On the chip level, AMD engineers added a shared Level 3 cache—an extra pool of memory used to store data close to the processor cores—to help feed data into the cores individual Level 2 caches. The L3 cache, which was designed to vary in size, can be accessed by any of the four cores. However, AMD engineers gave each processor core its own L2 cache on the grounds that sharing those caches can result in one or more processors cores fighting access, which exacts a cost in performance.
The engineers also fitted the quad-core chip design with HyperTransport 3.0, which offers more than double the bandwidth of its predecessor, thus increasing the size of the pipe used to move data into and out of the chip.
While adding these performance-oriented features, AMD engineers also built in some power-saving tricks. For example, cores not being used can be shut down.
While adding these performance-oriented features, AMD engineers also built in some power-saving tricks. For example, cores not being used can be shut down.
AMD will also make provisions for DDR2 SDRAM (double-data-rate synchronous dynamic RAM) and, when the company is satisfied with the technology, FB-DIMMs (fully buffered dual in-line memory modules), which add a buffer chip to enhance performance. At the moment, AMD said, the power use of the FB-DIMMs—each modules buffer chip consumes roughly 6 watts—outweighs their performance advantages.
Ultimately, the effort AMD put into creating the quad-core Opteron will pay off in other areas, as the chip maker will use the design in other chips, Moore said.
"Itll start in the Opteron family and itll trickle down into the rest," he said.
AMD has said it will follow the quad-core chip with a move to a redesigned processor architecture around 2008 or 2009.
Meanwhile, rival chip maker Intel, of Santa Clara, Calif., is also working to deliver quad-core chips in 2007. So far, Intel has shown off a quad-core Xeon, code-named Clovertown.
Following a logical progression, eight-core PC processors may become possible with the next generation of manufacturing technology, 45 nanometers, which Intel said it expects to begin rolling out some time in 2007.
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