Last Updated on January 31, 2021
Latency is a factor that’s just as significant as clock speed and size for a RAM. You might be missing this important aspect especially when upgrading or replacing RAM modules.
Here we talk about what is good RAM latency and why it would help you to choose the right memory for your computer.
As there are two parameters regarding RAM latency (CAS latency and true latency), a low value for both indicates a good latency. Low latency memory should be considered among RAM options with identical speed and size. Regarding DDR4 modules, CAS timing of 14 or 15 is recommended but as it may result in higher cost, a CAS of 16 is what most users will find balanced for price and performance.
In the following text, we will discuss these aspects in detail.
What is Good RAM Latency?
You may know that latency is about timing and plays a role in the performance of RAM modules. Therefore, you may like to find out about good or superior latency.
There are two parameters mainly considered when talking about RAM latency: CAS latency and true latency. Concerning both, a low value indicates a good latency. When it comes to a memory upgrade, low latency RAM should be considered among RAM options having identical clock speed and size.
Concerning DDR4 modules, a CAS latency of 14 or 15 is recommended but may come at an extra cost. You can opt for RAM with a CAS of 16 that’s balanced in terms of performance and price and is suitable for most users with Intel and AMD based systems. It would be fitting for multiple purposes whether productivity or gaming.
Regarding RAM modules with identical size and different clock speeds and latencies, preference should be given to the one with a higher clock speed.
A Brief Overview of CAS Latency
CAS (Column Access Strobe) latency is a measure of the clock cycles passing when the RAM module accesses a particular dataset in its column and making that data available after being instructed by a memory controller.
CAS latency can be specified in different ways. A RAM module or kit with a CAS latency of 18 can be written as CAS18, CL18, C18, or with CAS 18 timings.
This information is usually printed on the label of RAM sticks or mentioned as part of the specifications. It’s the first number that’s specified after CL; an example is CL14-14-14-34 that denotes a CAS latency of 14.
Why Lower CAS Latency is Better or Highly Rated?
We discuss here an important aspect that would help you in buying RAM for better performance.
Imagine you are given two RAM kits to choose one. Assume both are of the same size i.e. 16GB and the same clock speed (i.e. 3200MHz). One has a CAS latency of 17 while the other one has a CAS latency of 18.
So, on what criteria would you choose the one?
RAM modules with a CAS latency of 17 will have 17 clock cycles when a request is sent by the CPU and when the data is output by the RAM. Contrary to this the RAM with a CAS latency of 18 will have 18 clock cycles when the CPU sends a request and the data is made available.
Thus, it can be deduced that the RAM with a CAS of 17 will be quicker than a RAM of CAS 18 because the delay between operations is 1 cycle less. We can infer that the kit with the lower CAS latency will be better than the kit with the higher CAS latency provided both have the same clock speed and size.
RAMs with a lower CAS may be pricier than the higher CAS. Thus, we recommend choosing a memory that suits well within your budget and gives the desired performance.
Why CAS Latency Matters for DDR RAM Generation?
You may know about the different generations of DDR RAM and the most used today i.e. DDR3 and DDR4. The latter is newer and better in terms of clock speeds and power efficiency.
DDR3 RAM has a CAS latency of generally 9 or 10, while DDR4 RAM has more CAS latency that usually starts at 15 and goes all the way to 19. However, it’s not uncommon to find DDR4 modules with a CAS of 14. These can be said as better than the ones having CAS of 15 to 19 provided the same clock speed.
On the other hand, if you compare between DDR3 and DDR4 modules, the latter has more CAS latency. Because the newer generation RAM has more clock speeds, it provides better performance as compared to DDR3.
You should also check out the maximum capacity and speed your motherboard and CPU can support along with CAS latency. This would help you to buy compatible RAM that performs better when installed.
A Look at True Latency
There’s another parameter called true latency that would help you to compare the performance levels of different memory sticks.
You can use the CAS latency and the clock speed of a RAM module in the following formula to calculate true latency in nanoseconds:
(CAS Latency/Clock Speed) *2000=True Latency (ns)
The general observation is that the lower the true latency the better it will be, and the superior will be the RAM performance. However, higher CAS latencies and higher clock speeds can result in higher true latency.
Also, there can be situations where you observe a tie in the true latency of two RAM modules. For instance, imagine a RAM kit coming with specifications of 1333MHz and CAS latency of 9 while another kit having a clock speed of 2666MHz and CAS latency of 18.
Though both RAM modules have a true latency of 13.5 ns because the latter has a higher clock speed it will perform better. So, you should give preference to RAM modules with better speeds in general.
Here we described not only what is latency when it comes to RAM but also explained different situations where it can be significant.
When replacing or upgrading memory, you should not only pay attention to what is good RAM latency but other factors also such as speed, size, and motherboard compatibility.
This shows that analyzing RAM only based on latency is not true either.