Cl value for ram?

archz2 · 06 May 2023

I recently bought a laptop with 4800Mhz installed RAM of DDR5 make. There are two sticks of 8GB each. It supports upgrade to a total of 64 GB. The laptop has in total of two slots for RAM. I'll remove the current RAM sticks.

I am doing market survey for different RAMs. I came across a term called CL value. Upon looking up in cpuz, I get this. Where exactly is the precise CL value of my RAM is given?

As of now I have come across RAMS having the value of 38 or 40. If the current RAMS in my machine have CL 40 value and if I install two RAMS of CL 38 value, will it be okay or do I need to get CL 40 RAM only?

Ghot · 06 May 2023

archz2 said:

I recently bought a laptop with 4800Mhz installed RAM of DDR5 make. There are two sticks of 8GB each. It supports upgrade to a total of 64 GB. The laptop has in total of two slots for RAM. I'll remove the current RAM sticks.

I am doing market survey for different RAMs. I came across a term called CL value. Upon looking up in cpuz, I get this. Where exactly is the precise CL value of my RAM is given?

As of now I have come across RAMS having the value of 38 or 40. If the current RAMS in my machine have CL 40 value and if I install two RAMS of CL 38 value, will it be okay or do I need to get CL 40 RAM only?

CL or CAS Latency is like the 0 to 60 times on a car. It's how fast the RAM can do it's thing. It's "latency".
Two numbers affect the overall speed of the RAM. The CAS Latency and the frequency.

In other words, 4800Mhz RAM with a CAS Latency of 40, is faster than 4800Mhz RAM with a CAS Latency of 42.
This is also true for the "other" RAM "timings". The lower the numbers, the better (faster).

This is why RAM stick with the same frequency, but lower timing numbers, cost more.
CL 16 RAM will cost more than CL 19 RAM, assuming the same frequency.

The computer doesn't limit the CAS Latency... the RAM stick does.
When they manufacture RAM, they aim for the highest frequency, with the lowest timings.
After the RAM is manufactured, they test it, and sort it by frequency and timings. It's called binning.
(Like sorting things into... bins).

In CPU-Z, the column on the far right shows the fastest un-overclocked speed and timings the RAM stick can handle. These speed and timings are limited my the RAM stick, not by the computer.

As mentioned above, the RAM sticks with the highest frequency and lowest timings, will cost the most, cause they are like a... big block Ford (high frequency), with killer 0 to 60 times (lower latency).

NOTE: The other "hardware" in the computer, namely the CPU and the RAM slots on the motherboard, have their own limits. CPUs have an Integrated Memory Controller (IMC) and the RAM slots (motherboard) will have it's "recommended" frequency and amount, in GB of RAM that the slot will support.

This info can be found in the CPU specs, and in the motherboard specs.
If you're using a RAM manufacturer's compatibility tool... the CPU and motherboard limitations will be taken into account.

Now laptops are a bit different...

For a laptop, these limits will be listed in the laptop specs. Like it might say... this laptop only supports 16GB of RAM in each slot. And when I Google your CPU, I find the fastest frequency (un-overclocked), RAM that the CPU will support.

Intel(R) Core™ i7-8750H Processor

As for the maximum amount of RAM (64GB). The information "?" says: Maximum amount of RAM the CPU will support. If you look up the laptop specs on the ACER website, it will usually say... so many GB per slot.

In other words... the CPU may support 64GB of RAM, but the motherboard in your laptop may only support 32GB per slot (for two slots), or 16GB per slot for four slots.

In short... CAS Latency limits are NOT determined by the motherboard or CPU... just by your wallet.

Explaining RAM sure takes a lot of typing. LOL

Helmut · 06 May 2023

Cutting to the chase, the SPD Tab is the JEDEC profiles for timings. i.e. pre-set profiles of the particular memory modules. It is not showing the first 4 profiles.
The Memory Tab will show the actual timings used and that will correspond to one of those profiles.

My Laptop uses exactly the same Samsung memory DDR5 SODIMM modules and it uses the JEDEC #7 profile CL40.
This is at 1.1v

The CL38 modules maybe at a higher voltage and be XMP profiles at 1.25v which means they will run hotter, not good on a Laptop, it may not be capable of using XMP profiles either.

You do not want to over buy on memory modules as the Laptop may not use the CL38 anyway.

DDR5 memory modules are thought to be continuing to decrease in price this year, so there is no hurry.

archz2 · 06 May 2023

Ghot said:

CL or CAS Latency is like the 0 to 60 times on a car. It's how fast the RAM can do it's thing. It's "latency".
Two numbers affect the overall speed of the RAM. The CAS Latency and the frequency.

In other words, 4800Mhz RAM with a CAS Latency of 40, is faster than 4800Mhz RAM with a CAS Latency of 42.
This is also true for the "other" RAM "timings". The lower the numbers, the better (faster).

This is why RAM stick with the same frequency, but lower timing numbers, cost more.
CL 16 RAM will cost more than CL 19 RAM, assuming the same frequency.

The computer doesn't limit the CAS Latency... the RAM stick does.
When they manufacture RAM, they aim for the highest frequency, with the lowest timings.
After the RAM is manufactured, they test it, and sort it by frequency and timings. It's called binning.
(Like sorting things into... bins).

In CPU-Z, the column on the far right shows the fastest un-overclocked speed and timings the RAM stick can handle. These speed and timings are limited my the RAM stick, not by the computer.

As mentioned above, the RAM sticks with the highest frequency and lowest timings, will cost the most, cause they are like a... big block Ford (high frequency), with killer 0 to 60 times (lower latency).

NOTE: The other "hardware" in the computer, namely the CPU and the RAM slots on the motherboard, have their own limits. CPUs have an Integrated Memory Controller (IMC) and the RAM slots (motherboard) will have it's "recommended" frequency and amount, in GB of RAM that the slot will support.

This info can be found in the CPU specs, and in the motherboard specs.
If you're using a RAM manufacturer's compatibility tool... the CPU and motherboard limitations will be taken into account.

Now laptops are a bit different...

For a laptop, these limits will be listed in the laptop specs. Like it might say... this laptop only supports 16GB of RAM in each slot. And when I Google your CPU, I find the fastest frequency (un-overclocked), RAM that the CPU will support.

Intel(R) Core™ i7-8750H Processor

As for the maximum amount of RAM (64GB). The information "?" says: Maximum amount of RAM the CPU will support. If you look up the laptop specs on the ACER website, it will usually say... so many GB per slot.

In other words... the CPU may support 64GB of RAM, but the motherboard in your laptop may only support 32GB per slot (for two slots), or 16GB per slot for four slots.

In short... CAS Latency limits are NOT determined by the motherboard or CPU... just by your wallet.

Explaining RAM sure takes a lot of typing. LOL

Wow. Thanks a lot for such a detailed and clear explanation!

- - - Updated - - -

Helmut said:

You do not want to over buy on memory modules as the Laptop may not use the CL38 anyway.

DDR5 memory modules are thought to be continuing to decrease in price this year, so there is no hurry.

Actually I bought a 1TB SSD also. I checked with the service center. They won't charge money for upgrades. So I thought, get all the upgrades done once and for all. Hehe.

bro67 · 06 May 2023

You are doing a whole lot of work when companies like Crucial and the laptop mfg. have already done the hard work. Just purchase from Crucial like millions of others have done. Also just because the motherboard can see 64gb does not mean that you are going to need 64gb for every day use.