The first Technical Preview was first set to expire on April 15, 2015 but Microsoft later released a tool to extend the expiry date, to last until the second tech preview of the OS in May 2015. The second beta version, "Technical Preview 2", was released on May 4, 2015. Third preview version, "Technical Preview 3" was released on August 19, 2015. "Technical Preview 4" was released on November 19, 2015. "Technical Preview 5" was released on April 27, 2016. Windows Server 2016 Insider Preview Build 16237 was released to Windows Insiders on July 13, 2017. Windows Server 2016 was officially released at Microsoft's Ignite Conference on September 26, 2016. Unlike its predecessor, Windows Server 2016 is licensed by the number of CPU cores rather than number of CPU sockets—a change that has similarly been adopted by BizTalk Server 2013 and SQL Server 2014. The new licensing structure that has been adopted by Windows Server 2016 has also moved away from the Windows Server 2012/2012R2 CPU socket licensing model in that now the amount of cores covered under one license is limited. Windows Server 2016 Standard and Datacenter core licensing now covers a minimum of 8 core licenses for each physical processor and a minimum of 16 core licenses for each server. Core licenses are sold in packs of two with Standard Edition providing the familiar rights to run 2 virtualized OS environments. If the server goes over 16 core licenses for a 2 processor server additional licenses will now be required with Windows Server 2016. Windows Server 2016 Technical Preview, released on October 1, 2014, was the first beta version of the operating system made publicly available. Its version number was 6.4.9841. Windows Server 2016 Technical Preview 2 was made available on May 4, 2015. Its version number was 10.0.10074. (A similar jump in the most significant part of the version number from 6 to 10 is seen in Windows 10.) Highlights of this version include:  The third technical preview of Windows Server 2016 was made available on August 19, 2015. Its version number was 10.0.10514. Highlights of this version include:  The fourth technical preview of the operating system was made available on November 19, 2015, one year and one month after the initial technical preview. Its version number was 10.0.10586. Its highlights include:  The last technical preview of Windows Server 2016 was made available on April 27, 2016. Its version number was 10.0.14300. Its highlights include:  Windows Server 2016 was released to manufacturing on September 26, 2016, bearing the version number of 10.0.14393 (same as Windows 10 Anniversary Update).