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Inside AM3

Socket AM3: AMD's Phenom II Gets DDR3

AMD’s AM3-ready Phenom II processors are very much similar to the existing AM2/AM2+ Phenom II chips.

Each core includes 64 KB of L1 data cache and 64 KB of L1 instruction cache, totaling 512 KB per quad-core processor. Each core also includes 512 KB of L2 cache, adding up to 2 MB per X4 and 1.5 MB per X3 CPU. Then, depending on the model, you get 4 MB or 6 MB of shared L3 cache.

The chip’s memory controller is where you’ll see the real difference between today’s Phenom IIs and the chips launched back during CES. The 128-bit controller remains, interfacing with two 64-bit channels of memory. Whereas the previous Phenom IIs ran their controller at 1.8 GHz, all AM3 processors support up to 2 GHz speeds. AM3 extends memory support to include DDR3-1333 modules in addition to the DDR2-1066 ceiling of the previous generation. Interestingly, if you choose to run DDR3-1333 modules, you’ll be limited to a single DIMM per channel, making your memory purchase particularly critical.

With the increase in memory controller speed comes a faster HyperTransport interface—from 1.8 GHz to 2 GHz as well, upping theoretical bandwidth to 33.1 GB/s from 31.5 GB/s.

That the AM3-able Phenom II, etched on AMD’s 45 nm DSL SOI process, is approximated at 758 million transistors in a 258 square millimeter package makes it clear that these new CPUs employ the same silicon as the existing Phenom II X4 940/920s. The issue, of course, is the socket. With a 940-pin array, there’s no way to shoehorn one of the old AM2/AM2+ processors into the new AM3 socket. Officially, AMD says it’ll update its lineup with faster parts in the near future. But we’re fairly impatient, so we’re going to try to get our AM2+ Phenom II running on the new socket interface today, instead.


The Phenom II goes a long way to improve AMD’s standing against Intel with regard to power consumption. First and foremost, the design enables four p-states, rather than just two. As a result, at idle, the Phenom II chips in our launch review throttled all the way down to 800 MHz. Power consumption dropped in kind, and AMD’s newest design proved itself a much more energy-efficient contender than its predecessor.

At the same time, AMD changed previous power-saving functionality that let each core enter p-states independently. When a thread began on a core running at half-speed, performance naturally suffered. Now, with Phenom II, all four (or three) cores run at the same frequency. But increased granularity in the number of p-states translates into a much better balance between speed and power-savings.

The last Phenom chip in AMD’s armada was the Phenom X4 9950 Black Edition running at 2.6 GHz. That processor was rated at a 140 W TDP, which you’ll remember caused trouble when it was discovered that some inexpensive motherboards weren’t designed to accommodate the increased load and would invariably fail. Shifting to 45 nm immersion lithography helped AMD reign in power consumption with Phenom II and the 3 GHz X4 940 featured a 125 W TDP. All of the AM3-ready chips announced today yield further savings given their 95 W TDPs.

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