I have XP Pro on most of my pc's but I have my super pc as I call it that runs XP Pro x 64 and it is a different animal. this pc is a 690 dell precision with dual xeon 5355 quadcore on a 1 kilowatt chassis and 16 gig ram and 4 750 GB raid 1 hard drives and a 512 mb FX4500 graphics card and sound blaster extreme sound car. What use to take minutes takes about 6 seconds or less on it. It is for work only. The memory is on riser cards which was new to me and it can expand to 64 GB ram. I mainly bought it because I got tired of my other pc's really not being work pc's. I was using a gamer gen 4 dell with 4 gig ram and it is an awesome gaming pc but I sure can tell the difference.

 

So was XP until Service Pack 1