New quad core server CPUs: AMD Barcelona vs. Intel Harpertown

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AMD Barcelona

AMD released the specifications of its new quad core processor, codenamed Barcelona, quite a while ago. Now that the product has been released itself, there is little to add to the story, except all the fancy names AMD has given to the new technologies in the CPU. A short recap for those hazy on the details: Barcelona is a quad core processor, which means AMD has placed four cores in one chip. Within the new Opteron processors, each of these cores has 512 kB L2 cache. In addition to that, there is 2 MB l3 cache. The CPU is manufactured on a 65 nm process in AMD's plants in Dresden. It has about 463 million transistors.

The four cores in the Barcelona CPU are easily identifiable.

Aside from a lot of architectural improvements to heighten performance, Barcelona has a lot of tricks up its sleeve to lower power usage. For example, the clock frequency of all four cores can be independently varied (Independent Dynamic Core Technology), the cores and integrated memory controller work where possible at separate voltages that are kept as low as possible (Dual Dynamic Power Management) and inactive parts of the CPU are shut down when they are not needed (CoolCore technology).

Promises

At the introduction in Spain, Barcelona - where else - AMD made no promises that the new product would be the fastest of its kind. As it turns out, concessions had to be made with the clock speeds: while rumours spoke of 2.5 GHz for the new Opterons, the first CPUs to market are no faster than 2.0 GHz. A faster 2.5 GHz model is planned to be released before the year is over though. AMD does, however, intend to deliver the best performance per watt, not just by constraining the energy use of the processor, but also by opting for ordinary DDR2 memory rather than the power guzzling FB-DIMM technology.

Another focal point for AMD is 'investment protection': the new quad core Opteron models should work seamlessly in all existing Socket F servers, with only a BIOS upgrade as a condition for a smooth transition. AMD sees a large market for server upgrades, i.e. companies outfitting their existing dual core Opteron servers with new quad core CPUs. We approached several server manufacturers to ask their opinion on this strategy, but it would appear no one really buys into the idea of end users purchasing separate CPUs. The platform not changing with the new processors does have another positive consequence: it will be relatively easy for server manufacturers to bring a quad core Opteron offering to market, as they can use their existing product lines as a basis.

An important part of the idea of 'investment protection' is that the new Opterons will not only use the same platform, but also have the same demands when it comes to maximum power useage (TDP). With the current dual core Opterons available in varieties that need a maximum of 68, 95 or 120 Watt, exactly the same demands go for the new quad cores. As AMD puts it, you get two more cores without a rise in energy use or temperature.

Because a PC's energy consumption is becoming more and more important, AMD from now on will not speak of TDP values, as these are only of interest to server designers. The new magic abbreviation is ACP, meaning Average Compute Power, and as the name indicates this should tell you how highe the average power consumption is when the CPUs are fully stressed. For the 120 W TDP CPU, AMD figures on an ACP of 105 W. Similarly 95 W TDP will be about 75 W ACP and 68 W TDP come to 55 W ACP.