The original Athlon chip started being produced in mid-1999. The "original" Athlon architecture consisted of two generations: Classic and Thunderbird (T-Bird for short). Production ended in 2005.
In 2001, AMD released the 3rd generation of the Athlon chips, called as the Athlon XP. "XP" meant to be "extended performance" and also as an unofficial reference to Windows XP.
Logo hasn't been changed a lot; only that they've added the XP text at the bottom.
Athlon 64 (X2)
Athlon 64 is the succesor of the original Athlon chip and the Athlon XP, which competed primarily with Intel's Pentium 4.
AMD announced the newer logos for the Athlon 64 family. Currently, Athlon 64 chips are still produced, but it's glory is now taken over by the Athlon II.
2013 - present
The Athlon II is the sucessor of the Athlon 64 and is aimed at a mid-range budget.
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