Issue with DDR5 Ram

[BlueBaum271]

I have recently put my PC together outside the box for the first time and I seem to have put everything together correctly, there is one thing though. My RAM is CL46 5600, but in the BIOS the EXPO profile is set to 5200mhz, the weird thing: EXPO profile 1 is DDR 5 5600MT/s 46-45-45-90 1.100V and EXPO profile 2 is DDR 5 5200MT/s 42-42-42-105 1.100V what does that mean if the EXPO profile thats running is running at cl42 instead of cl46 (if I understand correctly cl42 is faster, but the RAM can only run at cl46 so how does that work)? 

And another thing, I can't seem to change the EXPO profile.

 

My Motherboard is a MSI MAG B650 Tomahawk Wifi and my RAM is Crucial DDR5 Pro CL46 5600

[Eigenvektor]

CL is short for CAS Latency and is measured in clock cycles, so numbers are only directly comparable at the same clock speed.

 

CL 46 at 5600 MT/s translates to (CL × 2000 / Bandwith; 46 × 2000 / 5600 =) 16.4 nanoseconds

CL 42 at 5200 MT/s is (42 × 2000 / 5200 =) 16.2 nanoseconds

 

So the difference between the two isn't that big. You have slightly lower transfer speed than you would have at 5600 MT/s, but in return you get slightly lower latency. It's completely normal for latency to increase as transfer speeds increase. Think of it as a tradeoff of sorts.

 

When you overclock RAM, it may be necessary to increase latency and/or voltage for it to run stable. The inverse is also true. As you decrease clock speeds, lower latency may be more attainable.

[WoodenMarker]

22 minutes ago, BlueBaum271 said:

RAM can only run at cl46

No. RAM can attempt to run with whatever settings are set. Advertised speeds and EXPO profiles are manufacturer validated settings that are expected to be stable. 

 

The motherboard defaults to JEDEC speeds. The advertised RAM speeds are technically an overclock and selecting either of the profiles loads those settings.

Try updating the BIOS and see if that allows you to select the EXPO profile. 

[BlueBaum271]

2 hours ago, Eigenvektor said:

CL is short for CAS Latency and is measured in clock cycles, so numbers are only directly comparable at the same clock speed.

 

CL 46 at 5600 MT/s translates to (CL × 2000 / Bandwith; 46 × 2000 / 5600 =) 16.4 nanoseconds

CL 42 at 5200 MT/s is (42 × 2000 / 5200 =) 16.2 nanoseconds

 

So the difference between the two isn't that big. You have slightly lower transfer speed than you would have at 5600 MT/s, but in return you get slightly lower latency. It's completely normal for latency to increase as transfer speeds increase. Think of it as a tradeoff of sorts.

 

When you overclock RAM, it may be necessary to increase latency and/or voltage for it to run stable. The inverse is also true. As you decrease clock speeds, lower latency may be more attainable.

Thanks for the reply! So in short I don't have to do anything and it's fine?

[Hellowpplz]

1 hour ago, BlueBaum271 said:

Thanks for the reply! So in short I don't have to do anything and it's fine?

Past choosing whichever one you prefer, no.

[Eigenvektor]

5 hours ago, BlueBaum271 said:

Thanks for the reply! So in short I don't have to do anything and it's fine?

It's fine in the sense that nothing is defective. As @WoodenMarker said, a BIOS update might get the second EXPO profile working as well.

 

5600 MT/s CL 46 would give you ~7.7% higher memory bandwidth at the cost of ~1.2% higher latency compared to 5200 MT/s CL 42. You could test with a few games if there's any measurable difference, but it'll likely be negligible. Synthetic memory benchmarks might show some difference.