As any supporter of a losing sports franchise knows, it ain’t easy being a superfan. For the last two seasons, AMD loyalists have watched Intel’s Core 2 Duo and Core 2 Quad embarrass the Athlon 64 and QuadFX off the field. Yet devotees have chanted the refrain of the truly faithful: Come next season, baby, watch out!

Well, it’s next season and AMD’s chance to prove that it’s still a contender is finally here. This month, we bench, dissect, and ponder the hell out of AMD’s new CPU to find out if the Phenom lives up to its name.

The Scoop on Phenom

Before we get down to the business of benchmarking, here’s the backstory on AMD’s new CPU.

AMD’s “true quad core” jams all four cores onto a single 65nm, 285mm2 die. In addition to other core-efficiency enhancements, AMD now uses a shared 2MB L3 cache that runs at the same speed as the memory controller, which is currently 1.8GHz or 2GHz.

Q: How do you pronounce Phenom?

A: It’s fee-nom, not fuh-nom.

Q: What advances does Phenom offer?

A: Phenom is AMD’s first quad-core processor and is touted as a “true quad core.” Based on a 65nm process, Phenom uses an enhanced version of the stellar K8 Athlon 64 core, which features many of the same “wider and faster” techniques as Intel’s Core 2 Duo. Improvements over the Athlon 64 include the ability to execute SSE instructions in 128-bit chunks versus 64-bit. Cache speed gets a bump, as well, with L1 going from 16 bytes per cycle to 32 bytes per cycle, and L2 going from 64 bits per cycle to 128 bits. AMD also spends silicon on increased floating-point performance; a few new instructions; HyperTransport 3, which nearly quadruples the bandwidth over previous implementations; and more L3 cache.

Q: What’s meant by “true quad core”?

A: Each Phenom features four execution cores on one single, contiguous die. Architecturally, it’s far more elegant than Intel’s quad core, which fuses two dual-core chips in a CPU and forces the dual-core islands to talk to each other over the front-side bus. Phenom was designed from the get-go as a quad chip, and each core communicates at HyperTransport 3 speeds—several orders of magnitude faster than Intel’s front-side bus. All the cores can also share data stored in the L3 cache, so a core would have to reach out only to the L3 instead of the much slower system RAM in certain applications. This adds up to a chip that, on paper, seems to at least equal—if not exceed—Intel’s Core microarchitecture.

Q: What clock speeds will Phenom come in?

A: Just two speed grades will initially be available: a 2.2GHz Phenom 9500 and a 2.3GHz Phenom 9600. In a few months, two additional speeds will be offered: a 2.4GHz Phenom 9700 and a 2.6GHz Phenom 9900. While all feature the same microarchitecture and cache amounts, there are key differences. The 9500 and 9600 are much cooler at 95 watts apiece. The 9700 increases to 125 watts and the 9900 hits a Prescott-like heat dissipation of 140 watts. You do get something in return, however. The 9900 will run its HyperTransport link at 4GHz compared to 3.6GHz in the lower-clocked parts, and its memory controller runs a bit faster at 2GHz versus 1.8GHz in the others.

Q: Why are only two of the four CPUs available now?

A: AMD’s true quad-core approach sounds great on paper but it’s also directly responsible for delays in getting the chip out and hitting higher clock speeds. We’ll remind you of the four-leaf clover analogy: While Intel makes its four-leaf clovers by fusing a pair of two-leaf clovers, AMD grows all-natural four-leaf clovers. Unfortunately, the latter are much harder to come by. AMD has admitted that problems at the fab are the reason for the late launch of Barcelona—the Opteron quad core—and with Phenom. And of the CPUs that AMD is able to produce, not enough reach 2.4GHz or 2.6GHz to launch the chips right now—thus the initial 2.2GHz and 2.3GHz CPU rollout.

More Answers on Page 2!

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amd, cpu, processor, Review, AM2, hardware, Phenom, 45nm, 65nm

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