The RAM spec everyone obsesses over matters less than this one most people ignore

Buying RAM feels like a walking nightmare at times. You're not only competing with the super-high prices that are seemingly refusing to come back down, but also with some of the marketing language used to sell you hardware you might not need.

When it comes to RAM, the headline spec that everyone leads with isn't always the one you should be looking at. RAM frequency is fun because it looks big and can tell you about performance at a glance, but it's far from the only spec you need to check when buying RAM.

The actual spec you need to look for gets far less attention, yet has a bigger impact on how responsive your system actually feels: latency.

Frequency dominates the conversations

What frequency actually tells you

It’s easy to see why frequency dominates the conversation. It’s simple, clean, and easy to compare within the RAM generation. Number goes up, RAM gets faster; it's that easy.

Basically, frequency explains how much data your RAM can move in a given amount of time, and is typically given as two measurements:

• MHz: Measures the clock frequency of the memory, i.e., how many cycles the memory can complete in one second.
• MT/s: Stands for megatransfers per second, and measures the effective memory data rate, i.e., how many times data is moved in one second.

Both are essentially measuring how much data can move between your memory and CPU per second, and in both cases, higher is better, and certain tasks benefit more from higher frequencies, too, like video editing, 3D rendering, certain types of games with heavy asset usage, like Cities: Skylines 2, Microsoft Flight Simulator, and so on.

But frequency isn't the whole picture when it comes to memory, and it certainly isn't the be-all and end-all for most folks. It's good to know how much data your memory can shift in a certain period, but you also want to know how quickly it responds when your system actually asks it for something.

That’s where latency comes in. Specifically, CAS latency (often written as CL) and the wider set of memory timings determine how many clock cycles it takes for RAM to begin delivering data after a request is made, basically measuring the delay. When it comes to latency, lower is better, meaning a faster response to any requests.

So, where frequency measures "how much," latency measures "how quickly it starts."

First-word latency ties it all together

Faster kit isn't always faster in practice

Now, there is another term that actually ties frequency and CAS latency together, which is known as first word latency. It's a more realistic indicator of how RAM may perform in real-world situations, detailing how long it takes for the first bit of data sent to arrive.

In that, it works as the middle-ground between the headline-grabbing frequency speeds and less eye-catching latency responsiveness timings.

When you look at a set of RAM modules for sale, the RAM latency is listed as a timing string that'll look like 32-40-40-103. It's the first number that represents the CAS latency.

Now, here's the bit where it gets a bit murkier. CL ratings really need the frequency to make absolute sense. Seeing a CL rating of "32" on its own doesn't explain enough about the timings to explain memory performance. A CL30 rating on a DDR5-6000 kit and a CL36 rating on a DDR5-7200 kit look different on paper, and it's difficult to compare them directly because those cycles are running at different speeds.

You're looking for the golden zone of frequency and latency

Higher and lower, but with constraints

So, higher frequencies are great, right? And lower latency is also great, so we know exactly what to aim for: memory with super high frequency values and the lowest latency rating we can find.

Womp womp. You think it would be that easy?

That is the general idea, to have high MHz and low CL, but the two ratings actually run in tension together. That's because the higher the memory frequency, the more difficult (and expensive) it becomes to deliver lower latency with tight timings.

Past a certain point, you're relying on overclocking timings and fiddling with voltages, which, for most folks, is probably beyond where they want to be when it comes to dealing with RAM. It's why buying 8000MHz RAM isn't quite the upgrade you think it'll be.

Right, but why isn't DDR5-4800 CL15 and DDR4-4800 CL15 the same?

That's another slight issue you have when trying to work out RAM performance, especially when it comes to cross-generation performance. Typically, anything from the previous generation will perform more slowly.

DDR5 > DDR4 > DDR3 is a general rule of thumb because of how memory works at a fundamental level. DDR stands for Double Data Rate, and it's named as such because DDR memory transfers twice per clock cycle — that's where the "double" comes from. So a DDR4-4800 kit has an actual internal clock of 2400MHz, and a DDR5-4800 kit also has an internal clock of 2400MHz. So far, so identical.

But the difference is another memory feature you won't see advertised (because it's not really needed to be), something called burst length. RAM burst length basically refers to the number of data locations memory can read or write to at once, and this typically doubles with each generation.

So, DDR4 had a standard burst length of 8, while DDR5 increases to 16.

It all means that while the numbers on the packaging between the DDR4 and DDR5 look similar, the bandwidth of the newer generation is effectively doubled.

So, how do you buy RAM that's actually faster?

In a world where RAM prices increased faster than I can drink a cup of tea, getting value for your hardware has never been more important. There is another way to make sure you're getting marginally faster RAM, and that's to convert the numbers into real-world outputs using the following formula:

(CL ÷ transfer rate in MT/s) × 2000 = latency in nanoseconds

The number you get in nanoseconds is actually the faster memory kit — but stick to measuring one generation of RAM rather than trying to compare across standards, otherwise it stops making sense (due to the aforementioned burst length!).

In this, you may find that in terms of price to performance, certain memory kits perform better than others.

Just remember that RAM marketing is designed to sell you on the number that's easiest to put on a box, and that's always been frequency. But once you know about latency, you can start to find the really good memory deals.