Posted: June 5th, 2001
Written by: Tuan "Solace" Nguyen

AMD 760MP Power

Enter interstate 760, the first true Athlon multiprocessor architecture. Poised to take the workstation and server market by storm, the 760MP chipset is the first of its kind. The AMD 760MP chipset expands on the standard features that are available on the 760 chipset.

Socket A Athlon above 1.2GHz support, 200 and 266MHz FSB support,
PC2100/1600 DDR SDRAM support,

But so what right? Other chipsets support the above chipsets too. So what exactly does the 760MP offer above the 760 besides dual processor support? Transaction Concurrency!

Concurrency means at the same time, and both processors will be able to access the memory bus at 266MHz. On traditional multiprocessing platforms from Intel, CPUs share the data bus and thus latency occurs and speed slow downs. While both CPUs access the memory pipeline at the same time on the AMD side, each CPU gets its own direct bus. This is already a known fact when AMD first released its Athlon processor.

This simultaneous memory data access is achieved through what is called the Point-to-Point bus. Simply stated, PTP Bus allows both Athlon MP chips to have their own separate bus. We can already see the performance benefits from this technique. This benefit however, doesn’t come without a price. Letting each processor have its own physical bus, requires that the northbridge be outfitted with more connections. The northbridge will need more connections to the motherboard and manufacturing becomes more complex and difficult. The 760MP northbridge is the most complex chipset AMD has ever had to manufacture with 1000 micro connection balls (ball grid array).

Once AMD revs up the front-side bus to 400MHz, each CPU will have access to information at any time it needs at the rate of 2.1GB/sec, each. If you’re using two CPUs, guess how much speed you’ll have in total? That’s right. However, that’s the peak speed and since the split load between processors will never be truly halved, that peak rate will never be achieved. On the Intel front, the comparing processor platform will be the Xeon platform. The Xeon technically has a faster bus speed than the Athlon MP and it’s running at 3.2GB/sec but as you add more Xeon processors, they will share the same pipeline. Each Athlon MP will have its own physically independent pipeline bus. So does this mean we’ll be seeing double the performance in memory intensive applications? Not so. Why? Because when it all comes down to it, everything still has to pass through the single 64bit DDR memory pipeline. All the lightning fast execution occurs internally but still must pass through a much slower external memory bus. Now, if there comes a dual channel or even four channel DDR memory solution, then PC2100 DDR modules will definitely play a pivotal roll in increasing the Athlon MP’s performance significantly.

The saying "a chain is only as strong as its weakest link" holds true here for 760MP. While the processor and memory subsystem is blazing along at more than 2.1GB/sec, the traditional PCI bus is still limited to only 133MB/sec peak. To soften the performance hit, AMD has implemented a different PCI controller in the 760MP chipset. The original 760 chipset for the desktop market had a PCI controller that was only capable of 33MHz/32bit/133MB/sec operation. The 760MP brings along a new controller that is capable of the above mode and also 33MHz/64bit/266MB/sec operation. We’ll be seeing a faster 66MHz/64bit controller making its appearance in AMD’s upcoming 76xMPX chipset that Asus will be putting more focus on.

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