alextheblue :
Gillerer :
Because of various driver discrepancies, the 64-bit versions of XP and Vista were largely considered unreliable - especially for gaming use.
Horseplop. I had a daily driver with WinXP Pro x64 for a long time and it ran every single game I threw at it, flawlessly. Very solid OS, based off Server 2003 x64. Driver support was actually far better than I anticipated - even my Audigy 2 worked well with it, and Creative drivers are notorious for issues (although this was back in their better years perhaps).
WinXP Pro x64 was a rare bird though. No one installed it unless there was a specific need. I know of a GIS (Geoscience) business where there program worked with some seriously large SEGY files and needed a lot more RAM beyond the 4GB limitation inherent with 32bit. The number 1 problem was getting proper printer drivers support. At the time, they were buggy as heck and would often crash the printer spools service. In some cases, BSOD the computer. Though I blame that on the vendor than Microsoft.
TLDR; Windows 7 was the first true "prime time" 64bit OS for the desktop.