AMD Athlon 64 FX62 Socket AM2 review

It could be a case of the Emperor's new clothes but the AM2 socket for Athlon 64 isn't just about a change of underwear, it's about DDR2.

You have to admire the size of AMD's kahunas. When it launched the original Athlon 64, it took flak for not supporting DDR2 in its new, integrated memory controller. Traditionally - and on modern Pentium chipsets - motherboards used an extra chip, known as the Northbridge, to manage traffic between the CPU and the memory, the whole governed by the speed of the Front Side Bus.

AMD stuck this interface on the CPU die and replaced the FSB with its proprietary Hypertransport interface; one less bridge chip means lower latencies across the board, with the downside that there's less flexibility in the design to use new technologies, like DDR2.

As history has proved, sticking with DDR1-400 hasn't hurt AMD's performance in the slightest; particularly when it comes to games.

Upper hand

Athlon 64s have pounded Pentium 4s into the ground for some years now, partly due to the more efficient processor design, but also because DDR2 memory simply hasn't delivered on its promises of greater speed thanks to a trade off with higher latencies.

Or that was the case until now. With new 800MHz and 1066MHz modules appearing, the price: performance ratio is starting to shift in favour of DDR2 - largely thanks to investments made by Intel. And for this, AMD shows its thanks by beating its rival to a DDR2-800 capable platform.

The problem is that to introduce a whole new memory technology, AMD has to overhaul its entire processor line with a fresh integrated memory controller - and naturally PCF was the first to receive a sample of these new chips, the top of the range dual core FX62.

Each time AMD has fiddled with the memory controller it has updated the socket to make sure confused consumers don't go and try to force a poor defenceless processor into a socket it's not suppose to mate with.

Pin spike

The move from single channel controllers dual saw the pin counts rise from 745 to 939, and for the new socket - dubbed AM2 - AMD has added one extra pin (purely to differentiate them, we believe).

AM2 is more than just about DDR2 but by far this is the key reason for anyone jumping onboard. The beauty of not being tied to an FSB, for example, means that AMD chips should run the newer 1,066MHz specced DDR2 memory at full speed regardless of the motherboard - unlike Intel chips which are limited to a top speed by their FSB.

At launch AMD will have a complete range of AM2 compatible processors and thanks to HyperTransport, all the existing chipsets are automatically compatible: they just have to be integrated to a DDR2 ready motherboard, another advantage of the integrated memory controller. But how does the new range perform?

It could have stayed with DDR1, of course, but AMD's biggest problem right now is Intel's Core Duo revision, Conroe (see PCF187 and the Core Blimey boxout), due very soon.

While it still has the chance, AMD is going to make sure it clings onto the performance crown with the release of the mighty FX62. At the most basic level, it's a simple bump in clock speed over the FX60, jumping from 2.6GHz to 2.8GHz.

It is of course dual-core, still has the twin 1MB L2 cache and the same L1 cache. Without that new memory controller, in fact, there's not a lot new here at all.

As you'd expect for a $1,000 chip, though, it beats everything on sale so far in the benchmark stakes. Our test system comprised of the FX62, 1GB of DDR2-800 memory and an ATI Radeon 1900XTX.

For overall system performance a Sysmark 2004 score of 297 came tantalisingly close to being the first score over 300 we've seen, while 3DMark 06 hit 6,044 and 3DMark 05 11,902. Doom 3, at the standard High Detail settings, scored a whopping 159.1 FPS when we fired it up.

Media encoding

With Blu-ray and HD-DVD just around the corner, media encoding is ever more important and the FX62 proves to be a power-house finishing our Windows Media Encoder test in two minutes dead while 1080p playback showed an average CPU use of just 19% and a peak of 40%, see Conroe crunchtime)

Some of the results tell a less exciting story, mind. The running temperature of the FX62 is phenomenally hot. At 86OC this 125 watt CPU is one of the hottest processors we've seen and shows that to go further AMD has to move to its new 65nm process - though the rest of the AM2 range is at a more reasonable 85W, 65W or even 35W (for the mobile versions).

Memory results do show that the FX62 integrated memory controller and DDR2-800 (CL4) combination is a phenomenally fast partnership.

The Sandra 05 test scored the DDR2-800 bandwidth at 7,110MB/s, faster than anything we've seen from Intel. Compare this to 5,573MB/s for an Athlon 64 4800 running DDR1-400, and it's a more than 27 percent increase. An Intel Extreme Edition hits around 6,700MB/s with DDR2-800, so the FX62 memory implementation is certainly faster.

We also underclocked the FX62 to 2.4GHz, the same speed as the current Athlon 4800 running DDR1-400, in to see how big an effect DDR2 really has on overall system speed.

The DDR2 chip outperforms the 4800 , but only just. Our underclocked FX62 scored 268 in Sysmark, 2:16 in WME and 146 FPS in Doom 3, compared respectively to 266, 2:24 and 140 for the 4800 . So at best the DDR2 memory is offering a six percent increase in speed. Hardly an aweinspiring figure, and it goes to prove AMD was right to hold off on DDR2

While a socket change is enough to turn your motherboard upside-down, AMD also wants to pull the rug from under you and fiddle with the retention mechanism. That's the bracket that holds the CPU cooler.

Apparently two screws simply isn't enough, and the new bracket, while having the same dimensions, has four screws. That's just down to these things breaking on occasion leaving a heavy CPU cooler to float around inside a PC.

The other change reduces the mounting "lugs" at either end of the bracket from three to one. As the bracket is the same physical size for the majority of coolers there shouldn't be a problem and in fact our standard Socket 939 cooler attached perfectly.

Multiple OS

With AM2 processors, AMD is also taking the opportunity to implement its Pacifica Virtalization. This is a technology that greatly speeds up running multiple virtual operating systems and does a similar job to the Intel technology, but of course is incompatible with it.

The main market for this is at the server and business end, but even at home it should help accelerate running legacy operating systems (such as XP on Vista?) when we need them.

Virtualization is also a key part of AMD's Live! initiative: in the AMD accelerated home, one PC sits upstairs in the office and streams media to slave devices all over the house.

With enough CPU cores and virtual OSs, it should be possible to use the same box to surf the net, play games and decode H.264 - or at least that's the argument. We're fairly sceptical about it all at this stage, but right now it's a little hard to test.

If AM2 has piqued your interest expect to find two types of models available at launch. AMD is categorising them into two power envelopes running either at 65 watts or 35 watts, with the FX sitting in its very own hot tub at 125 watts.

While these ratings don't affect functionality, they do help people choose the right type of CPU, so if you want a quieter, cooler processor opt for a 35 watt unit. The jump to AM2 was inevitable and just like the initial shift to DDR1 doesn't provided a great leap in speed, even with DDR2 reaching the heights of 1,066MHz.

In a couple of years we'll have DDR3, which may improve things. But for now, there's no doubt the FX62 is the fastest desktop processor out there on the shelves at the moment, but with the shadow of Conroe looming on the horizon, AMD's grip on its performance crown is definitely slipping. Neil Mohr