Upgrading PC. Ram Questions

[nfuzer]

Ok, I don't know much about RAM. When i built my computer, the RAM that I got came with the bundle so I did not research it nearly as much as my other parts.

So this is my system specs:

GPU: XFX HD- Radeon HD 4890 1GB
MOBO: ASUS M4A78T-E AM3 AMD 790GX HDMI ATX AMD Motherboard
RAM: CORSAIR XMS3 DHX 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800)
CPU: AMD Phenom II X4 945
PSU: Antec TruePower e 750W
OS: Windows 7 Ultimate x64

So the question is, what RAM should I add to my computer? I want to have 8GB of RAM. I am unsure of a few things:

Does the RAM I add need to be the exact same?
Does the RAM I add need to be the same brand?
What do i need to know when upgrading my RAM?
And Lastly, what the hell does timing mean? (8-8-8-24; 9-9-9-24...ect)

My plan was to purchase: http://www.newegg.com/Product/Product.aspx?Item=N82E16820145249

Or

http://www.newegg.com/Product/Product.aspx?Item=N82E16820145263


Sorry for asking questions that probably seem so simple.

Thank you for taking the time to answer.

 

[Maziar]

Brands doesn't matter but its recommended to use a RAM with same voltage,speed and timings of your current one, because if they don't have same specs,then you have to change the settings of one to reach the other model's specs and it "may" cause instability.
As for timings,well they don't affect the performance much,they are mostly important for OC'ng.(lower timings are better for OC'ng)

 

[nfuzer]

So arises the question,what ram should i buy?

 

[1haplo]

What are your current timings? The XMS3 DHX has 2 timings the C7 is 8-8-8-24 and the D9 is 9-9-9-24.

If you do not know download CPU-z and it will tell you what the timings are. If the timings are 9-9-9-24 get the Dominator (Because of the MIR) if your timings are 8-8-8-24 get the XMS3.

IF your current timings are 9-9-9-24 and you get the 8-8-8-24 both sets will run at 9-9-9-24
or your current timings are 8-8-8-24 and you get the 9-9-9-24 both sets will run at 9-9-9-24

The XMS3 is better RAM because it has lower timings and lower voltage.

 

[nfuzer]

Best answer selected by nfuzer.