Unless you count a PC, zero. I have owned, at some point in my life, the following systems:
1) Atari 2600
2) Nintendo Entertainment System
3) Sega Genesis
4) Sega CD
5) Super Nintendo Entertainment System
6) Nintendo 64
7) Playstation 1
I skipped last generation entirely, focusing largely on the PC platform. I may (or may not) buy a Wii and Xbox360.
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