I heard that a CPU can bottleneck the GPU but what is bottleneck and what does it happen?

Just need some clear explanations on that.

The CPU feeds data to the video card. If the CPU cannot supply the video card with data as fast as it can process it, the CPU becomes a bottleneck.

http://en.wikipedia.org/wiki/Bottleneck_(engineering)

you should've googled!

bottleneck is the part of the bottle that the sweet sweet brew must pass through before it gets to your mouth (if drunk from the bottle)

A bottleneck is a limiting factor.
A CPU can be a bottleneck when it is not fast enough to keep a fast GPU supplied with frames to be displayed.
A GPU can be a bottleneck when it can not display those frames at an acceptable rate.

SO a fast GPU will cause the CPU to bottleneck as it can't cope with the power of the GPU!!!

SO faster the CPU lesser will be the bottleneck effect.

Not exactly.
There is always some limiting factor.
In the same PC, the factor might change from moment to moment.

What you are looking for is some semblance of balance among all of the parts.

Foe example:

Would you put 13" wheels on a 1000hp dragster?
Would it be effective to put a lawnmower engine in a dragster with 40" wheels?

That anolgy with the dragster is exactly it - If you had something like an Intel Extreme Edition Quad core overclocked to some insane Clock speed and 8 GB of 1333 MHz DDR3 paired with say, an ATI Radeon 9800, the GPU would be a bottleneck, and vice versa, if you had a GTX 280 with a Pentium 4, the CPU would be a bottleneck.

well yes i would put 13" wheels on a dragster! so wat if they're on the front

the bottleneck in a system is ALWAYS the HDD.thats the slowest thing in a computer system. of course nowadays SSD solve that problem.

^yeah except tell me the cost per gig of a SSD compared to a 640gig HDD

yeah i know.thats why i dont reccomend anyone to those 10K raptor and hugely expensive SSD!lol

pffffffff the original raptors are now owned by the WD AAKS model drives. 320gig version has a single platter two of them in RAID 0 = ownage

for less than a third of the price of a velociraptor too

they are currently developing a 20k raptor as well!sigh... when do they give up???lol

If your workload is hard drive intensive, then it pays to get a fast hard drive, as that will be the limiting factor.
There is generally no real world(vs. synthetic transfer rate benchmarks) performance advantage to raid of any kind.
Go to www.storagereview.com at this link: http://faq.storagereview.com/tiki- [...] iveVsRaid0
There are some specific applications that will benefit, but
gaming is not one of them. Even if you have an application which reads one input file sequentially, and writes
it out, you will perform about as well by putting the input on one drive, and the output on the other.
If you need capacity, then large drives are better because they are cheaper per gigabyte.
If your needs are for limited storage capacity, and high HDD performance, then a v/raptor or SSD is the correct choice.

Needs are different, so one size recommendation does not fit all.