The release of IE7 at the end of 2006 resulted in a collapse of IE6 market share; by February 2007, market version share statistics showed IE6 at about 50% and IE7 at 29%. Regardless of the actual market share, the most compatible version (across operating systems) of IE was 5.x, which had Mac OS 9 and Mac OS X, Unix, and most Windows versions available and supported for a short period in the late 1990s (although 4.x had a more unified codebase across versions). By 2007, IE had much narrower OS support, with the latest versions supporting only Windows XP Service Pack 2 and above. Internet Explorer 5.0, 5.5, 6.0, and 7.0 (Experimental) have also been unofficially ported to the Linux operating system from the project IEs4Linux.