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AMD usually builds server processors with the cores similar to desktop ones that differing a little by external interfaces support: they have more HyperTransport busses and the memory controller is designed to support Registered memory DIMMs. Istanbul core stands out of this rule: so far it has no desktop analogue. Although we can’t deny that Istanbul, just like Shanghai, is close to Deneb in microarchitecture. However, in this case the differences go beyond the memory controller and the number of HyperTransport busses. Istanbul has six computational cores on a single processor die, which makes these processors the most expensive solutions in the Opteron lineup: they are priced starting at $450. There is nothing surprising about it: Istanbul die size is 346 mm2, which is about 1/3 larger than Shanghai die. The six-core processor has 904 million transistors. All this fits onto a monolithic semiconductor die, which holds not only six computational cores each with 512 KB L2 cache, but also a shared 6 MB L3 cache.

Istanbul processors have three HyperTransport busses, which allow using them in dual-, quad- and eight-processor systems. As for the memory controller, Istanbul works with Registered dual-channel DDR2-800/667/533 SDRAM with or without ECC support in order to maintain compatibility with existing Socket F platforms. By the way, compatibility is another specifically stressed advantage of AMD server processors: Socket F platform was first introduced three years ago, but even the latest Istanbul CPUs work perfectly fine with any Socket F mainboards after reflashing the BIOS. However, if we regard Istanbul as a possible solution for a single-CPU platform, then there is no need for HT Assist and three HyperTransport busses. However, even in this case Istanbul may offer special advantages over Deneb and Shanghai, even if we do not take into account more computational cores. First, Istanbul supports higher HyperTransport bus frequency that has been increased to 2.4 GHz (in contemporary desktop AMD processors this frequency doesn’t exceed 2.0 GHz). Second, the built-in L3 cache inside Istanbul processor is overclocked to 2.2 GHz instead of 2.0 GHz.

As for the six-core processor clock frequencies, they are obviously lower than the frequencies of quad-core CPUs. The top AMD Opteron processor models with six cores work at 2.8 GHz. Moreover, these solutions belong to HE class that includes CPUs with higher power consumption and heat dissipation. The general-purpose six-core Opteron processors with average CPU power of 75 W work at 2.6 GHz maximum frequency, which is 30% less than the frequency of top quad-core Phenom II X4 CPUs. This must be another reason why AMD is not in a hurry to move their six-core processors into the desktop segment: at this point their clock frequencies won’t let them outperform the top quad-core CPUs even in well-paralleled tasks. For our today’s test session we picked a six-core Opteron 2435 processor working at 2.6 GHz clock frequency. Opteron 2435 is the top Istanbul model of those widely available in retail these days. It costs around $1000, but when these CPUs will be available in the desktop segment, they will most likely be considerably cheaper. Opteron 2435 processor is a server solution that is why it has a 1207-pin LGA packaging and differs substantially from the usual Socket AM2/AM3 CPUs even in its exterior looks.

Overall, the CPU with six computational cores can really raise the performance bar. Two additional cores provide a pretty significant advantage during video processing and transcoding as well as during final rendering. In other words, adding additional cores to desktop processors indeed makes a lot of sense. But unfortunately, gamers will hardly be excited about the six-core desktop processors. Most games at this point can’t respond to the increase in the number of computational cores with an appropriate fps rate growth. But we can certainly find a few examples of just the opposite.

Izvor: X-Bit Labs