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AMD's Socket AM3 Phenom II processors


The Phenom II goes mainstream and adds DDR3 support
— 2:08 PM on February 17, 2009

It seems like only last month, we were reviewing the first Socket AM2+ versions of the Phenom II processor.

Perhaps because, well, we were.

Yet here we are a month later, and AMD has produced a new revision of the Phenom II capable of working with Socket AM3-style motherboards and DDR3 memory. Hard to keep up sometimes, innit?


Fortunately, although the change is no small accomplishment for AMD, it is relatively simple in the grand scheme of things. The Phenom II's memory controller has been modified to add support for DDR3 memory, mainly. Another happy consequence of the new silicon revision is additional clock speed headroom for the "uncore" (as Intel might call it) portions of the Phenom II—the memory controller, L3 cache, and HyperTransport—whose clocks run at 2GHz in this wave of new Socket AM3 processors.

Beyond that, little has changed in a month. The chips are still manufactured using AMD's 45nm SOI fab process, and AMD hasn't even modified its die size or transistor count estimates: they're still 258 mm² and 758 million, just like previous Phenom IIs. The new chips are still compatible with existing 7-series chipsets from AMD, as well.


A Socket AM2+ processor (left) next to a Socket AM3 CPU (right)

The move to a new memory type requires a new pinout configuration, though, and that's where Socket AM3 comes into the picture. You'll need a Socket AM3 motherboard in order to use these Phenom II processors with DDR3 memory. This new socket type looks an awful lot like the prior Socket AM2+, but it has two fewer pins, for a total of 938. As a result, Socket AM2+ processors can't fit into Socket AM3 motherboards. But in a clever muggle trick, Socket AM3 processors will happily drop into Socket AM2+ motherboards and work with DDR2 memory.


Socket AM3 retains the same lever-style ZIF socket as

Socket AM2+ and should be compatible with the same coolers

As you probably know by now, DDR3 memory enables higher clock speeds (and thus bandwidth) than DDR2-type memory, and it can operate at lower voltages, leading to reduced power consumption, as well. As with many such transitions, DDR3 isn't magically better than DDR2 in every way; it's just an incremental improvement. And, although it's been around for a while now in Intel systems, DDR3 still costs more per megabyte than DDR2. Most folks expect shipment volumes to tip in favor of DDR3 at some point this year, though, and when that happens, prices should become more even. Heck, DDR3 is already pretty stinkin' cheap, even if it does cost more than DDR2.

The new Phenom IIs officially support DDR3 memory at up to 1333MHz, but the multipliers are present for 1600MHz operation, as well, as they are in high-end Core 2 and Core i7 systems. Unlike the Core i7, the Phenom II still has "only" two memory channels onboard, not three. I say "only" because each channel of DDR3-1333 memory can transfer up to 10.7 GB/s. Combined with the 2GHz HyperTransport 3 link on each CPU, the total bandwidth available via Socket AM3 is roughly 37.3 GB/s, considerably more than the peak data rate of 10.7 GB/s available via a Core 2 processor's front-side bus (even if it is less than the staggering 64 GB/s possible with a Core i7-965 Extreme and three channels of DDR3 at 1600MHz.) One caveat: the Phenom II only supports 1333MHz DDR3—at least, officially—with a single DIMM in each memory channel. With four DDR3 DIMMs, 1066MHz is the standard. Such limitations are nothing new, of course. Previous Phenoms have long supported 1066MHz DDR2 memory, but only with a single DIMM per channel.


An unnecessarily large close-up of the Phenom II X4 810

Oddly enough, the newest Phenom II chips aren't the fastest ones. The first wave of Socket AM2+ only processors, including the X4 920 and 940, are higher end products with faster core clock speeds. The first Socket AM3 parts are cut-down versions of the Phenom II with lower speeds and less cache. Here's a list of 'em all.

Model Clock speed North bridge/
L3 cache speed
L3 cache
size
Cores TDP Price
Phenom II X3 710 2.6 GHz 2.0 GHz 6MB 3 95W $125
Phenom II X3 720 Black Edition 2.8 GHz 2.0 GHz 6MB 3 95W $145
Phenom II X4 805 2.5 GHz 2.0 GHz 4MB 4 95W -
Phenom II X4 810 2.6 GHz 2.0 GHz 4MB 4 95W $175
Phenom II X4 910 2.6 GHz 2.0 GHz 6MB 4 95W -

I haven't listed it above, but as with all Phenoms, these Socket AM3 processors have 512KB of L2 cache per core. Also, notice that there's no pricing for the Phenom II X4 805 and the X4 910. Both of these processors are only intended for large PC makers, so AMD hasn't set any retail pricing for these products.

We have two of the retail products in hand today. The X4 810 is a quad-core processor with 4MB of L3 cache (the remaining 2MB in silicon has been disabled), and AMD has positioned it roughly opposite the Core 2 Quad Q8200, given its price tag of 175 bucks. Like the Phenom II X4 810, the Q8200 has a 95W TDP rating, so the matchup between these two rivals should be fairly straightforward.

Less so is the case of the Phenom II X3 720, which has a higher clock speed of 2.8GHz, a full 6MB L3 cache—and one core disabled. AMD cites the Core 2 Duo E8400 as the 720's most direct competitor, and that's a bold statement indeed, since the E8400 has been an enthusiast value favorite for some time now. The E8400 has two higher performance cores, against the 720's three lower performance ones. We'll have to see how that dynamic works itself out in the performance sweeps, but the answer is likely to be complicated. Another complication: the E8400 is a 65W part, while the X3 720 has a 95W TDP, so you may pay in added power consumption for the additional core. That downside may be offset by the fact that the X3 720 is a Black Edition processor with an unlocked upper multiplier for dead-simple overclocking. All in all, an intriguing matchup.


Asus' M4A79T Deluxe mobo

The first Socket AM3 motherboard to make it into Damage Labs is the Asus M4A79T Deluxe, pictured above. This is a relatively high-end board based on the 790FX chipset, and it includes a total of 32 PCIe 2.0 lanes for graphics, which can be configured in various ways across its four physical PCIe x16 slots, including dual x16 and quad x8 arrangements. As you can see, this mobo packs the customary complement of high-end features, with more ports than Oakland (and probably a better football team, too.) The M4A79T Deluxe is already listed at a couple of online vendors for around 200 bucks. In my limited use of this board during CPU testing, I found it to be in pretty good shape for such an early product, with exemplary stability during normal use and decent overclocking headroom, as well. We'll see about subjecting it to a full review soon.