As we know Steam OS ranking is different from other data analysis companies because Steam stands for game player's point of view. The latest data report shows that, Windows 7 64 bit is the most popular player system, share of 30.32 percent, that's to say it increases 3.67 percent from last month. Second place is "old" Windows XP 32bit, still 30.17 percent share. And 32-bit Windows 7 is only 11.54 percent of the players favor.
Mac OS also have considerable gains in this list, both version 10.6.3 and version10.5.8 are in the ranking, but the share is much less than Windows.