Athlon 64 and AMD Opteron 64 have an L1 and L2 cache as follows:
• 64-Kbyte L1 instruction cache and 64-Kbyte L1 data cache
• On-chip L2 cache
You should check out Athlon 64 Software Optimization Guide appendix for details. See page 252 for a block diagram and explaination of how the L1 Instruction Cache works.