Mixing RAM when adding it to a desktop

Factual Questions
1

I’ve always been under the impression that it’s generally not a good idea to mix types of RAM in a system. This notion has probably been with me since building 386 machines, so I don’t know how relevant it is to today’s architecture; it’s just something I’ve always stuck to.

Does it still hold true?

[backstory]
I just ordered 12 GB of RAM. My intent is to replace the 6 GB currently in my machine. But do I need to? Can I just add it and end up with 18 GB of RAM?

Here’s the basic hardware (it’s a couple years old):[ul][li]Asus P6T motherboard[/li][li]i7-920 (Bloomfield)[/li][li]Crucial 128GB SSD[/li][li]2x HD 5770 (crossfire)[/li][li]Win 7 64-bit[/li][li]Nothing is overclocked[/li][/ul]
The RAM that’s in there now is 6GB of G.Skill memory (3 x 2GB). The RAM I ordered is G.Skill Ripjaw (3 x 4GB). The speed (PC3 1600/12800), timings (9-9-9-24) and Cas Latency (9) are all the same. The only differences I can see are the two-year manufacturing span and the Ripjaw’s cool-looking cooling fins (not that I’ll ever see them once the case is closed up again).

The motherboard has 6 DIMM sockets, so all six sticks will fit. The board also takes a maximum of 24GB, so unless there’s an issue with 18GB, that shouldn’t be a problem.

So, am I asking for trouble if I try and use everything? Should I leave well enough alone and stick with “just” the 12GB? Since this is my primary work machine, I’d rather not experiment to just see what happens (would hate to BSOD in the middle of a project).

Or given that the manufacturer and basic stats are the same, are problems unlikely?

Lastly, if I do add them, any advice as to how to fill up the slots?

No, really lastly this time. Now I’m confused. Checking the motherboard’s manual, it says under 2.4.2 Memory configurations: “you may install 1GB and 2GB unbuffered and non-ECC DDR3 DIMMs into the DIMM sockets.” That seems to say that the 4x3GB sticks won’t work. But I got to those sticks through two or three different memory configurators, including Crucial’s “scan my system” application. They all returned hits for the 3x4 configuration. What gives?

Thanks,

Rhythm

2

I’ve seen computers mix 2G and 4G sticks without trouble, even when they were from different manufacturers and had different latency. Using identical RAM is a good policy, but modern computers are usually pretty flexible about it. (I think I’ve even seen a computer mix different speed RAM, automatically underclock the faster stick, and proceed without a hiccup. I’m not certain, though.) I’d make sure your computer works with the new RAM and then at least give it a try with all six pieces. It looks like that’s a triple channel motherboard (two channels with three slots per channel), I’d split the RAM accordingly. The manual should be able to identify which slots are which channels, Asus usually color codes them as well. If the computer really doesn’t like it, it will probably refuse to boot or bluescreen in short order. A couple hours of a standard stress test will tell you if it’s going to be reliable or not. Asus and G.Skill both make good products, I’d actually be kind of surprised if it doesn’t work.

The line of the manual that you quote seems to be saying that the motherboard can take (or will only take) 1GB or 2GB DIMMs. That makes very little sense, I can’t imagine that it would be unable to handle 4GB sticks. It’d have to, in order to reach the 24GB maximum. I’d ignore it as a typo or possibly a bad translation, especially since you have several sources that contradict it. Asus has mistakes in their printed material like that every once in a while.

Let us know how it works out!