One PC, Two Brains

Under the Hood: Dueling Dual-Core CPU Architectures

Our current crop of value desktops contain dual-core processors from AMD and Intel. However, while they share the dual-core moniker, the two companies' desktop CPUs are very different.

From the ground up, AMD designed its Athlon 64 X2 and FX-60 desktop processors to include two cores. Intel created its Pentium Extreme Edition and Pentium D desktop CPUs by putting two single-core chips in one package.

Intel beat AMD to the dual-core desktop punch in April 2005 by assembling the first two-core x86 processor--the Pentium Processor Extreme Edition 840--out of existing parts. Engineers put two 3.2-GHz Pentium 4 cores on the same die (each with its own 1MB Level 2 cache), and then connected them with an external 800-MHz frontside bus.

To boost performance, Intel left in the Pentium 4's hyperthreading technology, which makes the operating system see each chip as two. To create the subsequent, lower-priced Pentium D processor (launched in May 2005), the company employed cores running at slower speeds and turned off the hyperthreading. In January 2006 Intel introduced updated dual-core Pentium D chips based on smaller, faster cores.

AMD rolled out its first dual-core CPUs in April 2005 under the Opteron name for servers and workstations, and then launched its Athlon 64 X2 desktop chip a month later. One of the clearest advantages of AMD's design is the ability of the two cores to communicate with each other within the die so that data doesn't have to travel over a slow external system bus as in Intel's arrangement. Each core gets a 512KB or 1MB L2 cache.

Evaluating the performance of CPUs that use different chip sets is an imperfect science. But in the vast majority of our tests of PCs using comparable processors, AMD's dual-core architecture has proved to be the superior performer.

Both companies have new CPUs on the way. AMD recently launched versions of its X2 and FX processors based on its new AM2 socket, which supports faster DDR2 memory. And Intel is poised to debut its next-generation CPU, called the Core Duo 2, later this year (the first Core Duo was a mobile processor). Based on a new architecture, the desktop Core Duo 2 has exhibited strong performance in early public tests.

Tom Mainelli