AMD Athlon 64 4000+ & FX-55: A Thorough Investigation

It's been a good year for AMD; they've been making money (not as much as Intel, but at least they're in the black) and ask the majority of PC enthusiasts and they're recommending AMD chips. There's obviously good reason; the Athlon 64, while not priced as aggressively as AMD's chips in the past, ends up offering better performance than the Pentium 4, for less money. What more could you want?

Recently AMD made the transition to 90nm with their Athlon 64, but did so on lower clocked parts, much like what Intel used to do whenever they would introduce a new manufacturing process. The first 90nm Athlon 64s came in the flavor of 3000+, 3200+ and 3500+ chips on the desktop, and despite initial overclocking success, 2.2GHz was the highest clock speed AMD introduced at 90nm.

There's no hiding the fact that all chip manufacturers have had some issues moving to 90nm. If they had all of their cards lined up beforehand, the biggest unavoidable issue becomes power density, which you can't simply get around regardless of how mature your 90nm process is. Fighting the incredible power densities of these extremely small cores requires a significant rethinking in how the cores are designed, laid out and even the functional nature of the logic these transistors represent.

Not to be held back by the move to 90nm, AMD continued with the release of two new flagship chips: the Athlon 64 4000+ and the Athlon 64 FX-55. We'll get to the specs momentarily, but needless to say that AMD's approach is in significant contrast to what Intel has recently announced. With the axing of the 4GHz Pentium 4, Intel has effectively let AMD win this latest war of high-cost, low yield CPUs at the very high end. While the victory itself may not mean much come next year or this year for that matter, it is a very interesting change in policy over at Intel. Remember the last time there was a similar push for Intel to ramp up clock speed, the decision was much different, and the market was given a 1.13GHz Pentium III that later had to be recalled. Intel's playing it very safe this time around.

AMD on the other hand has a different strategy. When we published a roadmap calling the Athlon 64 4000+ a 2.6GHz 512KB Socket-939 part back in January, we got a strange email from AMD warning us that the specifications of the Athlon 64 could change. We chalked it up to AMD just doing their usual duty whenever we publish data that is not yet publicly available (or talked about for that matter). But it turns out that their caution was not simply from a PR standpoint; today with an Athlon 64 4000+ in our hands AMD didn't release a 2.6GHz Athlon 64, they just re-released an Athlon 64 FX-53 - a 2.4GHz, 1MB L2 cache part, as a regular Athlon 64 4000+.

CPU manufacturing is all about yields, if AMD can make more chips that work by increasing the die size by adding a larger cache instead of upping the clock speed, then that's the route AMD will take. With the Athlon 64 4000+, it's clear what the outcome of AMD's equations was.

The Athlon 64 FX-55 is however, in line with what we expected. Like the 4000+ and all FX processors before it, the FX-55 features a 1MB L2 cache, but AMD managed to crank the chip up to a full 2.6GHz with the help of some tweaked manufacturing.

The FX-55 uses a type of strained silicon developed with one of AMD's partners, but unfortunately at this point AMD is not releasing much information on their implementation of strained silicon. IBM has been demonstrating strained silicon for years now so it is not too much of a surprise that AMD would have access to this technology for use in their CPUs. Intel first introduced strained silicon to desktop CPUs with their 90nm Prescott chips.

We've already talked about strained silicon in the past, but for a quick refresher here's basically what the technology allows. Silicon atoms found in microprocessors are arranged in a relatively repetitive lattice, with the space in between the atoms allowing electrons and thus electrical current to flow through. The spacing between the atoms creates resistance to the flow of electrons, the greater the spacing, the less the resistance, the greater the flow of electrons. Place a layer of silicon next to a layer of a silicon compound with greater atomic spacing (for example Silicon Germanium), and the pure silicon atoms will end up spacing themselves out more to match up with the SiGe lattice, thus straining the silicon lattice. The end result are freer flowing electrons allowing for faster transistor switching, and in this case higher clock speeds.

The big announcement will be whenever AMD brings strained silicon technology down to their 90nm chips, since 130nm advancements won't mean much going forward. It does appear that AMD's manufacturing partnerships are definitely paying off though, which has helped them address manufacturing as a serious weakness in years past.

So here's what we've got: an Athlon 64 4000+ that is basically a FX-53 (but still clock locked for all higher multipliers like a regular Athlon 64), and an Athlon 64 FX-55 that uses a 130nm strained silicon on insulator process to hit 2.6GHz. Pricing on the two chips is, well, pricey: $827 for the FX-55 and $729 for the FX-53 err we mean Athlon 64 4000+.

Alongside AMD's launch of the FX-55 and 4000+, NVIDIA has announced what may be the chipset to get for the Athlon 64: the long awaited nForce4. For a look at this chipset, which we feature in our review today, read our in-depth look at the nForce4.