Technically it has got 8 cores, so they have every right to call it octa-cores. Because really, there is 8 cores to it regardless of how many are being used at a time. If you have a castle, but you choose to live in the garage of the castle, you would still tell people you live in a castle, right? and you wont be wrong at that, because the garage is inside the castle.

But I also believe they do it for marketing purposes, and in that, some might be fooled to think that 8 cores is being used. Isn't that what marketing is all about?

S2. 

Design is in one of  my bottom list of priorities in buying any phone. Some treat this as most important criteria. I still cannot understand such mentality. Some users said I have no taste !. Guess I am too old to appreciate designs.
I find completely nothing wrong with the plastic quality used in all recent Samsung Galaxy phones. It is only some users like to bash about it over use of metallic, aluminium or glass. Some of them talk as if the Samsung designers are stupid and has no taste and only they themselves possess such finesse.
Seriously the Xperia Z , some users including many web reviewers praised its classy look. I don't find it classy at all - to me it is just a piece of rectangular glass slab. Anytime I'd prefer say S3 or Note2 design over it. I bought it mainly to have a try again at Xperia range after my last disappointment with the Arc.
All those who always talk about classy designs, get a Vertu phone - than you can talk about class. Is only a phone, why the need to have class in its design ?? I find practically and features is more important
And worse of all, 9/10 of such users will buy a casing and protect /hide these "classy" designs !!!

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How great plastic build, plastic never can be category under elegance or premium.

S 4 is not ugly, it still look nice the front, nothing wrong with plastic, but whatever Samsung put at back cover look kind of not high quality build, that was design and surface pick issue.

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oh here we go again... plastic and the defender of non plastic + design 
why everytime come here also same topic   

Now a few words about the screen. As you remember, the main complaint about the team superhumans endowed supernormal (X-ray vision, a hundred-fold increase in the image on the retina of the eye) was the presence of PenTile (pixel formation of a smaller number of sub-pixels). We, the ordinary people doing reviews of devices, even got special microscopes and lenses to show horrific PenTile and superheroes to make a fatal mistake when choosing a phone. In Galaxy S4 is even worse - mean engineers changed the structure of sub-pixels (they are now equal in size), and created a density image at 441 dots per inch. I think that even superhumans to see the individual pixel will need to use sverhuvelicheniem - see the structure of the screen if you are not from the planet Krypton, is impossible. But I am sure that many will blame for PenTile and the machine - for good old habit. Stupidity, as a rule, long-lived phenomenon.