Machine runs fast with 16GB but dreadfully with 32GB

[tricky]

My colleague has a PC based around an i7 2700k CPU running Windows 7. The board is a Gigabyte GA-Z68XP-UD3-iSSD with the latest BIOS installed (which I did in attempt to solve the issues earlier today).

We are having various stability issues with it. In trying various things, we find that the machine runs fast and smooth with just 2 of the 8GB sticks installed (16GB total). When we install all 4 of the 8GB sticks (32GB total) the machine has started to behave incredibly sluggishly, taking several minutes to become responsive after starting up. Using just 2 of the sticks works fine. We have tried this several times, and the machine now refuses to work properly with all 4 sticks (32GB total) installed.

In desperation, we have even replaced the ram with the stuff from my machine! Same problem!

What could cause a machine to run normally with 16GB but slow as hell with 32GB?

[Morbid Angel]

This is a guess, but could it be that the ram has not enough voltage?

[Donald2B]

I'm not familiar with that motherboard, but here are a few of my thoughts on the many machines that I have built.

- did memory come as a 4 stick kit?
I've had two 16GB kits bought at different times with exactly the same specs, NOT work.

- make sure you are using the correct spec memory. 1.5 vs 1.6
- 1.6 will NOT work well in a 1.5v motherboard and vise versa

- some lower consumer grade motherboards don't like to have all memory slots filled with the top speed ram they are rated for. Might need to step down a speed setting.

That's mostly what I can remember from building the iCore7 machines.

[tricky]

This is a guess, but could it be that the ram has not enough voltage?

I'm very wary about messing with voltages. What would you suggest I increase it to (so that I don't fry the machine!)?

[tricky]

I'm not familiar with that motherboard, but here are a few of my thoughts on the many machines that I have built.

- did memory come as a 4 stick kit?
I've had two 16GB kits bought at different times with exactly the same specs, NOT work.

- make sure you are using the correct spec memory. 1.5 vs 1.6
- 1.6 will NOT work well in a 1.5v motherboard and vise versa

- some lower consumer grade motherboards don't like to have all memory slots filled with the top speed ram they are rated for. Might need to step down a speed setting.

That's mostly what I can remember from building the iCore7 machines.

Initially, they were bought as 2x16GB kits, but we have tried the ram from my machine which was a 32GB kit. Same problems.

We will check the ram voltages. The thing is, there is the XMP profile which should read all the correct settings for the ram, but enabling this doesn't help at all. In fact, it always seems to crash on boot up and restarts saying that the system overclocking is not stable. We haven't overclocked!

[alexyork]

Have a look at updating the BIOS, although be careful to backup your current one (note down all of the settings) and be aware that this could brick your machine. Might be best to talk with the mobo manufacturer and ask them about compatibility that specific amount of that specific ram.

Also check they're in the correct slots if running in dual, quad or triple channel.

You might just need to reset the CMOS (this resets BIOS settings) and Load Optimized Defaults (then re-do any custom settings you might need/want to).

And, as someone else said, check the voltages are correct for all the modules. It might be that the voltage/timings are wrong for the newly-installed modules. Compare against the original ones and see if any differences.

[tricky]

Have a look at updating the BIOS, although be careful to backup your current one (note down all of the settings) and be aware that this could brick your machine. Might be best to talk with the mobo manufacturer and ask them about compatibility that specific amount of that specific ram.

Also check they're in the correct slots if running in dual, quad or triple channel.

You might just need to reset the CMOS (this resets BIOS settings) and Load Optimized Defaults (then re-do any custom settings you might need/want to).

And, as someone else said, check the voltages are correct for all the modules. It might be that the voltage/timings are wrong for the newly-installed modules. Compare against the original ones and see if any differences.

I have installed the latest BIOS and our settings are always/have always been pretty much generic. We tried removing the CMOS battery for a few minutes, but that didn't even help. This is a reasonably good board (mid-range) with decent quality RAM. Very strange.

[alexyork]

I have installed the latest BIOS and our settings are always/have always been pretty much generic. We tried removing the CMOS battery for a few minutes, but that didn't even help. This is a reasonably good board (mid-range) with decent quality RAM. Very strange.

Think you're going to have to talk with the board manufacturer then. Does sound strange. Did you load the optimised defaults after resetting the CMOS though? Otherwise it'll all be running in a Fail Safe config.

[Donald2B]

I agree with Alex. Try resetting the BIOS, especially after a BIOS update.

I would verify the voltage of the memory you have purchase. 1.5v or 1.6v. This makes a HUGE difference. It almost explains why XMP is having issues because if you have 1.5v RAM in a 1.6v board, it is already running out of spec and will cause issues. I know I have to be VERY cautious when ordering memory to make sure I get the correct voltage for the motherboard.

The other thing I would try, is swapping RAM into your workstation. You mentioned that you used the memory from your machine in the problem one. Try the opposite, use the memory from the machine not working into yours to verify that the memory is in fact okay.

[tricky]

Think you're going to have to talk with the board manufacturer then. Does sound strange. Did you load the optimised defaults after resetting the CMOS though? Otherwise it'll all be running in a Fail Safe config.

I can't say that I did that specifically. Will give it a try.

[tricky]

Just looking on the Gigabyte website, the specs seem to suggest 1.5V RAM is fine:-

1. 4 x 1.5V DDR3 DIMM sockets supporting up to 32 GB of system memory
   * Due to Windows 32-bit operating system limitation, when more than 4 GB of physical memory is installed, the actual memory size displayed will be less than 4 GB.
2. Dual channel memory architecture
3. Support for DDR3 2133/1866/1600/1333/1066 MHz memory modules
4. Support for non-ECC memory modules
5. Support for Extreme Memory Profile (XMP) memory modules

The RAM we are using (this is now the stuff from my machine) is as follows:-
Corsair Vengeance
CMZ32GX3M4X1866C10
32GB (4x8GB) 1.50V ver 4.21

I actually have my colleagues RAM (from the bad machine) running in mine and it is absolutely fine.

[super gnu]

did you try running with 3 sticks in there? might be a duff memory slot. failing that a duff memory controller. one means replacing the mobo, the other means replacing the cpu..

edit: could also try swapping the 2 sticks you know are ok in that machine, into the other 2 slots.. same thing really.

[Donald2B]

Well that rules out mismatched RAM and it's good since it works well in your computer.

So everything is pointing to the motherboard. I would contact Gigabyte and see if they can help you walk through some troubleshooting tips.

It appears to me, the motherboard probably has a bad memory slot, preventing XMP from selecting the appropriate RAM settings in the BIOS. So windows is not running well due to the Memory issues, which you have already figured out.

If you need this machine up and running immediately, you will probably need to buy another motherboard while you work with Gigabyte to figure out what's wrong with the old one. It can take some time depending on how willing they are to help you. I have had mixed results with their support, so I no longer use/recommend their products.

[tricky]

This is a nightmare to troubleshoot!

It seems that we can get the system booting and running (apparently) normally with 3x8GB sticks inserted. It doesn't seem to matter which slots we fill. Having all four slots populated seems to bring Windows to a crawl. We have tried numerous BIOS defaults and other BIOS settings put cannot solve the problem.

All I can say is it doesn't seem to be a physical memory slot that gives the problem. Its just having 4 memory sticks installed. Does this suggest the CPU has developed a fault?

[super gnu]

in this case sounds like it could be the memory controller on the cpu.. youve maybe got some instability when its being stressed .. you could try manually upping the voltage to the ram, or the memory controller (not advisable) or to test, downclock the cpu/ram..