Different capacity RAMs, but still in dual channel?

[NemesisPrime_691]

Hi people! I have an Acer Aspire A515-51G laptop with the following specs:

 

Intel Core i5-8250u

Nvidia GeForce MX150 2GB GDDR5

1TB WD Blue HDD

240 GB M.2 WD Green SATA SSD

4GB soldered 2400MHz + 16GB Crucial 2400MHz

 

I just installed 16GB 2400MHz RAM into the only slot in the laptop that came fitted with a 4GB module. Earlier, the 4+4 memory was running in dual channel mode, checked it via CPUz. I was afraid that me purchasing the 16GB stick would probably make the RAM run in Single channel mode, but I went ahead with the upgrade since it would have helped with my office work when I have to run multiple applications, multiple instances of Visual Studio, Chrome tabs etc.

 

However, I installed the RAM, making a total of 20GB, fired up CPUz, and low and behold, the Memory tab still shows channel # as Dual. What happened here? I read everywhere that I would have to get a same speed, same size and same latency RAMs in order to make it run in Dual channel mode, but here I just have the RAM with same frequency and latency. Then how is this still in Dual channel?

[Ben17]

5 minutes ago, SpiderGuy said:

Hi people! I have an Acer Aspire A515-51G laptop with the following specs:

 

Intel Core i5-8250u

Nvidia GeForce MX150 2GB GDDR5

1TB WD Blue HDD

240 GB M.2 WD Green SATA SSD

4GB soldered 2400MHz + 16GB Crucial 2400MHz

 

I just installed 16GB 2400MHz RAM into the only slot in the laptop that came fitted with a 4GB module. Earlier, the 4+4 memory was running in dual channel mode, checked it via CPUz. I was afraid that me purchasing the 16GB stick would probably make the RAM run in Single channel mode, but I went ahead with the upgrade since it would have helped with my office work when I have to run multiple applications, multiple instances of Visual Studio, Chrome tabs etc.

 

However, I installed the RAM, making a total of 20GB, fired up CPUz, and low and behold, the Memory tab still shows channel # as Dual. What happened here? I read everywhere that I would have to get a same speed, same size and same latency RAMs in order to make it run in Dual channel mode, but here I just have the RAM with same frequency and latency. Then how is this still in Dual channel?

 

You can still run dual channel with mismatched memory it just won't necessarily perform as well as matched memory.

I used  to have 6GB mismatched memory in a old Pentium prebuilt i used to have till it broke (a 4 GB hp ddr3 module and a 2 GB Kingston module (same frequency i think )

[Sakkura]

The first 4GB of the 16GB stick are being matched with the 4GB stick. So you have 8GB of memory in dual channel, the rest in single channel.

[mariushm]

Some processors support a sort of "hybrid" mode, where the capacity that's common works in dual channel mode (so you have 4+4 or 8 GB in dual channel mode) and the rest (12 GB) works as if it's in single channel mode.

When reading or writing to that portion above 8 GB, you'd get slower speeds but it will function.

 

Old systems (think dual channel with DDR2 times) had problems with dual channel with different capacities. They added support for these "hybrid" dual channel modes quite a long time ago. It's a bit fuzzy but I remember reading about such features in G41 (socket 775) chipsets from Intel and AMD had similar features around that time as well.

 

[NemesisPrime_691]

6 minutes ago, Sakkura said:

The first 4GB of the 16GB stick are being matched with the 4GB stick. So you have 8GB of memory in dual channel, the rest in single channel.

 

4 minutes ago, mariushm said:

Some processors support a sort of "hybrid" mode, where the capacity that's common works in dual channel mode (so you have 4+4 or 8 GB in dual channel mode) and the rest (12 GB) works as if it's in single channel mode.

When reading or writing to that portion above 8 GB, you'd get slower speeds but it will function.

 

Old systems (think dual channel with DDR2 times) had problems with dual channel with different capacities. They added support for these "hybrid" dual channel modes quite a long time ago. It's a bit fuzzy but I remember reading about such features in G41 (socket 775) chipsets from Intel and AMD had similar features around that time as well.

 

That's pretty neat. This is the first time I am learning of this. Thanks for the explanation!

 

I was also wondering, would it be a big difference between the performance of 8GB dual channel and 12GB single channel?

[mariushm]

It depends on what you use the memory for.

If you have integrated graphics that uses the RAM, then dual channel will give you better performance in games even though the capacity is smaller.

 

If you often use applications that use more near or more than 8 GB of memory, like Google Chrome for example, then 12 GB in single channel may make more sense.  Chrome is the kind of application which deals with lots of SMALL chunks of data (small images, pages, javascript code in pages etc), and generally these files are too small for the benefits of dual channel memory to kick in and make a noticeable improvement.

 

But, even this is debatable... if you have a SSD in the system, often it's just overall better to have dual channel memory and less memory because the operating system can use the SSD for swapping unused data from memory onto the SSD.