InfoWorld: If you think AMD’s Opteron and Intel’s Nocona -- or more formally, “Xeon Processor with 800MHz System Bus” -- are cut from the same 64-bit cloth, look closer. Yes, they’re compatible at the instruction-set and register levels; they should be because they’re both based on AMD’s x86-64 specification. But the total system architecture surrounding these chips -- which includes pathways to other CPUs, memory, and peripherals -- exhibits several differences that factor into buying decisions and developers’ platform targeting.

At its core, Nocona is a NetBurst Xeon DP, a Pentium 4 equipped for dual-processor operation. It has 1MB of Level 2 cache and a top clock speed of 3.6GHz. All memory and I/O data, interrupts, interprocessor communication, and address requests flow over a fast shared bus with a maximum bandwidth of 6.4GBps. It’s a highly evolved design, on the leading edge while remaining faithful to the legacy design principles that Intel is expected to maintain.

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