AMD Socket AM2

In May 2006, AMD unveiled Socket AM2, the fourth generation of its Hammer architecture (which had made its market debut in 2003), and successor to the earlier Socket 754, 939 and 940 implementations. At the same time the company announced that it was transitioning its entire line-up of AMD Athlon 64 X2 dual-core processors over to the new platform, in addition to introducing new AMD Athlon 64 X2 5000+ and 4000+ series dual-core CPUs.

Although Socket AM2 has 940 pins, it is incompatible with the previous generation Socket 940 and Socket 939 connectors. Indeed, this is so both electrically and physically, the pin-out of the new Socket AM2 processors having been changed so that the new CPUs will simply not fit into the old sockets.

The new platform’s major area of innovation is in Socket AM2 processors’ memory controller.

The integration of the system memory controller hub (MCH) into the processor itself, obviating the need for motherboards to have a separate Northbridge chip has been the most important differentiating architectural feature of AMD CPUs since the inception of its family of Hammer processors. Until now this has used DDR memory technology. By 2006, this had become a little outdated, and the new Socket AM2 processors address this issue by having an integrated DDR2 memory controller that operates at specified speeds of DDR2-667 and DDR2-800.

The integration of memory controller and CPU, together with the fact that chipsets are connected to the K8 microarchitecture through a HyperTransport bus, mean that the transition of Athlon 64 processor family to the new socket interface and new DDR2 SDRAM doesn’t necessitate a new chipset. Consequently, all the chipsets that have hitherto been used in Socket 939 motherboards could be used in new Socket AM2 mainboards.

Alongside DDR2 support, the new Socket AM2 processors add support for AMD’s Pacifica Virtualisation technology, designed to enable users to run multiple operating systems and applications in separate partitions on a single processor. Such technology has been commonplace in mainframe and Unix systems for many years, but has always been cumbersome to implement within an x86 architecture. AMD’s Pacifica Virtualisation extensions to the x86 architecture is similar to, but not directly compatible with, Intel’s virtualisation extension for 32-bit and 64-bit x86 architectures. Previously known by the codename Vanderpool, this is now more commonly referred to simply as VT.

The new processor line-up is nothing dramatic in terms of core performance, the FX-62 chip – targeted at gamers and technophiles – clocking in at 2.8GHz, with the top-of-range mainstream 5000+ part not far behind at 2.6GHz. It is a different story though when it comes to power consumption, with all mainstream X2 processors boasting a lower maximum power specification of 89 watts, down from previous models’ 110 watts. More impressive still is the line of Energy Efficient Socket AM2 CPUs, being offered at a small price premium over the regular model versions. These will be available with wattage specifications of 65 watts and, for some models, as low as 35 watts:

The following table summarises the range of processors unveiled in the spring of 2006:

• AMD K6
• AMD K6-2
• AMD 3DNow
• AMD K6-3
• AMD Athlon
• AMD 750 Chipset
• AMD Thunderbird
• AMD Duron
• AMD Palomino
• AMD Morgan
• AMD Thoroughbred
• AMD Barton
• AMD HyperTransport
• AMD Hammer
• AMD Athlon 64
• AMD Sempron
• AMD Athlon 64 X2
• AMD Socket AM2
• Barcelona, AMD’s native Quad Core CPU