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<h2 id="history">History</h2> <p>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" form factors, to be hot swappable and to allow legacy SAS and SATA drives to be mixed using the same connector family.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> </p><p>In June 2015, the SFFWG announced that the connector was being renamed to U.2.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p> <h2 id="connector">Connector</h2> <p>The U.2 connector is mechanically identical to the <a href="/facts/SATA_Express/sdlgJVJy">SATA Express device plug</a>, but provides four PCI Express lanes through a different usage of available pins.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a><a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> </p><p>U.2 devices may be connected to an <a href="/facts/M.2/E49r6PUm">M.2</a> port using an adapter.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> </p> <h2 id="availability">Availability</h2> <p>In November 2015, Intel introduced the 750 series SSD which is available in both PCI Express and U.2 variants.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p><p>Since then, U.2 has achieved a high level of support from the major storage vendors and storage appliance suppliers. </p> <h2 id="u2-compared-with-m2">U.2 compared with M.2</h2> <p>U.2 can use 3.3 V, 5 V and 12 V for power,<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> while M.2 only supports 3.3 V. </p> <h3>As implemented</h3> <p>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 physically larger than M.2 drives and thus typically have larger capacities. </p> <h2 id="u3">U.3</h2> <p>U.3 (SFF-TA-1001) is built on the U.2 spec and uses the same SFF-8639 connector. A single "tri-mode" (PCIe/SATA/SAS) backplane receptacle can handle all three types of connections; the controller automatically detects the type of connection used. This is unlike U.2, where users need to use separate controllers for SATA/SAS and NVMe. U.3 devices are required to be backwards-compatible with U.2 hosts. U.2 devices are not compatible and cannot be used with U.3 hosts.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Enterprise_and_Data_Center_Standard_Form_Factor/VS6DU2z8">EDSFF</a> – U.2 successor</li> <li><a href="/facts/Hard_disk_drive/kekLSGSE">Hard disk drive</a></li> <li><a href="/facts/M.2/E49r6PUm">M.2</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Burke, Steve. "U.2 vs. M.2 vs. SATA Express Interface Comparison & Speeds". Gamers Nexus. Archived from the original on 15 May 2023. Retrieved 13 January 2022. <a href="https://web.archive.org/web/20230515181847/https://www.gamersnexus.net/guides/2405-u2-vs-m2-vs-sata-express-best-for-ssds" target="_blank">https://web.archive.org/web/20230515181847/https://www.gamersnexus.net/guides/2405-u2-vs-m2-vs-sata-express-best-for-ssds</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>"Enterprise SSD Form Factor version 1.0" (PDF). SSD Form Factor Working Group. 20 December 2011. <a href="http://www.ssdformfactor.org/docs/SSD_Form_Factor_Version1_00.pdf" target="_blank">http://www.ssdformfactor.org/docs/SSD_Form_Factor_Version1_00.pdf</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"SFFWG Renames PCIe SSD SFF-8639 Connector To U.2". Tom's Hardware. 2015-06-05. Retrieved 2017-07-16. <a href="http://www.tomshardware.com/news/sff-8639-u.2-pcie-ssd-nvme,29321.html" target="_blank">http://www.tomshardware.com/news/sff-8639-u.2-pcie-ssd-nvme,29321.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"Figure 37: Pin usage across Existing standards" (PDF). Archived from the original (PDF) on 2016-05-06. Retrieved 2017-07-16. <a href="https://web.archive.org/web/20160506155202/http://www.ssdformfactor.org/docs/SSD_Form_Factor_Version1_a.pdf#page=48" target="_blank">https://web.archive.org/web/20160506155202/http://www.ssdformfactor.org/docs/SSD_Form_Factor_Version1_a.pdf#page=48</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>"U.2 connector pinout". PinoutGuide.com. <a href="http://pinoutguide.com/HD/U.2_SATA_connector_pinout.shtml" target="_blank">http://pinoutguide.com/HD/U.2_SATA_connector_pinout.shtml</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>"Intel bridges the U.2 gap with an M.2 cable for its 750 Series SSD". The Tech Report. Retrieved 2017-07-16. <a href="http://techreport.com/news/30251/intel-bridges-the-u-2-gap-with-an-m-2-cable-for-its-750-series-ssd" target="_blank">http://techreport.com/news/30251/intel-bridges-the-u-2-gap-with-an-m-2-cable-for-its-750-series-ssd</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>"Intel SSD 750 Review". TrustedReviews. Retrieved 2017-07-16. <a href="http://www.trustedreviews.com/intel-ssd-750-review" target="_blank">http://www.trustedreviews.com/intel-ssd-750-review</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>"SSD Form Factor" (PDF). <a href="http://www.ssdformfactor.org/docs/SSD_Form_Factor_Version1_00.pdf" target="_blank">http://www.ssdformfactor.org/docs/SSD_Form_Factor_Version1_00.pdf</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>"Evolving Storage with SFF-TA-1001 (U.3) Universal Drive Bays". StorageReview.com. 6 March 2020. Devices that are U.3-based are required to be backwards-compatible with U.2 hosts. [...] Enables U.2- (SFF-8639 Module) or U.3- (SFF-TA-1001) compliant drives to be used in the same storage architecture. <a href="https://www.storagereview.com/news/evolving-storage-with-sff-ta-1001-u-3-universal-drive-bays" target="_blank">https://www.storagereview.com/news/evolving-storage-with-sff-ta-1001-u-3-universal-drive-bays</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> </ol>