A Fleet of X3s

The Lineup, Explained

AMD is rolling out three triple-core Phenom X3 processors, nestled in tightly against the price tags of its fastest dual-core models. The Phenom X3 8750 runs at 2.4 GHz, the X3 8650 runs at 2.3 GHz, and the X3 8450 runs at 2.1 GHz.

Notice that the trio belongs to AMD’s 50-series. That is, the last two numbers of each chip’s model designation ends in 50, invoking the B3 silicon revision, which fixes a cache problem plaguing older Phenom processors. We’ve heard AMD representatives make mention of some other tweaks to B3 unsubstantiated by details. Even still, if you buy a Phenom, make sure it’s one of the new 50s.

All three Phenom X3s feature similar specs. That’s 64KB of L2 instruction cache and 64 KB of L1 data cache per core—totaling 384KB of L1 memory on the processor, 512KB of L2 per core totaling 1.5MB, and the same shared 2MB L3 cache you already know from AMD’s Phenom X4 series. We’re told the fourth core is still present, it’s just switched off. And no, AMD says there isn’t any hope of enabling it through a BIOS modification. The lock is hardware-based. Besides, it’d be a shame to sacrifice stability by switching on a likely-faulty fourth core.

The three X3s sports memory controllers similar to what you’d find on a Phenom X4. Running at 1.8 GHz with AMD’s Dual Dynamic Power Management technology, you should see better memory performance and lower power consumption than previous-generation Athlons at the same TDP rating. Use unregistered DIMMS at speeds as high as DDR2-1066 and you’ll be in good shape.

Phenom X3 processors work with the 940-pin AM2+ socket interface, meaning they support HyperTransport 3.0 and the bandwidth benefits conferred. The link runs at 1.8 GHz, yielding an effective 3.6 GHz data rate. Only the Phenom X4 9850 boasts more throughput thanks to its 2 GHz connection. Of course, you can still drop Phenom X3 processors into older AM2 motherboards. They’ll simply run a slower HyperTransport connection and not support Dual Dynamic Power Management.

Power to the Phenoms

Manufactured on AMD’s 65nm SOI node, the Phenom X3 die consists of roughly 450 million transistors occupying 285 square millimeters of silicon real estate. AMD says that one processing core is turned off completely, though. So you’re not actually powering all 450 million transistors—and it wouldn’t be fair to simply subtract one-quarter of them, since the full 2MB L3 repository is still intact.

Nevertheless, the result is a processor that, according to AMD, runs cooler—at comparable clocks—than the Phenom X4. The company’s own specifications show the difference. A Phenom X4 9750 running at 2.4 GHz features a 125W TDP. The Phenom X3 8750 running at the same frequency is rated at 95W. That’s a 30W savings at the cost of one core. It’s worth noting that those savings come from AMD’s ability to run the 2.4 GHz Phenom X3 at a lower nominal voltage than the Phenom X4.

Just to triple-check, we fired up our test bed with both processors and compared numbers. What we found was a closer to 50W difference. Under load, the Phenom X3 machine was eating 300W of power. Meanwhile, the X4-equipped platform was pushing 355W.

While the 95W Phenom X3 family might not be a play on power savings, AMD is indeed shutting off power to that fourth core. Hmm. Perhaps that’ll help our overclocking efforts.