In October 1999, AMD announced a bold alternative to the proprietary EPIC or Itanium 64-bit processor architecture chosen by Intel: The CPU underdog promised to extend the industry-standard x86 architecture to 64 bits, keeping native compatibility with existing 32-bit software while adding a 64-bit mode for new operating systems and applications to enjoy supercomputing-class memory addressing and performance. The extended architecture would be called x86-64, feature a fast new system bus dubbed Lightning Data Transport, and debut in AMD's eighth-generation processor, codenamed "Hammer."

In April 2003, AMD delivered on its promise, albeit with new nomenclature -- AMD64 for the architecture, HyperTransport for the bus, and Opteron for the series of CPUs that challenge Intel's Itanium family in the high-end server and workstation arenas.

In September, AMD completed its evolutionary shift into a new, yet backwards-compatible, realm of 64-bit computing with the Athlon 64 3200+ and Athlon 64 FX-51 processors for desktop computers. The architecture once reserved for servers is now available for enthusiast and mainstream PCs -- and soon, at least in Athlon 64 guise, for mobile systems.

Significant platform advancement is always welcome news, but also brings some confusion about buying decisions and where new CPUs fit into the market matrix. The three AMD64 processor families share a common lineage, but have notable differences in design, features, and platform support, as well as the usual segmentation in price and performance levels. So let's put the Opteron, Athlon 64, and Athlon 64 FX into context.

Core Design

All of the new AMD processors are built with 0.13-micron silicon-on-insulator (SOI) process technology -- the move to 0.09-micron or 90-nanometer fabrication is expected sometime in 2004 -- and feature 128K of Level 1 and 1MB of Level 2 on-chip cache. (AMD watchers have speculated about Athlon 64s with a smaller 512K L2 cache for the value and mobile market segments, but none have appeared yet.)

Compared to the seventh-generation Athlon and Athlon XP, each member of the Hammer clan features enhancements such as two more pipeline stages, enhanced branch-prediction algorithms, and support for the SSE2 streaming multimedia instructions that debuted in Intel's Pentium 4 -- as well as a memory controller integrated into the CPU instead of located in the Northbridge part of the system chipset.

The Opteron incorporates a robust dual-channel memory controller -- a memory path that's doubled from 64 to 128 bits. It's not technically a true dual-channel design like that of Nvidia's nForce2 chipset, with simultaneous data transfers along two distinct paths, but has the same effect of doubling the data pathways and creating a true 128-bit connection (plus a 16-bit error-correction code or ECC link) to system memory.

Offered in a 940-pin package, the Opteron is available at core speeds ranging from 1.4GHz to 2.0GHz in each of three configurations -- the 100 Series for uniprocessor workstations, 200 Series for 2-way or dual-processor workstations and servers, and 800 Series for 4- or 8-way servers or colossal clusters. Its model numbers indicate series and clock speed, such as the 1.6GHz Opteron 142 and 242 and the 1.8GHz Opteron 844.

The Athlon 64 FX -- the first of which has the model number FX-51; the next-higher-speed successor will be the FX-53, with an FX-55 presumably after that -- is almost a straight transition of the 940-pin Opteron 100 Series to the performance desktop, bringing this high-end architecture to the enthusiast and gaming audience. This announcement was really no surprise, since the Opteron 100 was designed for workstation use, and a few enterprising manufacturers have been offering borderline workstation/gamer Opteron systems for months.

One difference between the Opteron and Athlon 64 FX-51 that pays off in higher performance numbers is a higher clock speed -- 2.2GHz, or a nice 200MHz jump from the fastest Opteron model. The Athlon 64 FX is also limited (on paper, at least) to 1-way configurations, as AMD is looking to keep its desktop and server business separate.