a quad core processor is just one processor, even a hex core or a octa core processor is still one single processor.
In plain English:
Think of a single core processor as like a motorbike
A dual core processor like a sports car
A quad core like a stock car
A hex core more like a minivan
and a octa core more like a small bus.
All of these things have their advantages and dis advantages
Now granted there are processors with way more then 8 cores, last time I checked the top processor record so far is 72 cores.
But does this mean that processor is the best?
No as it has drawbacks such as being quite large.
Also such processors are better for servers rather than desktops.
The most common type of processor right now is either quad core due to it being right in the middle and offering great performance per dollar or dual core.
Dual cores are slowly phasing out though, technology has made them slowly become less appealing.
But core count isnt the only factor.
Sometimes having more cores does have its disadvantages as most applications are not optimized for more than dual core.
Quad core is adopting quite quickly though.
Look at it this way, this whole time the industry has been making SUV's but now smaller more gas efficient cars are becoming more popular.
Its like how in the 70's the muscle car faded out due to high gas prices, you still see them in modern times but they have faded out of popularity for a reason.
Single core processors are kind of like The Model T, not even found anymore except for collectors.
Dual cores are like the Muscle cars, you dont see too many of them anymore