RAM 101
When it comes to RAM, the internet is full of some great resources but, there’s a problem. All of this data is scattered through many different types of media and unless you know exactly what you’re looking for then you’re probably going to miss it. This resource aims to consolidate as much of this information as possible, so that the most common questions can be answered simply and to help provide some guidance for new and experienced PC builders alike. This list isn’t exhaustive and the information here is fairly basic, but it should be enough to start you on your journey. Some of the most common questions I get are related to this so instead of sending 20 links to different bits of information, it’s all here in black and white. I hope you find this information somewhat useful and that it helps to answer some of your questions.
For Reference: DDR is “Double Data Rate” and RAM is “Random Access Memory”.
Introduction
Rated Kits
(RAM Speed and Capacity)
When purchasing a kit of RAM, it's important to know that the ratings for this RAM are only related to the actual kit. For example, If you've bought a 2x16gb (32gb) rated at a speed of 6000MHz, this only takes into account this kit and nothing else. Should you choose to upgrade capacity to 4x16gb (64gb) then there are further implications. The kit is no longer rated at that speed and this will need to be taken into account regardless if you've bought the exact same SKU of the RAM.
To put it bluntly: 2 separate kits rated at 6000MHz each are not rated for that speed when combined. That speed is rated solely for what you get in the individual package.
Now, this isn't to say that the kits wont work together, there's actually a very good chance they will if they're the same SKU and version type, but there may be a trade off, at this point you'll need to decide whether you want to go for Speed, Capacity or somewhere in between. The best way to look at this is to imagine a slider: One side you have Capacity and the other is Speed. You can slide the selector where you want but you'll veer more toward that type you're aiming for.
Capacity
Speed
Ultimately, if you want to be running 4 sticks of RAM, you'll want to buy them as a single kit. This will likely be more expensive than 2 individual kits of 2 but that's because this kit is tested and rated at those rated speeds. Want to run 8 sticks? I personally wouldn't risk buying 4 kits of 2 as this will run the risk of many stability issues.
Now, what I want you to do is to consider the reasoning why most professional overclocking boards only come with 2 DIMM lanes for RAM.
Spoiler alert: It's for Speed!
Capacity vs Speed
(Workload vs Gaming)
When choosing an upgrade for your system, you need to take into consideration what your desired result is. You may think when building or buying a system that you'll get just 2 sticks to begin with and upgrade to 4 sticks later but the real question is, do you need to?
Scenario; it's 2023, you're big into your gaming and have 32gb of RAM. You don't do any rendering or editing so is 32gb enough? Truth be told, it's overkill. There is absolutely no reason to upgrade outside of that as you'll just be putting money into your system with diminishing returns, there's a possibility that by upgrading your RAM that you may need to make the trade off and lower your speed. Why not save yourself a penny or put that money towards something that will actually give you more performance?
So in what case would you choose higher capacity over speed? This will be workload related tasks such as rendering, video or image editing or perhaps even automation. In this scenario, whilst speed would also be nice, it's generally better to go for a much higher capacity. Again, this goes back to the trade off.
Consider your workload before choosing your RAM:
Gaming = Speed
Workloads = Capacity
Is your RAM showing with only half the speed? Don’t forget you need to multiply it by 2 because it’s “Double Data Rate” (DDR#)
Kit Sizes and Dual Channel
(Kits of 2, 4 and 8+)
To reiterate some points here, it's always better to buy a kit with the intended amount of RAM sticks. Why are kits sold in increments of 2? That's simple really and it pretty much starts and ends with dual channel. I mean, how often do you see single sticks of RAM on sale?
First, lets start with dual channel. RAM is currently being designed to run in dual channel as it simply performs better than single channel, the memory has 2 lanes to operate at once without needing to wait for the previous request to complete. That's pretty much it, but now you're possibly asking if 4 sticks means quad channel. Well, not entirely... Though you may have a quad-channel kit of RAM, you also need to take into consideration whether the CPU and the motherboard can support this. The same thing goes for octo-channel.
So what would be best for performance? 2 sticks of 16gb (32gb) or 4 sticks of 8gb (Still 32gb). Truth be told, there's no 'one size fits all' result. They're both better at doing different things and the thing that will show the most difference between the 2 options would be the cost difference, not to mention the extra points of failure. Like I've mentioned already, Overclocking boards tend to stick to 2 ports for a reason. The main point between these configurations is that there are no wrong answers, it just needs to be treated on a use case basis.
To close this section, it’s worth mentioning that dual channel isn’t defined by how many sticks you have. For example, a single stick of DDR4 will run in single channel whereas a single stick of DDR5 will run in dual channel.
Integrated Memory Controller (IMC)
(Can your CPU keep up?)
You may, or may not have heard of the "Silicon Lottery" when it comes to your CPU, especially when it comes to the capabilities of the CPU itself. Well, this also applies to the IMC. This is important to know when looking at higher speed RAM kits and is also a cause for confusion and potentially frustration when it comes to achieving higher speeds, and understandably so because this isn't something that is listed as a disclaimer anywhere. So here's what you need to know because this is just as important as the RAM modules themself.
Let's say you've just bought a nice DDR5 kit that is rated at 7800MHz. Without being told or learning the hard way, you'd expect to be able to apply XMP and the system just work at that speed. Well, that's only a third of the story. Other factors to achieving this speed are the motherboard and the CPU. What are the chances of getting 7800MHz running on a B660 board with good stability as opposed to the current reigning champion for the LGA1700 socket, the Z790 Apex? I won't go into too much detail there, point being is that the board also makes a noticeable difference.
Back to the RAM though, when you see a kit of RAM that is rated for 7800MHz, this doesn't mean your IMC is also rated to that speed. A little bit of trivia for you, do you know what the rated spec in terms of memory speed is for the 13900ks is? Well, it's not 7800MHz that's for sure! Whilst it's possible you can run this speed, you'll need to essentially win the silicon lottery or somehow obtain a golden sample. These don't come by easy and you could potentially try thousands of CPUs before you'd ever find one that will ever reach that speed, let alone be stable for long periods of time. Of course, this isn't to say you can't find a CPU that would reach that speed, it's just best to keep expectations within reason. Long story short: Your RAM is rated for that speed, your CPU isn't.
As a disclaimer, changing the speeds, voltages or even timings is classed as overclocking your RAM and this may have some implications in terms of warranty. It's best to know where you stand in the event of a failure if you've been overclocking your RAM. You may also not know this but using profiles such as XMP, DOCP and EXPO is also classed as overclocking. Again, check your warranty terms, including for your CPU where RAM is concerned.
On certain high end boards, you may be able to find some type of rating for your silicon quality/predication for your CPU in the BIOS. In some cases, you may be able to get an overview of the IMC rating. However, this is to be treated purely as a guideline, it's not to say that this is exactly how the IMC will operate and the ratings are largely open to interpretation but this is also something to look out for.
Last note on rated RAM speed, I’ll use a AMD 7800X for an example here. The ‘rated’ speed will change depending on how many sticks of RAM you use. 2 sticks for this particular CPU is 5200MHz whilst 4 sticks is rated to 3600MHz. Be aware of this when deciding how many lanes you want to occupy.
Ok... I guess I've left you in the lurch for the RAM speed rating for the 13900ks... Well, it's 5600MT/s!
Oh look! There's more confusion! Maybe now you're wondering if this is a typo or is there's something you need to know. So to clarify, there is totally a difference between 5600MHz and 5600MT/s, however this doesn't warrant its own section purely based on the fact that the only difference here is the name and it's simply covered by saying this: They're the same thing! Kind of anyway. MT/s is technically the ‘correct’ way to refer to the speed but a lot of manufacturers prefer to use MHz. My pure speculation on this is that "MT/s" probably doesn't translate as well. But yeah, they're the same.
RAM Overclocking
(XMP, DOCP and EXPO)
I'm not going to go into the nitty gritty about RAM overclocking, there is plenty of resource online to help you find that sort of detail, this is just the basics that you may need to know.
These profiles are essentially pre-sets based on ideal testing scenarios. They change voltages, timings, sub timing and more importantly, the speed. Again, it's worth knowing your warranty terms should you choose to use these settings.
There are some fantastic resources out there already about what different timings are, I'll link a couple of Youtube links at the bottom for you to take a look at as this information may not be relevant to you. What I will say though, outside of the timings is the latency.
This can be calculated fairly easy:
(CL / MHz) x 2000 = nano seconds
i.e. A kit of 6000MHz with a CL of 30 would look like the this:
(30 / 6000) x 2000 = 10ns
More information on that could be found on the links I'll provide at the bottom of this page.
Back to the basics of course, you may be wondering what the differences between the 3 profile types are. Well, XMP is a standard that was created by Intel, this means "Extreme Memory Profile" whereas DOCP means "Direct Overclocking Profile", this is essentially AMD's take on the standard set by intel but is tuned to AMD chipsets instead of Intel. Then we have EXPO which is "Extended Profiles for Overclocking". That's it, they're the same thing essentially, they're just loaded with different pre-sets tuned better depending on which platform you're using. Also, for reference, EXPO is best paired with AMD.
As mentioned, these are pre-sets. You could achieve these simply by entering the individual settings without activating the profile. This is really no different to setting an overclocking profile in your BIOS, it's just dedicated to the RAM as opposed to everything else. An option here would be to apply a profile and then further tweak it but I'd highly recommend doing some research prior to this to avoid any potential damage to your components.
Something worth considering for those looking to utilise EXPO memory. EXPO is still in its early phases so at the time of writing so currently, there are no kits of 4 about. Maybe it'll be a thing in the future and I'll correct this later down the line should this be the case but there's a good reason you don't find those kits. Simply put, AMD just can't handle a higher capacity at a higher speed as opposed to Intel. This isn't to be mistaken as a negative take on AMD as they have their pros over Intel for other reasons. RE: the 5800x3D absolutely dominated for a while thanks to the v-cache and the 7000x3D chips should following suite once the issues have been resolved with the exploding CPUs. But yeah, again it's important to manage your expectations on this one and don't expect 4 sticks of EXPO RAM to work at the individual kit speeds.
Adding more sticks of RAM
(And what to look out for)
I'll be honest, chances are that if you've come across this page, it's after the fact you've been looking for some information and you may have already committed the crime of getting another kit after buying the first kit. Specifically, I'd like to give a shout-out to Corsair and their RAM information stickers because this is super useful to know.
If you've come across a kit and taken the time to look at the sticker on the back, it has some important information on there such as the serial number, model and in this scenario, a version number. I'll break it down by the 3 individual sections but please also refer back to the section in regards to mixing different kits.
Version numbers are displayed but can also be a little misleading. It's not to mean that the highest version is the most up to date. You could get 3 kits of exactly the same SKU and one could be V3.25 and the next could be V5.30 with the last being V5.32. This is down to which manufacturer actually made the RAM modules or other components on the stick of RAM, This isn't to say they won't work together, but expect instabilities, especially when applying a RAM profile. I won't get into too much detail on what means what but ultimately, this could be bad but not all manufacturers will display this.
The Model name/number is also important because this is what ultimately defines the spec of the kit, not too much to go into here but this will also help when it comes to identifying kits at a different spec.
Again, but on the subject of the serial number, this is also a really useful indicator of how many issues you'll likely face in getting 2 separate kits working together. If you've bought one kit, you may notice that the serial number are sequential, one after the other. An example could be 1234567890 for one stick and the second stick will be 1234567891. It's essentially just plus one.
If you bought 2 kits at the same time, it is possible you could get 2 kits very close, within the hundreds or maybe thousands of each other but ultimately, the further these get away from each other, the more likely you're going to have some stability issues and see some of the mentioned version number differences.
Identifying a faulty kit
(or testing for stability)
There's loads of tools to help find out issues where RAM is concerned, some are free and some are paid. My favourite 2 for simplicity reasons are Karhu Ram Test and Memtest86 but you're welcome to use anything. This section is probably super useful if you're looking to RMA/Return your RAM due to a suspected fault with the kit.
First thing is to not make the mistake of testing for a fault by using a RAM profile when running these types of programs as all you're proving by doing so is whether your profile is stable or not. To find a faulty kit of RAM, it's super important to run these tests with, and I emphasize, STOCK SETTINGS! Remove the profile and you'll find one of 2 things: A faulty kit of RAM or a faulty IMC on your CPU, with the latter being far more unlikely. I also need to stress that if you're trying to run a kit with a profile enabled that passes fine in stock but not with a profile enabled, you're identifying an instability issue which isn't something that the manufacturers or retailers are responsible for as this is not a fault of the kit. Ultimately, if the RAM passes with stock settings, the RAM and the IMC are deemed as “Fit for purpose”.
There are many troubleshooting steps you could potentially take to help with stability but again, this is something that you'll need to seek out of your own accord because I couldn't list every possible solution here, but a good place to start would be to test different speeds. Try going into BIOS and loading your profile and work down through the speeds in increments of 200-400 MHz until you reach a stable speed.
Another thing you can attempt is tuning the timings but for this, I’d highly recommend researching into this first so you can learn the risks involved. There are many overclocking guides you can find online to learn about this and again, you need to understand your warranty terms. If you’ve tweaked settings and ended up killing a component by doing so, this will void your warranty and leaves you with a potentially expensive paper weight. Don’t go into this blind and hoping for the best.
The most important thing to remember is that though your RAM is rated for a particular speed, it doesn’t mean it will always run at that speed. There are never guarantees made.
Disclaimer: This guide is intended for solely for pre-sales advice. Overclocking your RAM may void your warranty.
Author: Nemo “Nemolition” Shikari
Published: 21st May 2023