The Core i5 661 CPU, Core i3/i5 Series
The Core i5 661 will cost about the same as the existing Core i5 750, but as you know the new processor carries an on-die GPU. The i5 661 will also hum along to the tune of 3.33GHz, while the i5 750 operates at a more modest 2.66GHz. Despite the clock speed advantage, the 661 only feature two physical cores, whereas the Core i5 750 features four.
This applies to all four processors in the Core i5 600 series, which also feature half as much L3 cache as the Core i5 750. That said, it is certainly worth noting that while the Core i5 750 does not support Hyper-Threading, all Core i5 600 series processors do, allowing them to handle up to 4 threads simultaneously.
Another feature present in all Core i5 600 CPUs is Turbo Boost, which was a very beneficial feature of the Core i5 750 processor. The way Turbo Mode worked with the Core i5 750 was that when three or four cores were active the default clock multiplier, being 20x, was increased by a single step to 21x, boosting the core frequency by exactly 133MHz.
However, if only two cores were active the multiplier was boosted to 24x, resulting in a 533MHz clock speed increase. Finally, if just a single core was in use the multiplier was boosted to 25x, resulting in a huge 667MHz frequency boost, taking the Core i5 750 from 2.66GHz to 3.32GHz.
Turbo Boost is configured a little differently on the Core i5 600 series because these processors tend to operate at higher frequencies and only have two cores. When both cores are active the multiplier can be boosted by 1x, so for the Core i5 661 that would take the multiplier to 26x, resulting in a frequency of 3.45GHz. If just a single core is active then multiplier is boosted by 2x, taking the Core i5 661 to an impressive 3.60GHz frequency.
The Core i5 600 series feature a 4MB L3 cache with each core receiving its own 256KB L2 cache. The Integrated Memory Controller (IMC) supports dual-channel DDR3 memory at officially supported speeds of up to 1333MHz. Like the Core i5 750 the new 600 series drops the Front Side Bus in favor of the DMI (Direct Media Interface).
As a side note, the Core i3 5xx processors that are also debuting this week will basically feature the same specs as the Core i5 Clarkdale CPUs. Similar L2 and L3 cache configurations, same built-in GPU, slightly lower clock frequencies, with the key difference being the removal of Turbo Boost mode. The Core i3 530 (2.93GHz) will cost $113, and the 540 (3.06GHz) will be a bit more expensive at $133.
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