a high level of support from the major storage vendors and storage appliance suppliers.

U.2 compared with M.2

* U.2 allows hot-swap, whereas

does not. * U.2 can use 3.3V or 12V for power, while M.2 only supports 3.3V.

As implemented

While the U.2 standard does not imply a form factor of the device that uses it, in practice U.2 is used only on 2.5" SSDs. 2.5" drives are typically physically larger than M.2 drives and thus typically have larger capacities.

References