How fast is each core in a dual-core processor?
I am debating between two systems (for simplicity):
(1) 2.9 GHz dual core processor
(2) 2.3 GHz quad core processor
Now, when I am considering this, I have a few specific questions I would like to answer.
First, how are the 'numbers' (the frequencies) really calculated and what do they mean? For the 2.9 GHz dual core, does that mean that each core is clocked at around 2.9 GHz or does that mean that each core is clocked at 2.9/2 = 1.45 Ghz? In the same way, does the quad core give a 'net' 2.3 GHz speed or is each core literally going at 2.3 GHz?
My hunch from things I have read online is that each core is actually going at the specified speed (I know that you cannot get 12 GHz from a quad core 3 GHz system unless your code is perfectly linear in parallelization).
My other question is, suppose that you have code running purely in parallel. At what point does an extra core enable that code to go faster simply because there is less OS (and other background task) interference?
For example, if I had the choice of 2.6 GHz dual core or 2.5 GHz quad core, even for single threaded programs, I would assume that the 2.5 quad core would go faster because the single thread will be interrupted less by other programs (including the OS).