RAM upgrade with mix of DIMM sticks on ASUS B85M-G

[pjun]

I have 2 DIMMs installed, 4GB each in first and 3rd slot. So total is 8GB.

Can I add an 8GB DIMM on one of the empty slots to get a total of 16GB and later add another one to make it 24 GB?

The mobo has 4 slots and can take max of 32GB support.

 

[pjun]

Currently it is Kingston HyperX 1600 and plan to buy the same for 8GB DIMMs.

Using Windows 8.1

 

[norsestar]

It will probably work, but may or may not work dual-channel or may require a drop to 1333 or may just refuse to work at all. The safest answer would be to run one matched pair.

What OS are you running? Windows 7 Home Premium 64-bit has a 16GB RAM limit that would prevent you from utilizing 24GB...

 

[pjun]

Thanks norsestar. I am running Win 8.1.

I am ready to live with single-channel.

How should I insert the DIMMs? A0 = 8GB, A1, A2 = 4GB each and leave A3 empty for now?

Also, is it more likely to work if I use two 4GB and two 8GB. i.e. 2 matched pairs?

 

[norsestar]

The manual I'm looking at lists the DIMM socket labeling as DIMM_A1 (black, closest to CPU), DIMM_A2 (gold), DIMM_B1 (black), DIMM_B2 (gold, farthest from the CPU). Assuming this, I'd try the 2 4GB DIMMs in A1 and A2 and the 8GB in B2. This puts 8GB on each channel and the single DIMM on the farthest slot from the CPU. This sounds like it should give you the full 16GB in dual-channel.

Yes, it's more likely to work in matched pairs but if you've got the parts already you may as well try it and it will probably work.

 

[pjun]

Thanks nosetar.

What I have heard and read is that the largest DIMM should be closest to CPU ie in A1 and the others in same colored pair ie A2 and B2.

That is

A1 (black) = 8 GB
A2 (gold) = 4 GB
B1 (black) = Empty
B2 (gold) = 4 GB

What you are suggesting is:

A1 (black) = 4 GB
A2 (gold) = 4 GB
B1 (black) = Empty
B2 (gold) = 8 GB

So this is totally different. Are you sure about your suggestion?

BTW, How do I verify that I am getting Dual-channel 16GB or not?

 

[pjun]

I am seeing 16GB in system properties (using 8-4-Empty-4 setup) but real question now is how do I check if I am getting dual channel performance?

 

[norsestar]

You will want 8GB on Channel A and 8GB on Channel B to get full dual-channel performance. With 12GB on Channel A and 4 GB on Channel B, I would expect you've got the 4 GB on Channel B in dual-channel mode with the first 4GB on Channel A and the other 8 GB on Channel A in single-channel mode. I know my machine is in dual-channel mode because it prints something like "8 GB in Dual-Channel" during POST. If your BIOS doesn't say, you could benchmark the memory to measure the speed. I haven't tried that, so I'll leave it to someone else to recommend a good tool for that.

I suggested the 4-4-Empty-8 setup to try to give you best electrical environment (which should let you run as fast as possible). A single DIMM should be in the channel's farthest slot from the CPU to minimize electrical noise, hence the 8GB in B2 and B1 empty. Two DIMMs on a channel is electrically more challenging than a single DIMM so I put the two 4GBs in Channel A, closest to the CPU. (Actually, I'd expect that if you peeled the board apart you'd find the trace lengths have been matched for both channels, but Channel A *looks* closer...)