at first the FX and Athlon 64 came different, as FX had 128-BIT memory controllers on 940-pins versions and Athlon had 64-BIT MCT on 754-pin versions.
now both are same, exactlly same just FX-55 have 200Mhz advantage in their newest model, whilst 4000+ Athlon 64 is running at 2.4GHz.
but still FX series didnt came in 90 Micron wafer technology, but Athlon 64 did. and as well both are now on 939-pins making them 128-BIT memory controller integrated.
Also, at first, Athlon 64 came with L2 with 512, which still are coming with same but it depends on naming conventions, as AMD have named their processors according to the current intel processors (like AMD 3000+ will be as equal to 3.0Ghz intel p-4).
therefore AMD Athlon 3700+ 3800+ and 4000+ are though all on same clock @ 2.4Ghz but have difference in their pins and L2 configurations:
Like Athlon 3700+ = 2.4Ghz L2 = 1MB, and on 754 pins (so on 64-BIT MCT) thus considered equalivent to 3.7Ghz Intel
Athlon 64 3800+ is again 2.4Ghz, but on L2 = 512K and 939 pins makes ir with MCT = 128-BIT, so even @ half L2 cache as compared to 3700+, still has 128-BIT MCT, therefore considered equal to 3.8Ghz P-4
whilst 4000+ is 2.4Ghz, 939-pins and 1MB L-2 (200Mhz lower than FX-55, else every thing same)
and 90nm (didnt still showed up in FX series) is amazingly running coole than 130nm (unlike in Intel, 90nm is hotter)
it is generally said that 15-20W low heat is dissapated by 90nm Athlons.
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