Benchmarks: Intel Core i7 (Nehalem)
Published: 04 Nov 2008
Nehalem features, test setup & power consumption
Intel has also cribbed a few virtualisation ideas from AMD for the Nehalem architecture. With the introduction of the Barcelona processor, AMD offered Rapid Virtualisation Indexing (RVI) to allow virtual machines direct memory access. Virtualisation specialist VMware enthusiastically backed the AMD technology. The equivalent technology in Intel's Nehalem is called Extended Page Table (EPT).
On top of the ideas borrowed from AMD, Nehalem chips offer a number of additional features. For example, the four processor cores can work on two threads at the same time, a refinement of the P4's well-known Hyperthreading architecture. As well as the four physical arithmetic and logic units, a further four logic units are also available.
Unlike the AMD equivalent chips, which only support dual-channel DDR2/1066 memory, the Core i7 processors, officially available from 17 November, offer three DDR3/1066 channels. Thus the chips have a theoretical memory bandwidth of 25.5GB/s, compared with the AMD chips' maximum of 16GB/s. Individual Nehalem processors are differentiated by the speed of the QPI interface. On the top model — the Core i7 Extreme 965 — QPI runs at 3.2GHz, but only reaches 2.4GHz on the smaller models.
Memory
According to Intel, the new Nehalem processors are specified up to a memory speed of DDR3/1066, while the current Core 2 architecture can be operated with DDR3/1600 memory. But according to the benchmark tool Everest 4.60, the internal memory controller supports up to 1333MHz. It could be that the system would not work stably in all situations at that frequency, so Intel opted for the more conservative specification. For optimal performance no more than three memory modules should be used. If four DIMMs are used, memory performance falls because the important memory parameter Command Rate can only handle two wait states.
Nehalem processors offer a built-in overclocking feature called Turbo Mode. If a piece of software fails to make full demands on all the cores, the chip's internal logic ensures that calculations in the cores that are in use operate at a higher clock speed. Last but not least, the Nehalem processors come equipped with SSE4.2, a command set extension that might be particularly useful for accelerating processing of string variables in search engines. Programs such as browsers, email clients and text processing programs could also benefit from the faster processing offered by SSE4.2.
Power consumption
In terms of power consumption, the system with the Nehalem Core i7 965 Extreme processor core ranks about the same as Intel's previous best-performing chip, the Core 2 Extreme QX9775, although the Nehalem processor, with 731 million transistors, clearly has fewer electronic circuits than the QX9775 with 820 million. Because hyperthreading technology makes more intensive use of the arithmetic units than with the single threading cores, they take the same power overall as the more complex earlier designs despite having fewer transistors.
Power consumption (Watts): shorter bars are better.
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