Intel CPUs: Core i7-870, Core i7-975 Extreme, Core i7-980X Extreme, And Core i7-2600K
The Core i7 brand is used to label multiple different processor line-ups. Although there are dual-core mobile Core i7s available, on the desktop, a Core i7 is going to be a four- or six-core chip.
The Core i7-870 processor is based on the 45 nm Lynnfield architecture and has four cores, but can execute eight threads in parallel thanks to Hyper-Threading support. The architecture is similar to the Core i5-750, but the base clock is higher, there's more Turbo Boost headroom, and the Core i5s don't come with Hyper-Threading. Also, Lynnfield never got AES-NI functionality. You can find details about this CPU in the article Intel Core i5 And Core i7: Intel’s Mainstream Magnum Opus.
The Core i7-975 Extreme Edition centers on the 45 nm Bloomfield design (the very first Nehalem-based chip to emerge back in 2008). This particular model was launched in 2009, features four cores, 8 MB of shared L3 cache, and a clock rate that scales up to 3.6 GHz in single-threaded apps (and a base 3.3 GHz frequency).
Due to its age, this CPU lacks features like Trusted Execution, VT-d, and AES-NI, however. More details can be found in Intel Core i7-975 Extreme And i7-950 Reviewed
The Core i7-980X Extreme Edition, code-named Gulftown, is the second-fastest processor in Intel's line-up, behind the Core i7-990X. It is manufactured using a 32 nm process, and sports six cores with a total of 12 MB shared L3 cache. Very shortly, the entire Gulftown family will be displaced by the hexa-core Sandy Bridge-E design, sporting an integrated quad-channel DDR3 memory controller and 15 MB of shared L3 cache.
The article Intel Core i7-980X Extreme: Hello, Six-Core Computing presents details of the Gulftown CPU.
Last but not least is Intel's Core i7-2600K. This is another modern processor, based on the Sandy Bridge design. In contrast to Core i5-2500K, its four cores support Hyper-Threading. A base clock of 3.4 GHz accelerates up to 3.8 GHz In single-threaded applications. Our article Intel’s Second-Gen Core CPUs: The Sandy Bridge Review breaks down the details of this CPU's architecture.