What is CAS Latency?

RAM is a critical component of a PC. So, when it comes to installing the correct RAM in your computer, many factors are needed to be considered. We are all aware that RAM with more gigs of memory and higher speeds in terms of MHz performs better. But the CAS Latency or CL abbreviated is often overlooked even though it has a huge role in how efficient a RAM module is. Therefore, in this article we will discuss the meaning of RAM CAS Latency and why it matters.

CAS Latency Meaning

CAS Latency (CL) is an abbreviation for Column Address Strobe Latency. The CAS Latency is defined as the total number of clock cycles it takes from when the memory controller receives an instruction for retrieving data to the time a RAM module accesses the specific data from a particular column address and makes it available at one of its output pins. Generally, when comparing RAM from similar generations (e.g., DDR4, DDR3, etc.), a lower latency RAM will perform better.

A RAM module is responsible for receiving a command for data retrieval and then making that data available on its output pins. The process of data retrieval begins from the CPU which sends the command to the memory controller and then the memory controller sends the command to the RAM.

Upon receiving the command, the RAM module retrieves the data and sends it to its output pins. During these retrievals, for each data that is retrieved, the RAM module goes through certain cycles. These cycles are known as the RAM CAS Latency.

This means that the fewer cycles the RAM has to go through, the faster the data would be retrieved making your computer more efficient. This makes lower CAS Latency RAMS better than those having higher CAS Latencies.

If you’re still having problems understanding what CAS latency is then consider a line at the checkout counter of a grocery store. The number of lines here will represent the gigs of memory that a RAM has. The speed or frequency with which the lines are moving forward represents the clock speed of the RAM. CAS Latency is represented by everything going on at the cashier’s end. The cashier scanning your grocery items, processing your payment, and giving you the receipt is considered as one cycle. If the cashier is slow or encounters any delays, that would mean higher latency as it takes more time to complete the cycle. On the other hand, if the cashier is fast and efficient that would mean lower latency as it takes less time to complete the cycle. Therefore, the lower the CL a RAM module has the better.

Does CL matter in RAM?

Yes, CAS Latency does matter in RAM but, CL alone won’t guarantee better performance unless you factor in RAM frequency or speed into consideration. Take, for example, the CL difference between DDR4 and DDR3 RAM. While DDR3 had a minimum CL of 9, DDR4 performs significantly better with minimum CL of 14, simply because of the superior clock speeds that substantially impacted the latency in seconds.

Lower latency in seconds can show massive changes when switching generations. Still, the difference might not be significant in the same generation as the CL tends to increase with a small frequency increment. Games typically show a slight increase (1-2 fps) in performance. Where CL really matters is in configuring RAM from different manufacturers to run in dual or quad-channel configurations for more significant performance improvements.

What is the best RAM CL?

Generally, for DDR4 modules, the best CL you can get will be around 14. However, a CL of 15 or 16 is also considered really good for mid to higher-end systems.

Kits like this Corsair Vengeance LPX with a CL of 14 and frequency 3600MHz are the best performing DDR4 RAM you can get, but they cost a larger amount of money compared to high CL RAM with similar frequencies.

To get the best performance while saving money, we would recommend before making a buying decision that you identify the supported memory speeds of both your processor and motherboard. After confirming the supported frequencies, browse through different options available in the market and choose the one with the lowest CL, highest frequency, and gigs of memory that fits within your budget.

Calculating RAM Latency

The CAS Latency ratings of the RAM are usually presented with the RAM by the engineers, either on the RAM itself or on the paperwork alongside the RAM. You’ll often see the term ‘CL’ followed by a couple of digits separated by hyphens. The digits before the first hyphen represent the CAS Latency of the RAM. Let’s suppose that the digit is 17, then this means that the RAM will go through 17 cycles to deliver the data to the memory controller.

To convert this RAM Latency into nanoseconds, and for it to make actual sense you’ll have to put this number through a formula. Divide the CAS Latency by the clock speed of the RAM and then multiply it by 2000 to obtain the RAM Latency in nanoseconds.

In case you’re not aware of the CAS Latency of your RAM then there are several online tools such as CPU-Z available on the internet that you can download, and they’ll give you the required information in a single click. The clock speed of the RAM could be seen from the task manager in Windows. You can also utilize this RAM latency calculator.

RAM Speed vs. CAS Latency

The major difference between RAM Speed and CAS Latency is that the more RAM speeds the better, and the lesser the CAS Latency, the better. They are pretty much the inverse of each other. RAM speed defines the amount of data that a RAM can transfer in one second. CAS Latency on the other hand defines the number of cycles that a RAM goes through before transferring data.

Final Thoughts

RAM that has the highest clock speed and lowest CAS Latency allows for the optimum performance you so desire. Taking this information into account along with your desired storage size (8GB, 16GB, 32GB, etc…) and budget will allow you to determine which RAM is Ideal for your computer. Now you’re up to date with everything you need to know before picking up your RAM stick off the shelf.

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