Usually we heard about core i5, core i7 etc. but in the recent years we hear about dual core i7 and quad core i7 etc. This confuses me. Does it generally mean that they have double and quadruple performance respectively as compared to core i7 computer?
One core meant:
One core meant it could follow one set of instructions at a time.
These could follow two instruction sets simultaneously.
Triple core and Quad-core followed suit, with three or four threads respectively.
Then Intel introduced Hyper-Threading ---> The ability for a single core to follow two threads. All Core i3's, i5's, and i7's are hyper threading.
This means that a Dual-core i7 can follow up to Four threads simultaneously, while a Quad-core can follow up to Eight.
For a power user, from which it sounds like you are, a Quad-core is the way to go.
First off, I'll limit my answer to current generation (6th gen desktop) Core-i5 and Core-i7 models, this makes it very easy since there's not a whole lot of variation core-wise.
All 6th generation Core-i5 processors have 4 cores, this means they can execute 4 concurrent operations.
All 6th generation Core-i7 processors have 4 cores with hyperthreading, this means they can (theoretically) execute 8 concurrent operations. I believe there are some technicalities regarding how well hyperthreading works for certain tasks though.
Dual or quad Core-i7 might also mean that a system has multiple processors. This interpretation depends very much on how it's actually written.
If someone writes "I have a quad Core-i7 system", I assume they mean that their system contains four separate Core-i7 processors - each of which has 4 cores.
However, if someone were to say "I have a Quad-core Core-i7 system", I assume their system contains a single Core-i7 processor - which has 4 cores.
this second interpretation is a little far fetched, since I don't think people really say that, but it might be possible.