Hey there, Hamim!
The WD Black 6 TB is one of the two models that has an increased cache size of 128 MB for faster read/write performance and transfer speed. Basically, the WD's Dynamic Cache technology improves performance in real time to allocate and optimize cache between reads and writes. The peak data transfer rate with its 7,200 RPM and 128 MB cache could reach 218 MB/s when connected to a SATA III (6 Gb/s) port.
You should check the drive specification sheet here:
http://products.wdc.com/support/kb.ashx?id=Ze4o9M
The WD Black HDDs are our performance drives, meaning they are specifically designed to deliver on it. They are perfect for gaming and demanding applications like video/photo editing programs and multimedia. The drive also has a dual-core processor that offers twice the processing capability as a standard single-core processor in most traditional desktop HDDs. This further maximizes the drive performance, especially when loading games or large multimedia files.
Another advantage of the WD Black drives is the fact that they come with 5-year limited warranty.
Here you can check more details and features about it:
http://products.wdc.com/support/kb.ashx?id=NVBSF1
Hope I was able to answer your questions!
Good luck & Happy Holidays!
SuperSoph_WD