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

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  • Post last modified:October 13, 2020
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3 Ways to find Accurate CAS Latency (CL) Ratio of RAM

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

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

If you have better information about the CAS latency ratio, then navigate toward methods to find out CAS latency ratio.

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

CAS ➔ Column Address Strobe

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

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

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

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

What is CAS Latency (CL) Ratio?

Now, it’s obvious to have doubt that who is requesting the data to RAM. Right?

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

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

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

In above illustration, Manager asking the salesman for box which contains 3 mangoes. After searching for 2 minutes, the sales concluded that the box ‘C’ contains the 3 mangoes.

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

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

cas cl ratio illustration

In above illustration the CAS Latency Ratio is 16.

  • As you may aware CPU processor is the brain of computer.
  • It processes the datasets supplied by cache memory, known as L1, L2 & L3 cache.
  • When required dataset not available with these caches then the processor orders to memory controller to fetch that dataset from RAM.
  • Memory controller works as the middleman between processor and RAM.
  • Now memory controller forwards this request to RAM.
  • RAM processes’ the request and produce the output to 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 nano seconds for asynchronous DRAM. Whereas for synchronous DRAM, the CL ratio specified in clock cycles.

Right now, few doubts might come in your mind. Some of them 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 same clock speed (i.e. 3200 MHz x 2 RAM)

Can you mix CAS latency RAM?

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

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

For example, you have installer two RAM modules with CL ratio 15 & 16. Then motherboard will set CL ratio 16 for both RAM. Indirectly, low latency RAM will be degraded to match with higher latency ratio of another RAM.

What is a good CAS latency for RAM?

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

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

Sametime, its recommended to do not mix RAM with different clock speed or different CL ratio. Otherwise, such RAM modules will not be able to work at their specified speed.

For example, we have two RAM modules with following specification.

RAM ModuleClock SpeedCL Ratio
A2600 MHz17
B2600 MHz15

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

How do I check my CAS latency?

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

Method A: via CPU-Z

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

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

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

Be careful with about DRAM Frequency and Clock Speed, which may confuse you while a selection of RAM. If you are Windows 8 or 8.1 users, then you can easily find out clock speed. It is located under Task Manager (Press Ctrl + Shift + Esc) > Performance > Memory. Alternatively, visit a Wikipedia to find out clock speed when you know the DRAM Frequency or Command Rate.

Moreover, the SPD tab  in CPU-Z reveals detailed report of your RAM. Alternatively, you can Google for the current part number and manufacturer to dig exact information about your current RAM. It may be helpful to predict the second RAM. It’s better to choose the RAM from the same manufacturer for utmost compatibility. Hope this information will help to 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 of 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 navigate to RAM section. Now you can view Slot information, type, size, CL ratio and much more. See the following screengrab.

CAS latency

Method C: via Command Prompt / DOS / PowerShell

In some cases, installing new software is not permissible due to the administrator’s restriction. Or user unable to enter GUI mode (computer restarting in DOS mode). So, 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 Run window. Write CMD press OK
      or
    2. Click Start button & type CMD press Enter
  2. Type following command
    wmic memorychip get manufacturer, capacity, part number, speed, memory type, device locator, formfactor 
  3. It will show information about 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

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

This Post Has 2 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.

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