3 Ways to Find Accurate CAS Latency (CL) Ratio of RAM

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  • Post last modified:October 20, 2023
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You are currently viewing 3 Ways to Find Accurate CAS Latency (CL) Ratio of RAM

Are you one of those who searched a lot about the CAS Latency (CL) ratio? Still unsure about the exact meaning & where to locate it? Don’t worry, we will try our best to explain it.

CL Ratio is crucial when purchasing add-on RAM. It plays a significant role when upgrading or replacing current RAM modules. RAM with different CL numbers can hinder achieving optimal performance.

If you need better information about CAS latency ratio, then navigate towards methods to find out CAS latency ratio.

Before diving into the definition, let us see what the full form of the CAS is.

CAS ➔ Column Address Strobe

I bet; you may still be skeptical about the CAS latency ratio. Since the full form does not reveal any understandable meaning.

Don’t worry, why are we here? We are doubt solvers. ? Let’s look at the CAS latency ratio step by step.

  • CAS latency (CL) can be defined as the time gap between the read command initiated by the memory controller and the moment when data is made available by the RAM.
  • Simply, it’s delayed to produce data by a column of RAM.

Thus, a lower CAS latency ratio denotes better performance. However, not only the CAS latency ratio but the clock speed, rank, DDR generation, ability to overclock and other factors are crucial while predicting performance. That’s why Doubt Solver recommends using RAM with the same CL ratio & same clock speed for optimum performance.

What is the CAS Latency (CL) Ratio?

Now, it’s obvious to have doubts about who is requesting the data for RAM. Right?

I know it’s still beyond understanding, especially for non-technical guys.

Before jumping into this technical arena, let me tell a non-technical story.

cas cl ratio non technical illustration
Non-technical illustration for a better understanding of CL Ratio

In the above illustration, the Manager asks the salesman for a box that contains 3 mangoes. After searching for 2 minutes, the salesman concluded that box ‘C’ contained 3 mangoes.

In the above illustration, the time gap is 2 minutes (i.e., time taken to process the request). So, these 2 minutes are nothing but the CAS latency ratio of our illustration.

Now, let’s apply the above illustration to real life scenarios.

cas cl ratio illustration
Technical illustration for a better understanding of CL Ratio

In the above illustration, the CAS Latency Ratio is 16.

  • As you may be aware, the CPU processor is the brain of the computer.
  • It processes the datasets supplied by cache memory, known as L1, L2 & L3 cache.
  • If the required dataset is not available with these caches then the processor orders the memory controller to fetch that dataset from RAM.
  • The memory controller works as the middleman between the processor and RAM.
  • The memory controller forwards this request to RAM.
  • RAM processes the request and produces the output to the memory controller.
  • This delay between requesting & receiving the dataset is nothing but the CAS latency or CL ratio of that RAM.

CL ratio specified in nanoseconds for asynchronous DRAM. Whereas for synchronous DRAM, the CL ratio is specified in clock cycles.

Right now, a few doubts might come to mind. Some of them are discussed below.

Is a higher or lower CAS latency better?

Lower CAS Latency Ratio is always better than higher CAS Latency Ratio.

Assuming you are choosing multiple RAM with the same clock speed (i.e., 3200 MHz x 2 RAM)

Can you mix CAS latency RAM?

Although NOT recommended; technically you can mix different CAS latency RAM modules.

However, the motherboard will match the CAS latency ratio by setting a higher CAS ratio among the installed RAM modules.

For example, you have installed two RAM modules with CL ratios 15 & 16. The motherboard will set a CL ratio of 16 for both RAMs. Indirectly, low-latency RAM will be degraded to match the higher latency ratio of another RAM.

What is a good CAS latency for RAM?

The performance of the RAM module depends on multiple factors. Such as clock speed, latency ratio, rank, etc. So, merely judging RAM on the basis of the CAS latency (CL) ratio is not right.

Remember, RAM with a lower CAS latency ratio is always better than a higher one. Lower latency assures the processing of data in minimal time.

Sometimes, it’s recommended to not mix RAM with different clock speeds or different CL ratios. Otherwise, such RAM modules will not be able to work at their specified speed.

For example, we have two RAM modules with the following specifications.

RAM ModuleClock SpeedCL Ratio
A2600 MHz17
B2600 MHz15
Comparing CL Ratios

Which of these would you choose? Right, as per our theory, we will go with a lower CL ratio RAM. Here, RAM module B is faster than A. A lower CL ratio is better.

How do I check my CAS latency?

Here we are giving three methods to find out the exact CAS latency (CL) ratios of memory modules.

Method A: via CPU-Z

Follow the below steps to find out the CAS Latency (CL) Ratio.

  1. Download the CPU-Z application from cpuid.com
  2. Open the app and navigate to the Memory tab
  3. Read the text in front of CAS# Latency (CL)
  4. Done…!
CAS (CL) Ratio CPU-Z

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If that CAS#Latency (CL) is 9.0 clocks then your system is currently running on RAM with CL9 Ratio. This means if you want to upgrade the total RAM size without replacing the existing RAM, then you must purchase another RAM with the same CL ratio and clock speed.

How to find the clock speed of RAM?

Clock Speed (i.e., 3200 MHz) is also known as DRAM frequency or RAM speed. If you are a Windows 8, 8.1 or 10 user, then you can easily find the clock speed of your RAM without using any utility using the below method

  • Open Task Manager (Shortcut key: Ctrl + Shift + Esc)
  • PerformanceMemory.
ram clock speed task manager
Locating RAM Clock Speed under Task Manager

Moreover, the SPD tab in CPU-Z reveals a detailed report of your RAM. Alternatively, you can Google for the current part number and manufacturer to dig up exact information about your current RAM. It may be helpful to predict the second RAM. Better to choose RAM from the same manufacturer for utmost compatibility. Hope this information will help you purchase your next RAM.

Method B: via Piriform Speccy

Piriform Speccy is another good utility to fetch out CL Ratio. It also reveals tons of information about your device. It could show live uses graphs and temperatures of various components. You can export those details as XML, text file, or print / PDF. Just open the app and navigate to the RAM section. Now, you can view Slot information, type, size, CL ratio, and much more. See the following screengrab.

CAS latency
Piriform Speccy

Method C: via Command Prompt / DOS

In some cases, installing new software is not permissible due to the administrator’s restriction. or the user is unable to enter GUI mode (computer restarting in DOS mode). We are writing a solution for you. Thanks to Fazlul Haque, whose comment inspired us to update this post.

  1. Open Command Prompt
    1. Press Start + R to open the “Run” window. Write CMD press OK
    2. Click on the Start button & type CMD press Enter
  2. Type the following command
    wmic memorychip get manufacturer, capacity, partnumber, speed, memorytype, devicelocator, formfactor 
  3. It will show information about the installed RAM. Like a manufacturer, part number, speed (MHz), device locator (slot), capacity (in bytes), etc.
  4. Now, you have to copy a part number and Google it & get latency ratio information on the manufacturer’s site or shopping sites.

cas latency ratio command prompt dos
Command Prompt / DOS

Method D: via Inspecting RAM

kingston ram cl ratio
Laptop RAM

Sometimes the PC / laptop does not turn on. So, the question arises of how to know this CL ratio. At this moment you can do a solution. That is, seeing the information on the RAM itself. This process is simpler if you have a desktop computer. But laptop users have to work a little harder. However, dissembling the laptop is relatively tricky, especially for non-techies.

Anyway, once you notice the pasted sticker of a RAM, you can search for information like brand name, serial number, and model name on Google.

Once the printed serial number matches with a searched model number then you can easily access the information. We recommend viewing the information from the official website of the manufacturer. It will assure accuracy regarding specifications.

I hope this post will be helpful for you, to find the compatible RAM. Kindly comment on your doubts and suggestions. Or just convey thank you if the above solution worked for you.

This Post Has 7 Comments

  1. fazlul haque

    How can I check RAM CAS Latency using cmd in windows ?

    1. Lucky Bhumkar

      Hi Fazlul Haque, I have updated the post to solve your doubt. Thank you.

  2. Ali

    Thank you so much, it helped me a lot

  3. Baris YILMAZ

    Thank you for this usefull and user friendly usable tips. Very good job. Thx a lot…

  4. Sumit

    CPU Z shows CAS Latency CL = 10 clocks. But websites mention CL = 17 for same part number. What to do ?

  5. JC

    wmic memorychip get manufacturer,capacity,partnumber,speed,memorytype,devicelocator


  6. Anakkentang

    Is there a way to read the exact clock speed of ram with occupied 2 slot? I’ve tried CPU-Z and Speccy. Or it’s really normal for 2 occupied slots?

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