7-7-7-20 DDR3 Compatibility

[troutmonkey]

Hello,
I currently have Patriot Viper DDR3 memory running with 7-7-7-20 timings at 1.9v.
If I were to purchace more memory (These ones) with 7-7-7-21 timings at 1.5v would I have an issue running the two together?
I currently have 4GB, and plan to buy another 8GB. Would I be better off mixing the two and having 12GB or having just one set with 8GB?

EDIT: more info
CPU: AMD Phenom II 550 BE
MOBO: ASUS M4A89TD
GFX: Nvidia 250 GTS

This is my first post here, hopefully all is in order. I read through the FAQ but it is horribly outdated.

Thanks for you help in advance.
~Troutmonkey

 

[o1die]

Yes. The 1.9 volt may run at 1.5-1.6 volts, but the timings will be higher. I did the same with 1.8 volt corsair and ended up with 11-11-11-30 for my timings at the lower voltage. It still ran, just less efficient. At slower speeds, the timing numbers are always lower, which makes the ram feel just as fast for normal applications. I recommend you get all the same ram sticks for two or four slots, and be happy with just 8 gb. Unless you do constant video work, you won't notice the difference with more ram.

 

[troutmonkey]

Thanks for the fast reply.
I will probably just stick with 8GB than, unless you know of any good 1.9v RAM (Hopefully enough for BF3 when it comes out)
Though just out of curiousity would the mobo automatically change the voltages, or is that something that would have to be done manually? Not really confident playing with voltage settings to much

 

[troutmonkey]

Best answer selected by troutmonkey.

 

[o1die]

voltage settings may or may not change automatically. I just requested a bios update from the manufacturer for an older chipset motherboard to lower the voltage. It jumps up with faster ram, but is too high.