Welcome to the community, mastram!
I'd second @Nuckles_56's suggestion.
However, I have to warn you that WD Green drives are slow and not suitable for gaming.
if you want a gaming HDD, I'd suggest to check out WD Black drives:
http://www.wdc.com/en/products/products.aspx?id=760
If you are going to use this drive for storage ONLY or backup, I'd keep the DVD drive and go with an external HDD since you've already had all your SATA ports used up.
mastram :
thanks for the reply ...........if i install games ,and other stuff like videos,music and make always attached to my desktop and saves dvd drive .will it work ????? or i may face a problem ......and i also want to know which has better performance wd my book 3tb or wd green 3tb
It's hard to benchmark the performance between an internal and external drive. We are talking about different things here.
WD Green is a reliable internal drive, it's designed for secondary storage with Intellipower that saves power and it also runs quieter and cooler:
http://www.wdc.com/en/products/products.aspx?id=780
My Book is an external desktop storage solution with a lot of features that come with it, like Acronis True Image for system backup and SmartWare Pro for local and cloud backup. It has USB 3.0 connectivity which gives a much better transfer speed than USB 2.0.
http://www.wdc.com/en/products/products.aspx?id=870
Even though WD Green is not one of the fastest internal drives, speaking in connectivity: SATA ports (internal HDDs) are fairly faster than USB ports (external HDDs).
Hope this helped.
SuperSoph_WD