For almost two years, AMD's eighth-generation, 64-bit "Hammer" CPU architecture has garnered endless media exposure, while the actual processors have slowly made their way from paper announcements to real-world products. Now the wait can be counted in days, not quarters: While the desktop and notebook-oriented Athlon 64 chip has been scheduled for September 2003, the server and workstation-optimized Opteron will debut less than a month from now, on April 22.

While CPU Planet has already offered an introduction to the Hammer family, it's time for an update of what's known about the Opteron, the systems that'll use it, and the software that'll be available for it.

Opteron Changes Everything

The Opteron is radical -- it represents a totally new CPU architecture, system platform, and even microcode support all rolled into one. The Opteron is conservative -- AMD's x86-64 architecture runs current 32-bit applications, and quickly, while giving forward-thinking buyers a transition path to 64-bit computing rather than the start-from-scratch approach of Intel's 64-bit Itanium family.

The 0.13-micron-process silicon-on-insulator Opteron -- a 90-nanometer-process successor will arrive in 2004 -- features two more pipeline stages than AMD's Athlon XP; instructions-per-clock-cycle boosters such as enhanced branch-prediction algorithms and larger translation look-aside buffers; support for the SSE2 streaming multimedia instructions that debuted in Intel's Pentium 4; and up to 1MB of Level 2 cache, all in a new, plus-sized processor die or 940-pin ceramic package. (The Athlon 64 will use a different, 754-pin socket.)

Both the Opteron and Athlon 64 boast 64-bit data and address paths and break through current 32-bit CPUs' 4GB memory addressing cap with 40-bit physical (up to 1 terabyte) and 48-bit virtual (up to 256 terabytes) memory addressing space. The Opteron also supports three HyperTransport links, providing up to 19.2GB/sec of bandwidth, versus the Athlon 64's single HyperTransport link for 6.4GB/sec of data transfer.

In terms of architectural changes, the most noticeable is the Opteron's integrated memory controller -- a 128-bit, dual-channel design supporting DDR266 and DDR333 SDRAM. Both the Opteron's memory controller and the Athlon 64's -- a single 72-bit channel -- take that job away from its traditional place in the system chipset's external Northbridge, greatly reducing the latency of read/write requests. This essentially controls the system at, or yields a front-side bus speed matching, the clock speed of the CPU.

New Model Numbering

PC processors have traditionally been identified by their clock speeds. AMD's Athlon XP took a step away from literal megahertz to model numbers based on virtual speeds -- the company says the Athlon XP 3000+ offers performance equivalent to an original Athlon design running at 3GHz, while most users compare it to Intel's 3.06GHz Pentium 4.

The Opteron model numbering system moves away from clock speed altogether, rolling the CPU's scalability and performance into one easy-to-digest, three-digit number. The first number represents the number of processors supported for simultaneous or multiprocessing installations; the basic Opteron lines are the 100 Series (single processor), 200 Series (dual processors), and 800 Series (up to eight-way multiprocessing).

The next two digits -- for the first Opterons, numbers in the 40s -- indicate relative performance within (not necessarily across) the series. For example, an Opteron 240 would be the base model for dual-processor server and workstation platforms, while an Opteron 242 would be a faster alternative for the same systems. (Actual model numbers haven't been officially announced, but we think the above is a good guess: Before a hasty, likely-urged-by-AMD switch back to just "100 Series, 200 Series, 800 Series" yesterday, server vendor PSSC Labs' site offered pre-order shoppers a menu of Opteron models 140, 142, 240, 242, 840, and 842 -- Ed.)

This new numbering scheme is definitely a gutsy move, as the obvious questions in buyers' minds will be how much faster the higher-numbered Opterons will be, and at exactly which clock speeds they will run. It seems obvious that Intel will continue to hold the clock-speed advantage (its Xeon currently peaks at 3.06GHz), while AMD might well win the performance race -- it's shown estimated 32-bit benchmark results that show a 2.0GHz Opteron comfortably ahead of the 2.8GHz Xeon.

AMD has already successfully shifted gears with the Athlon XP model numbers, and the server business is far more interested in performance, scalability, and architecture than outright core speed. If in doubt, head on down to your local IT department and ask what's under the server hood; you might be surprised to find many systems with only 250MHz to 500MHz per processor.