We know, we know. Advances in memory technology aren’t usually as sexy as, say, a game-changing display format. But these steps ahead are integral to the computer industry, fueling the performance gains we’ve come to expect from PCs. And the memory industry is constantly under the gun to advance and introduce new technologies that push capacity and bandwidth to new heights.
Why all the windup? We may be on the verge of a big step forward in memory tech. Recently, the industry unveiled CUDIMM modules, which use a relatively simple method to boost memory performance. (The industry’s memory-standards keeper, JEDEC, has put the seal on them.) Nothing is guaranteed, of course, and other technologies are developing at the same time. But if CUDIMMs pan out and gain popularity, they could represent the next widely used memory standard in the PC world.
What Are CUDIMMs?
The term “CUDIMM” stands for “Clocked Unbuffered DIMM,” with the “DIMM” standing for “Dual Inline Memory Module.” (We’d better stick with the acronyms.) CUDIMMs feature just one major change from standard DDR5 DIMMs: a dedicated chip that generates a clock signal. In contrast, a more traditional memory configuration uses a clock driver on the motherboard or host processor. Let’s break that down.
Clock drivers or generators of various kinds are a big silicon deal. Basically, they determine the operating clock speed of all computer chips. They also help keep the various chips in your PC synchronized so that they can communicate correctly with each other. As we said, these clock drivers are typically found on the motherboard or host processor.
(Credit: Joseph Maldonado)
In most cases, your system’s RAM derives its clock speed from this base clock. And that’s where complications can arise.
The higher the clock is, the harder it is to maintain the signal integrity over distances. Yes, even at the microscopically tiny distances involved inside a computer, an electrical signal deteriorates the farther it travels. This problem isn’t unique to memory; it’s a universal truth about electrical signals. For instance, this is why 5GHz Wi-Fi signals don’t transmit as far as 2.4GHz signals. (The issues aren’t exactly the same, but you get the idea.)
The problem keeps getting thornier because we keep pushing for faster and faster machines. RAM has advanced to such high speeds that the signal doesn’t always reliably make it to each memory chip on a memory module without sliding off spec. And if all of these chips don’t perform identically to each other, you end up with instability. As a result, you have to put a cap on the possible top speed.
(Credit: Joseph Maldonado)
Needless to say, hardware manufacturers have attacked the signal-degradation issue in many ways, such as new signal encoding schemes and adjustments to the memory controllers and RAM modules themselves. These efforts have been effective over the years, but, as we said in the intro, the drive for more memory speed never lets up. Now we’ve got CUDIMMs, one of the more noticeable and tangible changes to memory in recent years.
What do they do? Instead of relying on a central clock driver, each memory module gets its own driver. That means the clock generator is far closer to the memory chips on the DIMM than a clock generator on the CPU or motherboard could ever possibly be. The signal doesn’t have to travel as far, and there’s less chance the signal will differ from chip to chip. Presto: stable operation at even higher clock speeds.
How Do CUDIMMs Differ From Ordinary DDR5 DIMMs?
That, in a nutshell, is the only real difference between CUDIMMs and DDR5 memory: the inclusion of that clock generator. Thanks to this new addition, you’ll see CUDIMMs rated to operate at higher clock speeds than ordinary DDR5 DIMMs, with CUDIMM kits now commonly rated from 8,000MHz to 9,000MHz. They may use higher-end DDR5 memory chips to further push clock speed, but they do, in fact, still use DDR5 memory chips. You’ll even see “DDR5” on the side of most, if not all, CUDIMM kits, like the Kingston memory kit shown here.
(Credit: Joseph Maldonado)
We could see CUDIMM technology used on future types of memory, too. It’s only a matter of time before DDR5 will be replaced with something new, and that next-gen memory might also use CUDIMM technology (unless some better memory technology comes along to replace it).
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What Kind of Systems Use CUDIMMs?
The current crop of CUDIMMs on the market uses the exact same package and edge connector as standard DDR5 DIMMs. They should function normally on any motherboard that accepts DDR5 DIMMs—but not necessarily at their peak rated speed. To take full advantage of the CUDIMMs, the motherboard needs to recognize them and support them, allowing the clock driver on the CUDIMMs to do its thing.
If you plug CUDIMMs into a standard motherboard that only supports “ordinary” DDR5, the CUDIMMs won’t use their built-in clock drivers. Instead, they’ll work just like standard DDR5 RAM modules, so you very likely won’t hit their rated top clock speeds. Sure, you’ll get the speeds common on standard DDR5 DIMMs, say in the 5,000MHz, or possibly 6,000MHz, range. Just don’t expect to get the memory running at 8,000MHz or higher, as many CUDIMM kits are rated for.
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(Credit: Joseph Maldonado)
Long story short, there’s little reason to buy CUDIMM RAM currently for AMD PCs, or for older Intel systems like any LGA 1700 PCs with 13th Gen “Raptor Lake” or 14th Gen “Raptor Lake Refresh” processors. Only Intel’s latest platform, LGA 1851, which supports the company’s newest desktop chips, the Core Ultra 200S (code-named “Arrow Lake”), currently supports CUDIMMs. But that is likely to change in the near future.
Also expect to see a related standard pop up for laptops and other compact devices called “CSODIMMs,” for “Clocked Small Outline DIMMs.” In essence, these will be shrunken versions of desktop CUDIMMs. But for now, you’ll want to leave incorporating CSODIMMs to laptop makers. They’re not something to upgrade “to” in an older laptop.
Do You Need CUDIMMs Right Now?
Support for CUDIMMs and CSODIMMs is likely to spread to other platforms soon, and memory makers big and small are now offering CUDIMM kits, among them ADATA, Corsair, Crucial/Micron, G.Skill, and Kingston. Expect to see kits ranging from 32GB to 128GB.
But we have some key buying advice: Don’t rush to buy CUDIMMs or CSODIMMs now with the intention of upgrading the rest of your PC later and moving the modules to a motherboard that supports them, unless that move is imminent—say, within a year.
Why? CUDIMMs cost more than standard DDR5 RAM of the same capacity and general speed class. RAM tends to get faster, better, and cheaper over time, so if you’ll be waiting years to put those modules into a system that supports CUDIMMs, the modules will likely be a better value if you buy them then, as opposed to now. Unless you are building an Intel “Arrow Lake” system this year, you can likely take a pass on buying CUDIMMs right away. But keep a sharp eye out for them, and plan accordingly if you’re looking to build a PC anytime soon.
About Our Expert
Michael Justin Allen Sexton
Senior Writer, Hardware
Experience
I have been interested in science and technology for as long as I can remember, spurred on by a fondness for video games. I learned to work in Windows and manipulate files to get buggy games to work, and I learned to build and upgrade PCs for better performance.
In my role at PCMag for the past four years, I’ve deeply enjoyed the opportunity to share my knowledge and expertise. Before PCMag, I wrote for Tom’s Hardware for three years, where I covered tech news, deals, and wrote some hands-on reviews. After working as a PCMag contributor for a time reviewing desktops, PC cases, budget processors, and motherboards, I now focus on testing and reviewing processors and graphics cards and sharing my insights on the industry.
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