GuidesWikiWhat is CAS Latency?

What is CAS Latency? [Definitive Guide]

CAS latency refers to the duration it takes for RAM to fulfill a data access request initiated by the CPU.

Expert Verified By

Along with frequency, there is another factor that affects a RAM’s performance, and that is RAM timing. When it comes to RAM timing, there are different latencies involved, four to be precise; however, Column Address Strobe (CAS) latency is the most common RAM timing parameter. Consequently, it also has the biggest impact on the overall performance of your RAM. 

Often abbreviated as CL on RAM modules, we will learn everything there is to know about CAS latency in this guide.

Key Takeaways

  • CAS latency refers to the duration it takes for RAM to fulfill a data access request initiated by the CPU.
  • You can check CAS latency by installing system information applications, and BIOS/UEFI settings.
  • Using RAM modules with varying CAS latencies may compromise system stability, performance, and compatibility.

What Is CAS latency?

Block-Diagram-of-the-Latency-Model
Block Diagram of the Latency Model – Image Credit (Research Gate)

CAS latency is the time it takes for RAM to make the data available for use requested by the CPU. It is usually expressed in terms of the number of clock cycles, with a lower value indicating faster performance.[1] For example, CL16 indicates that the CAS latency is 16 clock cycles i.e., it takes 16 clock cycles for the RAM to provide the data requested by the memory controller.

How Does CAS Latency Impact Performance?

A RAM module with a lower CL latency can quickly respond to the memory controller’s request, resulting in faster system performance.[1] However, it’s worth noting that choosing memory modules with lower CL latency may also increase the cost of the RAM modules. It’s also important to consider other factors, such as operating voltage, clock speed, and other timing parameters, which can also affect the overall performance.[2]

How To Check CAS Latency?

Method-1: System Information Tools

While there are several ways of checking the CAS latency of your RAM module, the easier one is just installing some system information application like CPU-Z that will tell you CL latency as well as other timing parameters (e.g., tRCD, tRP, and tRAS) of your RAM.[3]

CAS latency - CPU-Z
CAS latency – CPU-Z (Image By Tech4Gamers)

Method-2: Entering BIOS/UEFI Settings

Another method is to enter the BIOS/UEFI settings of your system and look for the “Memory” or “DRAM configuration” section, where you can find RAM timings, including CL latency. However, the exact location of these settings may vary depending on the motherboard’s manufacturer, and some systems may not allow editing of RAM parameters.

CAS Latency Vs. RAM Frequency

RAM frequency, also termed RAM clock speed or simply memory speed, is the maximum frequency at which the RAM can operate. It determines how quickly data can be transferred between the memory and the processor.

Higher RAM frequencies mean faster data transfer rates and improved system performance, as the CPU can access data from the RAM more quickly. Whereas CL latency refers to the delay in data retrieval by the memory. Lower CAS latency means less delay in data retrieval and hence faster performance.[1]

It’s important to note that CAS latency and RAM frequency are interrelated, and changing one can affect the other. Higher RAM frequencies may require higher CAS latency values to maintain stability, while lower CAS latency values may require lower RAM frequencies to prevent data errors.

What Is a Good CAS Latency?

Kingston FURY RENEGADE 32GB 6400MHz CL32 - Featured
Kingston FURY RENEGADE 32GB 6400MHz CL32 (Image Captured by Us/Tech4Gamers)

Good CL latency values depend upon the type of RAM. DDR4 RAM modules are generally available with CAS latency values in the range of CL14 to CL18, which are considered good. CL14 is considered an excellent CAS latency for DDR4 memory, while other CAS latencies in the range of CL15 and CL18 are also common in DDR4 RAM modules providing good performance for most gaming needs. Where lower CL latency RAM modules can provide faster performance, they also cost more.

The CL latencies for DDR5 RAM are generally in the range of CL30 to CL40. With latency between CL30 to CL36 being the go-to choice for most gamers. While at first glance, the DDR5 RAM modules may be slower than the DDR4 modules because of their high latency, this is not the case. DDR5 memory modules may have a higher CL latency than DDR4, but they also have greater clock speed as compared to DDR4 modules.[4] The higher clock speed compensates for the high CAS Latency in DDR5 RAM.  

Can I Use RAM Modules With Different CAS Latencies On My PC?

While it is technically possible to use RAM modules with different CAS latencies in your motherboard, it is generally not recommended. Mixing RAM modules with different CAS latencies can compromise system stability, performance, and compatibility.[5] 

RAM modules operate with synchronization according to their timings. Hence, mixing RAM modules with different CAS latencies can result in timing conflicts that can lead to instability issues such as crashes, freezes, data corruption, or failure to boot.

Apart from that, it is also possible that your system will adjust the different RAM timings to the slowest one. This means that all the RAM modules will operate with the latency of the slowest RAM module, resulting in compromised performance.

More Helpful Resources By Tech4Gamers:

References:

  1. eTutorials.org. CAS Latency. Retrieved from https://etutorials.org/Misc/pc+hardware/Chapter+5.+Memory/5.3+CAS+Latency/
  2. Tech4Gamers. CPU Clock Speed: Definition & Everything To Know. Retrieved from https://tech4gamers.com/cpu-clock-speed/
  3. LinuxQuestions.org. Get the information about RAM. Retrieved from https://www.linuxquestions.org/questions/linux-software-2/get-the-information-about-ram-4175603592/
  4. Tech4Gamers. DDR4 Vs DDR5 Ram: Full Comparison [2024]. Retrieved from https://tech4gamers.com/ddr4-vs-ddr5-ram/
  5. Tech4Gamers. Can You Mix RAM Brands, Sticks, & Types? Retrieved from https://tech4gamers.com/can-you-mix-ram-brands-sticks-types/

FAQs

Is lower CAS latency better?

Yes, a lower CAS latency means faster performance. Hence, lower CAS latency is better for your PC.

Does CAS latency matter?

Yes, CAS latency does matter, as lower values indicate faster memory access times and potentially better performance.

Should I always choose the lowest CAS latency for my system?

Not necessarily, as there are many other factors along with CAS latency that will impact your system performance.

Was our article helpful? 👨‍💻

Thank you! Please share your positive feedback. 🔋

How could we improve this post? Please Help us. 😔

Related articles

Is Higher RAM Speed Always Better For Gaming? Here’s What I Think

Do you actually need a RAM as fast as 8000 MHz in 2024? Here is whether you should upgrade to a faster RAM for gaming.

Wear Leveling: Explanation & Types

The wear-levelling technique, as apparent by name, evenly distributes the data across all the memory cells of NAND flash memory so that no single cell wears out faster than others.

TLC (Triple-Level Cell): A Breakdown

TLC or Triple-Level Cell is a type of NAND flash memory used in various storage devices like SSDs and stores up to three bits of data per cell.

MLC (Multi-Level Cell): All You Need To Know

MLC or Multi-Level Cell is a type of NAND flash memory that can store two bits of data per cell and is utilized in various electronic devices.

IOPS: Guide To SSD Performance

IOPS is a metric that measures how quickly a storage device can perform read and write operations per second.

Similar Guides