There is no 'FSB' in the classical sense on AMD 8th-Generation platforms anymore...see here
' ">http://forums.amd.com/index.php?showtopic=55881 for a detailed explanation.
Assuming that your question is referring to the correct clockspeed for the Hypertransport-link on 939-pin Athlon 64 3700+, then the answer will be 1000MHz
Set you HT-multiplier (could be called 'LDT-multiplier', 'LDT-clock', 'HT-clock', etc. in BIOS) to x5.0
to get the appropriate 1000MHz clockspeed (or just set it to 1000MHz if your BIOS lets you select clockspeeds instead of multipliers).
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AMD Athlon 64 X2 6000+ 89W :: Asus M2N32SLI Deluxe :: 2x1024MB Muskin XP2-6400 DDR2-800 :: BeQuiet! Darkpower Pro 530W :: 2x WD Raptor 74GB/10k rpm, RAID 0 :: ATI Radeon X1950XTX