Verdict: AMD finally reaches 65NM.
Ever since Intel launched its Core architecture-based CPUs, AMD chips have looked lacklustre. Initiatives that raised the hopes of the company's fans have been, at best, underwhelming and at worst, White Elephants, such as the FX-74. The latest hope for fans is AMD's transition from a 90nm manufacturing process to 65nm.
Intel moved to 65nm last year, and has already spoken about plans to progress to 45nm later this year. Not that we should rubbish AMD's move to 65nm just because it's taken longer; Intel is much richer than AMD, and making CPUs is hugely expensive.
Generally, the smaller the process, the cooler and faster the chip. A smaller manufacturing process means the die is physically smaller. As there's less distance for signals to travel, and the divisions between paths inside the CPU become more minute, less voltage is required. This results in less waste heat, and so should allow the dies to run at a higher frequency. Additionally, their reduced size means there are more dies on each wafer, resulting in higher yields and lower manufacturing costs.
AMD isn't premiering a brand-new architecture with its move to 65nm. For the time being, it's revamping a range of Athlon 64 X2s, and referring to these new Brisbane core models as Energy Efficient chips. They're still Socket AM2 chips and, thanks to their large heatspreaders, they look identical to their 90nm counterparts.
AMD is launching a whole series of 65nm CPUs, but the chip we saw was an Athlon 64 X2 5000+ EE. Like the 90nm version, the 65nm X2 5000+ EE has two cores clocked at 2.6GHz, with a HTT speed of 200MHz and a multiplier of 13. Each core has 128KB of Level 1 cache and 512KB of Level 2 cache. The vcore of 65nm chips should be lower than their 90nm equivalent, and our test chip ran at 1.34V, compared to 1.37V for the 90nm version. As a result, the TDP has plummeted from 89W to 65W.
Although Socket AM2 Athlon 64 X2s support 800MHz PC2-6400 DDR2, not every chip can run this memory at full speed. Memory speed is derived from a combination of factors, including the CPU frequency, multiplier and memory divider. Chips with odd-numbered multipliers can't run PC2-6400 memory at 800MHz (without overclocking), and in the case of the X2 5000+, which has a 13x multiplier, the memory runs at 742MHz.
For testing, we pitted a Windsor core 90nm Athlon 64 X2 5000+ and the new Brisbane core 65nm chip against each other. We needed to flash the BIOS of our Asus Crosshair motherboard for it to recognise the newer CPU but otherwise, installation of the 65nm CPU was identical to that of a 90nm model.
At stock speeds, surprisingly, the 90nm chip was noticeably quicker than the 65nm chip. The difference in DVD encoding was minor, but in our image editing test, and in particular, the multitasking test, the 65nm chip lagged behind the 90nm model. AMD has explained why: the Level 2 cache latency of 65nm chips is higher than that of 90nm chips. According to AMD, this is to allow for larger caches in the future, although it isn't much good at the moment.
While the 65nm chip was slower, it used noticeably less power. With it installed, our test rig - the Crosshair with 2GB of RAM, a GeForce 7900 GTX, and a single hard disk and optical drive - drew 182W from the wall when running two instances of Prime95. With the 90nm chip, this same rig sucked down 204W. Under load, the temperature of the 65nm chip was much lower too; with an Arctic Cooling Freezer 64 Pro fitted, the 65nm chip ran 19ûC cooler than the 90nm version.
Did this make for better overclocking then? Not by much. The 90nm chip was stable with a 220MHz HTT. While the 65nm chip's lower TDP meant that we could whack up the voltage to much higher levels, no matter how much juice it was given, it wasn't stable with anything higher than a 225MHz HTT.
CONCLUSION
AMD's 65nm CPUs consume less power and run cooler than their predecessors, but these were never particular problems for the Athlon 64 X2. Performance against the Core 2 Duo is the issue, and the move to 65nm doesn't improve this. Our 65nm chip overclocked virtually identically to its 90nm counterpart, which is disappointing, especially since the 65nm chip's higher cache latency means there's a performance hit as well. AMD needs its next-generation native quad-core Barcelona core CPU. Soon.
