Best memory for MSI 790FX-GD70

Get DDR3 1333 RAM with low voltage (1.5V-1.65V) and low latency (CL=7)

See this thread for reasons
http://www.tomshardware.com/forum/264089-30-choosing-me...

Even though you have an AMD rather than i7 and CAN use higher voltage, I would stick to lower because they tend to be newer design and higher quality. Don't worry if modules say i5/i7 compatible, there's nothing to this. You don't need XMP for your system.

http://www.newegg.com/Product/Product.aspx?Item=N82E168...
This is a good choice

thanks for the fast reply

and do you think 4GB is enough? how about 6GB or 8GB?

You want either 4GB or 8GB because the cost of 2 - 1GB modules makes buying 2 - 2GBs a better deal. And you need matched pairs of RAM to use dual-channel - that's highly desirable.

How much you need depends upon your usage. Less than 5% of computers today have even 4GBs of RAM.

Thank you very much I think 4GB is enough