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Page 1 of 5  With design of new K10 microarchitecture, by majority of critics, AMD bit off more than they can chew. In beginning K10 wasn’t designed for two or single core CPUs. For less cores it was necessary to take “rejected” CPUs and disable faulty cores, and that isn’t a cheap process. CPU with disabled core still has same surface area as quad core, and disabled part is totally useless. This can be profitable if yield is relatively low which will result in large quantities of “defected” CPUs. One of the reasons why we waited so long for KUMA core is low yield of Phenom CPUs which resulted in low amount of rejected CPUs that can be converted to Phenom X2.
Be that as it may be, for manufacturing process of dual core Phenom (K10 Athlon) redesign of existing core was needed, manufacturing of new lithography masks and few more months of research and development (R&D). CEOs from AMD made a decision that it would be better and cheaper (and faster) to offer CPU with older K8 core at lower price. As result of that decision AMD with X2 CPUs couldn’t ward off Intel’s blows in price range below 100$ in form of Core 2 Duo CPU when it comes to overcloking. With Brisbane core at slightly higher frequency, AMD had good alternative compared to Intel Pentium E2XXX and Celeron 1XXX CPUs.
All this was price that to be paid for design of native quad Phenom (Barcelona core). On the other hand, Intel had dual core CPUs made in 65nm and 45nm manufacturing process that were, thanks to multi chip module, made into “quad core” CPUs. Although in some situations scalability of performances of those CPUs was not best, in practice, especially in desktop segment, this concept was proving itself as very good solution. So we can conclude that AMD rushed with promotion of monolithic quad core in 65nm, and was late with promotion of more efficient dual core CPU.
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Performances and Overclocking
New Athlon, based on Kuma core is real refreshment on AMD scene. New K10 core is, on average, 15-20% faster than older K8 core. In some situations this difference can be even 50%. We have already reviewed K10 microarchitecture and its advantages over K8 core. New Athlon X2 (Kuma core) compared to original K10 architecture has L3 cache (Level3 cache), support for 128-bit SSE instructions in one pass, faster and more efficient cache architecture and more. Kuma core is at 2.7GHz (slowest one) efficient as old Athlon 64 X2 6000+ at 3.0GHz with 2x1MB L2 cache, while in processing demanding operations like video compression, rendering and games is even more efficient. In the same time we must point out that those 2.7GHz is highest default frequency for any CPU based on K10 architecture.
Clock-per-clock performances of Kuma core are equal to Conroe 2m/4m cores. In some situations Conroe is maybe slightly efficient but in operations that demand massive memory bandwidth and lot of multitasking K10 X2 (Kuma) is good rival for Intel Core 2 Duo CPUs. Overclocking possibilities are surprisingly good and we could say that AMD with Kuma core is dangerously close to overclocking possibilities of Intel Core 2 Duo CPUs made in 65nm manufacturing process.
We tested Athlon X2 7750 on DFI LanParty DK 790FXB M2RS motherboard and with better air cooled solution we managed to extract respectable and stable 3.4GHz for cores and 2.4GHz for northbridge. In most of benchmark applications X2 7750 was stable even on 3.5GHz. Unfortunately frequencies of 3.6GHz and higher can be achieved but not with conventional cooling solutions. As reference in results we used pricier Phenom X4 9950 Black Edition.
When Athlon X2 is overcloked, increase of performance levels are great thanks to L3 cache and massive memory bandwidth.
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Processors 
