What's the difference between SunOS and Solaris?
SunOS refers to the actual operating system that underlies the Solaris OE (operating environment). SunOS is often used to refer to the old SunOS 4.x, a BSD-like operating system with some SVR4 features and OpenWindows.
Solaris is typically used to refer to SunOS 5.x releases of the operating system and environment from Sun Microsystems. The version of Solaris can be derived from the SunOS 5.x designation by dropping the leading 5. e.g., Solaris 7 is SunOS 5.7. However, some earlier verions of Solaris were numbered as 2.5.1 with a SunOS release of 5.5.1.