Nearly everyone knows that, there's Windows ME, Windows XP Home, Windows XP Pro, Windows XP Corporate and Windows 2003 and you can also buy a Macintosh.
I see you get my point then.
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But I must add - a signifigant portion of computer users dont even know that there are different version of Windows. All they know is that it runs "Windows". If I called 20 people here are work and asked them what version of Windows they were running (pretty much everyone runs XP), probbaly 15 of them wouldnt have a clue. When I someetimes do side work, and I ask people what version of Windows they are running, almost invariably, they cant tell me because they have no clue.