Solaris is a computer operating system, the proprietary Unix variant developed by Sun Microsystems. Early versions, based on BSD UNIX, were called SunOS. The shift to a System V code base in SunOS 5 was marked by changing the name to Solaris 2. Earlier versions were retroactively named Solaris 1.x. After version 2.6, Sun dropped the "2." from the name. Solaris consists of the SunOS UNIX base operating system plus a graphical user environment. Solaris is written in a platform-independent manner and is available for SPARC and x86 processors (including x86_64). Starting from version 10, the Solaris licence changed and the product was distributed free of charge for any system or purpose, but after the acquisition of Sun Microsystems by Oracle in 2009, the product is once again proprietary with a restrictive licence.