Solaris is the Unix file system released by Sun Microsystems, and designed to supplant previous versions of Unix’s SunOS. Despite that fact, however, the core of Solaris is formed of the current SunOS, which was rebranded as Solaris in 1993 to acknowledge the fact that this new operating system encompassed Open Network Computing functionality and the OpenWindows Graphical User Interface desktop environment, in addition to SunOS. Solaris also differs from SunOS in that while early versions of SunOS were based on BSD (Berkeley Software Distribution), Solaris is based on Unix System V Release 4, which added some key features that the original BSD-based SunOS lacked.
SunOS and BSD versus Solaris and SVR4
BSD has provided the groundwork for several major open-source operating system developments, and continues to do so today. SVR4, however, introduced several key features that helped distinguish Solaris from earlier releases of SunOS. Some of the differences between SunOS and Solaris were purely internal, including a new virtual memory support system, while others helped improve usability, like the OpenWindows GUI, and improved multi-national language support. So, while SunOS continues to form the core of current versions of Solaris (including Solaris 10), Solaris provides some increased functionality above and beyond that provided by SunOS.
While Solaris was originally a proprietary operating system, it now functions as a combination of closed and open-source software. OpenSolaris, an open-source project, was created in 2005 from the then-current development code base, and continues to be able to be downloaded without cost. Sun Microsystems has since indicated that future released versions of Solaris will now be derived from OpenSolaris, making modern versions of the operating system closed and open-source combined.