Can two different sized RAM run in dual channel?

[Ariando]

Hi, I'm a newbie in PC building. I'm in the process of building my first budget PC for gaming and editing. I accidentally bought a single stick of RAM (16 gigs, 2666 mhz) instead of 2 x 8 gigs configuration. My question is, if I buy another stick with the same speed but different size (say, 4 gigs 2666 mhz) and put it alongside the 16 gigs RAM, can they run in a dual channel manner ? Also, will it be safe ? Thanks in advance!

[duckypath]

I feel as if the issues brought about from mixing very different ram sizes, speeds, brands, etc outweigh the speed of single channel memory provide. I'd say either return and get 2x8, or stick with the 1 16gb and upgrade later.

[GhostRoadieBL]

In dual channel the system will be unstable, dual channel writes (and reads) from both sticks at the same time. Kind of like raid0 for memory, with different sized sticks system crashes when you write past the 4gb on both sticks. You can run single channel mixed sizes with no issues 

[Ariando]

4 minutes ago, duckypath said:

I feel as if the issues brought about from mixing very different ram sizes, speeds, brands, etc outweigh the speed of single channel memory provide. I'd say either return and get 2x8, or stick with the 1 16gb and upgrade later.

Thanks for the info. I too feel like it's too risky to do. Unfortunately for me returning it is no longer an option. Guess I'm just going to try to sell it to someone else at a little loss.

[steelo]

Won't it run in dual channel at whatever speed the slower RAM is running? I've always been confused about this.

[CADGuy23]

It can work but you also run the risk of having issues.  I've run 8gb and 4gb sticks and similarly 512mb and 1gb stick together with no issues. 

 

If it's a new build, you should try and return the chip and buy the 2x8 set.

[Ariando]

3 minutes ago, GhostRoadieBL said:

In dual channel the system will be unstable, dual channel writes (and reads) from both sticks at the same time. Kind of like raid0 for memory, with different sized sticks system crashes when you write past the 4gb on both sticks. You can run single channel mixed sizes with no issues 

Thanks for the insight. I had no idea about that. Learned something new today.

[TehDwonz]

1 minute ago, steelo said:

Won't it run in dual channel at whatever speed the slower RAM is running? I've always been confused about this.

It's down to the specific motherboard and BIOS. Some allow it, some don't. It's not recommended, but if it's all you have available, it should at least function.

[steelo]

Just now, TehDwonz said:

It's down to the specific motherboard and BIOS. Some allow it, some don't. It's not recommended, but if it's all you have available, it should at least function.

Gotcha, I had a similar scenario a few weeks ago where I wanted to upgrade 8gb to 16gb but the memory wasn't available. I opted to just buy all new RAM.

[SpaceGhostC2C]

 

20 minutes ago, Ariando said:

 My question is, if I buy another stick with the same speed but different size (say, 4 gigs 2666 mhz) and put it alongside the 16 gigs RAM, can they run in a dual channel manner ? 

If inserted in the right slots, they will run  partially in dual channel mode. In your example, you will have 8GB in dual channel mode (4gB+4GB), while the excess 12GB of the original stick will work in single channel mode.

[Ariando]

1 minute ago, SpaceGhostC2C said:

 

If inserted in the right slots, they will run  partially in dual channel mode. In your example, you will have 8GB in dual channel mode (4gB+4GB), while the excess 12GB of the original stick will work in single channel mode.

If that so, will the issue that @GhostRoadieBL mentioned happen if the RAM usage got over 8 GB ?

[SpaceGhostC2C]

2 minutes ago, Ariando said:

If that so, will the issue that @GhostRoadieBL mentioned happen if the RAM usage got over 8 GB ?

I've never heard of that issue. Whenever I encountered such size mismatched, it worked as I described.

However, you can find the answer to  your particular case in your motherboard's manual. In the RAM installation section, it should detail how different combinations of RAM modules will work, and where to install them to that end.

[GhostRoadieBL]

2 minutes ago, WikiForce said:

not unstable but dual channel will not work properly for sure, i had 6gb ram back in the day (4+2) and it had zero issues but there did seem performance issues as certain games would stutter and run smootherwith only one 4gb stick. It just won't run dual channel above the capacity of smaller capacity ram stick and in most cases performance difference is negligible except if you're running ryzen which gets decent boost from high frequency and proper dual channel

My older x58 system would cause all kinds of havoc with mixed size sticks but that might have been a legacy triple channel quirk they solved with more recent dual channel 

 

[GhostRoadieBL]

11 minutes ago, Ariando said:

If that so, will the issue that @GhostRoadieBL mentioned happen if the RAM usage got over 8 GB ?

It seems I'm running on old info, newer systems will still be stable but run in single channel after the 8gb is filled. 

Average day to day it shouldn't be noticeable, only gaming or heavier workloads like editing or rendering would slow it down to single stick speed (which you have now) 

[Ariando]

4 minutes ago, SpaceGhostC2C said:

I've never heard of that issue. Whenever I encountered such size mismatched, it worked as I described.

However, you can find the answer to  your particular case in your motherboard's manual. In the RAM installation section, it should detail how different combinations of RAM modules will work, and where to install them to that end.

Got you. My motherboard (Asrock b460m pro4) manual says I need to install identical (the same brand, speed, SIZE, and chip-type) ddr4 DIMM pairs for dual channel to work. Guess I'm just going to sell that 16 gigs stick because returning it is no longer an option now unfortunately 

[Tristerin]

31 minutes ago, SpaceGhostC2C said:

 

If inserted in the right slots, they will run  partially in dual channel mode. In your example, you will have 8GB in dual channel mode (4gB+4GB), while the excess 12GB of the original stick will work in single channel mode.

Didn't read everything, but @SpaceGhostC2C has it right