need help about dual cores & quad cores

ok so im looking to buy a computer but i dont understand how these cores are running in the computer

eg

eg http://www.pcworld.co.uk/martprd/st...u=056078&page=Product&fm=null&sm=null&tm=null

it says 2.1 ghz dual core, now what i want to know is that

is each core running at 2.1 ghz? or the overall 2 cores is at 2.1 ghz?

also when it says 2.4ghz quad core how many ghz is each core?

 

It means 2 cores, each running at 2.1. This does not mean you get a 4.2, but 2x 2.1 . For multi tasking its great, and more and more apps are supporting it.
For a quad, irs 4 cores each at 2.4 , same as above

 

thank you for your help

do u recommend me getting a quad core or dual core?

i do use mostly photoshop, word programs, internet surfing etc

no hardcore stuff