Mismatched memory on Haswell?

[NTMBK]

Hi all,

I currently have a Haswell HTPC with 6GB of memory in it, a 4GB DIMM and a 2GB DIMM. I'd like to upgrade the amount of RAM I have, but I would rather not have to pay for an entire 16GB set. My question is, how bad is the penalty these days for mismatched DIMMs? If I replaced by 2GB DIMM with an 8GB DIMM, for a total of 12GB, would things mostly work alright?

Thanks!

 

[UsandThem]

Ideally your system would simply run at the speed of the lowest module (speed, timings, etc). This is what happens the majority of time.

However, sometimes combining different modules will cause system instability or even a failure to post in some cases. Unfortunately the only way to discover this is to:

A. Try it yourself
B. Be lucky enough to find a post where someone combined two different modules, and reported it worked or didn't work.

Ideally it is always best to run matched RAM.

 

[NTMBK]

Ideally your system would simply run at the speed of the lowest module (speed, timings, etc). This is what happens the majority of time.

However, sometimes combining different modules will cause system instability or even a failure to post in some cases. Unfortunately the only way to discover this is to:

A. Try it yourself
B. Be lucky enough to find a post where someone combined two different modules, and reported it worked or didn't work.

Ideally it is always best to run matched RAM.

Hmm, okay, thanks. Would I run into these problems even if I found a module with different capacity, which otherwise matched frequencies and timings?

 

[UsandThem]

Hmm, okay, thanks. Would I run into these problems even if I found a module with different capacity, which otherwise matched frequencies and timings?

If it was same spped/timings, same type of memory modules, etc, it would help. Most of the time there aren't any issues, but if you get the new module and start experiencing weird issues/instability, you will know what the issue likely is. If this happens, you could return the new stick to the retailer.

You probably can also find a matched set in the FS forum here. A lot of people are dumping their DDR3 as they move to Ryzen/Kaby Lake builds, and I have seen 16 GB kits being listed around $60.

 

[Insert_Nickname]

So long as you use the frequency and timings from the slowest DIMM, you shouldn't have any issues. Lowest common denominator is key here.

A good link explaining the issue, and Intel Flexmemory:

https://www-ssl.intel.com/content/www/us/en/support/boards-and-kits/000005657.html

Flex mode
This mode results in both dual and single-channel operation across the whole of DRAM memory. The figure shows a flex mode configuration using two DIMMs. The operation is as follows:

• The 2 GB DIMM in slot 1 and the lower 2 GB of the DIMM in slot 2 operate together in dual-channel mode.
• The remaining (upper) 2 GB of the DIMM in slot 2 operates in single-channel mode.

 

[VirtualLarry]

Be aware of potential issues mixing dual-rank and single-rank modules in dual-channel.
(I think?)