Same old Athlon 64/X2

With the move from DDR400 to DDR2, AMD’s taken the opportunity to also introduce a new processor socket, Socket AM2.

AM2 Athlon 64 X2 5000 (left) and X2 4200 (right)

A closer shot of the 5000+

Underside of the CPUs. X2 5000+ (left) and X2 4200 (right).

Physically Socket AM2 looks practically identical to Socket 939. Unlike Intel, AMD continues to mount the processor’s pins to underside of the CPU rather than on the motherboard, while the AM2 socket itself only has one additional pin over the Socket 939 interface it replaces for a grand total of 940 pins. A layman would probably be hard-pressed to see any differences between Socket 939 and Socket AM2 at first glance.

This keeps things simple on AMD’s infrastructure. Motherboard manufacturers won’t have to go back and make sweeping changes to their existing tools used to fabricate the boards, in fact, since both ATI and NVIDIA’s Xpress 3200 and nForce4 chipset are compatible with Socket AM2, all motherboard manufacturers have to do is swap out the CPU socket and memory on their current motherboards to support Socket AM2. Indeed, this is exactly the strategy both ATI and NVIDIA have in place for their integrated offerings; no changes in that space are going to be made in the immediate future.

While the new socket looks similar to Socket 939, AMD has made one key change that should affect the do-it-yourself (DIY) market. The heatsink tray has been redesigned to provide better stability. This means that those of you with Athlon 64/FX or X2 processors may be able to get by with your existing heatsink/fan unit, or at most, you may just need to swap out your heatsink’s Socket 939 clip with an AM2-compatible clip. Zalman for instance has already adapted their popular CNPS9500 cooler for use with AM2; it shouldn’t be hard for other cooler manufacturers to do the same.

Architecture changes

With the debut of the new Socket AM2 platform, many AMD enthusiasts were hoping AMD would use the opportunity to integrate new architectural enhancements designed to improve performance, particularly with Intel’s upcoming Conroe processor right around the corner. AMD saw things differently however.

In order to ease the transition into the new AM2 platform, AMD wanted to keep things simple, there are no significant changes to the processor’s core architecture, at least when it comes to enhancing performance. A Socket AM2 Athlon 64 4800+ features the same cache configuration and clock speeds as a Socket 939 Athlon 64 4800+ CPU would. In other words, it runs at the same 2.4GHz with 1MB L2 cache per core and 128K of L1 cache. The HyperTransport interface is the same on both processors, running at 1GHz DDR, shuttling along up to 8GB/sec of peak bandwidth.

The key difference between both processors is that the AM2 Athlon 64 X2 4800+ boasts up to 20.8GB/sec of total system bandwidth (8GB/sec HyperTransport link + 12.8GB/sec memory) whereas the Socket 939 Athlon 64 X2 4800 tops out at 14.8GB/sec (8GB/sec HyperTransport link + 6.4GB/sec memory), nearly a 30% increase.

By keeping the basic configuration between both processors similar, the model numbers AMD has previously established carry over to their AM2 processors. This is important, as AMD is introducing a top-to-bottom lineup of AM2 processors including the Sempron line, Athlon 64 (single-core), Athlon 64 X2, and Athlon 64 FX lines of processors.

While the core architecture of AM2 carries over basically unchanged, that doesn’t mean that AMD hasn’t incorporated improvements into AM2 however…