Analysis: AMD dual core technology

AMD ships desktop dual core Athlon 64

Although it comes the month after Intel managed to bring us its first dual-core processor, AMD is keen to point out that it was the first manufacturer to demonstrate a working dual-core processor design in August 2004. And it is true that until Intel pulled off the incredible recent acceleration in its product plans, it looked like AMD was going to get there first. But although the new desktop dual-core processor, dubbed the Athlon 64 X2, is behind the Pentium Extreme Edition and Pentium D in terms of release dates, it is significantly ahead when it comes to the performance benefits of dual core over single core: we saw render times almost halve.

But quite aside from speed, the first advantage the X2 has over Intel is compatibility. Where Pentium D processors need new chipsets and VRMs (voltage regulator modules) to cope with increased power consumption, AMD is claiming backwards compatibility with existing Athlon 64 90nm-ready motherboards, with only a BIOS update required. We were sent an Asus A8N-SLI Deluxe board for testing, pre-flashed with a beta dual-core-compatible BIOS; it behaved well despite the pre-production firmware. Check AMD’s website for a motherboard compatibility list.

Although dubbed the X2, the new range extends the existing convention when it comes to model numbers. The current fastest single-core part is the 4000+, and the X2 range picks up from there with the 4200+, 4400+, 4600+ and top-end 4800+.

The basic architecture and specification per core of the X2 are essentially identical to existing Athlon 64 designs. The difference is that the new parts – each sporting just over 233 million transistors – are fabricated on a 90nm process, currently only in AMD’s Dresden fabrication facility. The specification of the four new processors breaks down in a similar manner to those of the 3500+, 3700+, 3800+ and 4000+, with varying levels of cache and clock speed. The 4200+ and 4400+ both run at 2.2GHz, with the 4400+ sporting 1MB of Level 2 cache per core to the 512KB of the 4200+. The 4600+ and 4800+ run at 2.4GHz, with the same Level 2 cache differential between them.

The eagle-eyed will have spotted that this means the 4800+ is essentially two 4000+ processors in one. This is distinct from the situation with dual-core Pentiums, where the cores are clocked lower to cope with thermal problems; the Extreme Edition and Pentium D run at 3.2GHz per core compared to the 3.8GHz of the single-core Pentium 4 660. AMD has managed to keep the power within the current design envelope for Athlon 64 boards by reducing the voltage per core slightly from 1.50V to 1.35V. Power consumption is still higher then before, though, up 21W to 110W maximum. Cool’n’Quiet technology is still there to reduce power consumption when the system is idle, although it wasn’t working in our beta BIOS.

The clock speed equivalence is a definite win for AMD, since unlike Intel’s dual-core parts a 4800+ should perform at least as well as the fastest single-core part for single-threaded applications. And that was borne out in our testing: directly substituting a 4000+ for the X2 4800+ yielded results that were never better than the dual-core part, even in single-threaded applications where the second core has little effect besides taking the light load of background system services. Our test setup yielded a real-world application benchmark score of 2.56 for the X2, against a marginally slower 2.50 for the single-core Athlon 64 4000+. Looking at individual scores of the nine applications in our benchmarks test, seven are slightly faster, but not to the extent you would expect from highly threaded applications.