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http://www.apple.com/imac/specs.html


Processor and memory
21.5-inch and 27-inch models, one of the following:
3.06GHz Intel Core 2 Duo processor with 3MB shared L2 cache
3.33GHz Intel Core 2 Duo processor with 6MB shared L2 cache
27-inch models only, one of the following:
2.66GHz quad-core Intel Core i5 processor with 8MB shared L3 cache; Turbo Boost dynamic performance up to 3.2GHz
2.8GHz quad-core Intel Core i7 processor with 8MB shared L3 cache; Turbo Boost dynamic performance up to 3.46GHz; Hyper-Threading for up to eight virtual cores
4GB (two 2GB SO-DIMMs) of 1066MHz DDR3 SDRAM; four SO-DIMM slots support up to 16GB

EDIT: Sorry if that didn't answer your question fully.
 
Do note the gpu is mobility 4850, and not desktop 4850. A lot of benchmark programs can't tell the difference, because the mobility 4850 has the exact same numbers and features as desktop 4850, except it's clocked lower. The performance loss is negligible compared to other mobile cards because of this. Expect the performance to be in the realms of desktop 4830-- with a memory bandwidth of 54gb/s compared to 64.
 
CPU is an i7 860 (the i5 is a i5 750), and the GPU is a "mobile" HD4850 which is really just a downclocked desktop HD4850
 
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