Comparison of the Microsoft Windows and Linux operating systems is a common topic of discussion among their users. Windows is the most prominent operating system released under a proprietary software license, whereas Linux is the most prominent operating system released under a free software licence. However, most Linux distribution sites also have proprietary components for their distribution available. The two operating systems compete for user-base in the personal computer market as well as the server market, and are used in government offices, schools, business offices, homes, intranet and internet servers, supercomputers, and embedded systems. Windows dominates in the desktop and personal computer markets with about 90% of the desktop market share, and in 2007 accounted for about 66% of all servers sold. In server revenue market share (2007Q4) Windows achieved 36.3% and Linux achieved 12.7%.As of November 2007, Linux powered 85% of the world's most powerful supercomputers. In February 2008, Linux powered five of the ten most reliable internet hosting companies. Linux and Windows differ in philosophy, cost, ease of use, versatility, and stability, with each seeking to improve in their perceived weak areas. Comparisons of the two tend to reflect the origins, historic user base and distribution model of each. Typically, some major areas of perceived weaknesses regularly cited have included the poor out-of-box usability of the Linux desktop for the mass-market and poor system stability for Windows. Both are areas of rapid development in the two camps. Proponents of free software argue that the key strength of Linux is that it respects what they consider to be the users' essential freedoms: the freedom to run it, to study and change it, and to redistribute copies with or without changes.