I can't decide whether it was my dual Celeron 366@550, 256MB of system RAM, Abit motherboard (can't remember the model # now), 16MB TNT video (for DX games), along with SLI'd 12MB Voodoo 2's.
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My first Athlon, a 600 Mhz Thunderbird @ 700 Mhz, on an Asus K7M, 192MB of PC133, and a 32MB TNT2 @ Ultra, and dual 7,200 RPM hard drives.
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My XP-M 2600 @ 2.5 Ghz, with 1GB of Mushkin BH6, a 9800 Pro, on an Epox 8RDA3+PRO.
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My current favorite, my Q6600 @ 3.2 Ghz, a Gigabyte GA-P35C-DS3R, 4GB of G.Skill PC6400, eVGA 8800GT-SC, with 1TB of HD space, including a WD6400AAKS. I'm seriously considering swapping out the motherboard for an Asus P5Q Pro, like I'm using with my E7200, though.