[SOLVED] Why the 4 RAM slots?

[GavriloJm]

Hi guys,

Some years ago I built my pc and it has the B150M Bazooka motherboard. This mobo supports only 2 RAM slots, I believe, but it has 4 slots (2 black, 2 grey). I currently have 2x4gb RAM and I'm looking to upgrade to 16gb. But if it can only support two slots, why does it have 4? And what happens if I put 2x8gb in the 'best' slots and 2x4gb in the other 2 (same type of RAM considering brand etc, just the 2x8gb version)?

Thanks for your time!

 

[JohnBonhamsGhost]

This mobo supports only 2 RAM slots,

it supports "dual channel" memory,
not just two DIMM slots.

what happens if I put 2x8gb in the 'best' slots and 2x4gb in the other 2 (same type of RAM considering brand etc, just the 2x8gb version)?

it is never recommended to mix RAM sticks from different sets
even if they are the exact same make\model\speed\timings.
packaged sets are thoroughly tested to work together.
you never know if mixing sets will lead to errors, crashes, or just a loss of possible speed & functionality due to the difference.

many will claim that they have done it and found no issues,
but there is still a possibility even with these circumstances that they have actually lost some functionality.
many more have shown that their mixed sets have led to much more noticeable system problems.

 

[thx1138v2]

Hi guys,

Some years ago I built my pc and it has the B150M Bazooka motherboard. This mobo supports only 2 RAM slots, I believe, but it has 4 slots (2 black, 2 grey). I currently have 2x4gb RAM and I'm looking to upgrade to 16gb. But if it can only support two slots, why does it have 4? And what happens if I put 2x8gb in the 'best' slots and 2x4gb in the other 2 (same type of RAM considering brand etc, just the 2x8gb version)?

Thanks for your time!

"This mobo supports only 2 RAM slots, I believe, ". This is incorrect. It supports all 4 slots but in 2 sets of dual channel memory.

It would be a bad idea, however, to attempt to add memory modules to your existing memory because they are not always compatible when adding to an existing system. If you do this they may work together and they may not. They might run in single channel mode or they may not run at all. As long as you buy the RAM modules in a matched set they will work together but if you mix them with other RAM the outcome is unpredictable.

Each module is 64 bit wide, meaning data transfers to and from memory happen 64 bits at a time. The "dual channel" feature makes them appear to the memory controller to be twice as wide so the data transfers happen 128 bits at a time. So your system will, if you populate all of the sockets, have 2 sets of dual channel RAM.

Your best bet is to buy two 8Gb RAM modules and run only those in the same sockets you are using now for the 4Gb RAM modules.

 

[GavriloJm]

it supports "dual channel" memory,
not just two DIMM slots.

Yes, I meant two at the same time. It doesn't do more at the same time right?

it is never recommended to mix RAM sticks from different sets
even if they are the exact same make\model\speed\timings.
packaged sets are thoroughly tested to work together.
you never know if mixing sets will lead to errors, crashes, or just a loss of possible speed & functionality due to the difference.

many will claim that they have done it and found no issues,
but there is still a possibility even with these circumstances that they have actually lost some functionality.
many more have shown that their mixed sets have led to much more noticeable system problems.

Thanks, I already ordered the 2x8gb, so I guess I'll just stick with those then. Should be plenty for gaming anyways

 

[JohnBonhamsGhost]

Yes, I meant two at the same time. It doesn't do more at the same time right?

Yes it does. But, both sets would be running in dual-channel mode instead of a possible quad-channel.

 

[GavriloJm]

Yes it does. But, both sets would be running in dual-channel mode instead of a possible quad-channel.

Ah okay, thanks for your help!

 

[hotaru.hino]

Yes, I meant two at the same time. It doesn't do more at the same time right?

A benefit to populating all four slots is that the CPU can interleave memory operations between one set of two modules and the other. So the CPU can issue a read on one set and while that's going on, issue a read on another set and when it comes back to the first set, the contents should be ready. Though I'm not sure how much benefit this actually has in practice.