Crucial Classic DDR5-6400 32GB CUDIMM Dual-Channel Memory Kit Review

TweakTown Rating: 90%

Our Verdict

The quality of this Micron-based kit of CUDIMM from Crucial is obvious once you give it a spin. Not only does it deliver stability, compatibility, and longevity, there is a ton of room in the tank to tinker with the new tech.

Pros

• CUDIMM advantages
• Performance
• Overclockability
• Low voltage

Cons

• Availability
• Oddities in overclocking
• Current cost

Should you buy it?

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Introduction, Specifications, and Pricing

If you made it this far, past the clicks from either social media links or from our home page, we assume you know what RAM is, and that its evolution is part of the game. Not that long ago, we were knees deep in DDR4 samples and have recently had a plethora of DDR5 kits to bring forth to you all, but as more time passed, we have now moved into the newer generation of DDR5 with CUDIMM kits.

For those who have not paid attention in class, CUDIMM is DDR5 with a CKD chip involved in the mix. What is CKD? It is an onboard clock driver, taking the workload off the motherboard and CPU and now putting many of the eggs in one basket. Multiple advantages come from this move, as it eliminates trace length issues, reduces the effect of RF interference, increases the stability of the RAM, and, in many cases, will make it easier to tinker with for all the overclockers out there looking for the next advantage.

Getting into the meat and potatoes of what has us here today is an up-close look at the Crucial Classic Series and their new JEDEC kit to hit the market. Just as when we jumped into DDR5, we used the Crucial DDR5-4800 kit, with the bar being raised by JEDEC, we are now dealing with 6400 MT/s as the baseline for newer systems. As always, this is a binary kit, sticking to all the standards and expectations we've seen from Crucial in the past. The only change is that now, with CUDIMM and their CKD chip, we hope there is a bit more to do than run tests at the new JEDEC speed and show off the new tech.

By spec and JEDEC standards for the new iteration of DDR5. Crucial forwarded a set of CT16G64C52U5, which strangely does not exist outside their site, anywhere in the wild that we could find. However, don't roll your eyes just yet. As our first set of CUDIMM and a go with CKD and its effects, we have wide open eyes at to what this "slower" set of sticks may be able to show us.

On a technical level, passed the MT/s rating, we have a set of naked black sticks, all chips exposed, each housing 16GB worth of density. With the new JEDEC spec comes even more open timings. We used to moan when we saw the OG DDR5 JEDEC recommendations, and at first, and seeing the 52-51-51-102 2T timings doesn't make us all warm and fuzzy, but this is all about widespread compatibility and usability. The last point to make is that with the new JEDEC spec, we are based at 1.10V for all kits, prior to any XMP tweaks manufacturers may make.

Physically measuring the DIMM, we got 133.3mm of length, a mere 31.2mm of height, and 2.7mm thick. Each stick weighs only 15.6 grams consisting of PCB, ICS, chips, solder, and a sticker. As always, Crucial backs their memory with a limited lifetime warranty.

Locating these kits is easier if you do not know the part number, as that gives you limited information. If you just drop into Newegg and search CUDIMM or Amazon, not so much. We noticed immediately that Crucial is charging a huge premium to get your hands on their CUDIMM. Where a UDIMM 6400 MT/s set of Crucial sticks will cost less than $100, the kit we have sells for $233.99. We assume that as this tech goes more mainstream, pricing will lower, but as always, if you want to be first to the egg, you have to pay the price.

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Packaging and Crucial Classic CUDIMM

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As we expected, the Crucial Classic comes in clear clamshell packaging with a sticker offered to deliver the information. On it we see this is DDR5-6400, but CUDIMM (Clock Driver) that uses 1.1V uses CL52, made for desktop use, and even says it's a new form factor. Lastly, above the icons and barcode, we see that this is a 32GB kit comprised of the two sticks you see.

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Flipping over the packaging allows customers to see exactly what they are buying. Not only can you see the sticker that Crucial puts on their sticks, but you can also see the IC, PMIC maker, and CKD chip maker, although you may need to take a picture and zoom in at the store.

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If not for the added circuitry in the center of the sticks, there isn't much to differentiate CUDIMM from UDIMM. In their Classis Series, all the sticks use black PCBs and have eight ICs. Being naked keeps the package compact, and a kit such as this will cause no issues with whatever build you compile.

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Outside of the three gold pins at either end, the back of the Crucial Classic shows nothing more than all the solder points. While not classically stylish, we like the effect, but this is hidden most of the time.

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We hope you liked the view we just saw, because the way in which Crucial designs their CUDIMM, everything faces the CPU. What we man to say, is that when installed, this is the view you will be given.

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While we are not looking at fancy spreaders, this image shows us two things. The PCB edge is cleanly cut, and thick, but overall, these sticks are super thin, where the PMIC layout is the highest point.

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It shouldn't take a genius to know that when buying Crucial memory, you are buying Micron ICs, as shown by the logo on these four. The ICs in question are the 4JD75D8DKT chips. While set at 6400 Mt/s by the JEDEC profile, they do house a bit extra in the tank.

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Thew PMIC central to this image is made by MPS and is the PMIC5100 series and is unlocked for voltage adjustments. The SPD chip at the top and the CKD chip at the bottom are made by Montage.

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Freshly installed into our new test bed, the Crucial Classic fits right into the blend of matte black, grays, and pops of color here and there.

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Just to brighten up the place, we went ahead and powered the system to show the Crucial in a different light. In the right situations, we did get color on the edge of the PCB with the Q60 backlighting, which is cool, since there is no lighting in the kit.

Mem TweakIt allows us a one stop shop for everything timings related. Tab one4 shows all of the basics many are used to seeing, and to be honest, there is noting unusual seen in any of the tabs, outside of the timings being open for stability and compatibility.

Test System Details

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To obtain the Intel CPU-Z screenshots, you will see directly following this image; this is the system we used to do it, as well as to get the results seen in the following pages. Thanks to ASRock, our wallet, HYTE, Patriot, GIGABYTE, and be quiet! for supporting us with this venture. Detailed specifications of the system can be found below.

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Our Crucial Classis are easy to set up. Clear CMOS, insert the sticks, power on the system, venture into the UEFI, and set the defaults, save, and exit. On the SPD chips is a single profile set to the new JEDEC standard, which boots this kit only one way, the way it's shown here. 6400 MT/s with 52-51-51-102 2T timings, just like the packaging and specifications said.

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We threw some effort into timing reductions, but no matter what we tried, if we changed the CAS timing, the kit would not boot properly. However, we were able to take the tCRD and tRP down to 42 without changing anyth9ing else. In fact, once we tried to add voltage to drop them lower, booting became unstable.

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Even with unlocked voltage to supply this set of memory with whatever we wanted, we got the most from this kit at just 1.10VDIMM. While the timings may seem a bit out there, we took this 6400 kit right up to 7866MT/s just by pushing the memory speed option until we ran into instability. Impressive! Sadly, any adjustments to timings made the entire mission fail immediately. Only when the ASRock OCF was in control of timings could we make gains.

Chad's Intel DDR5 Dual-Channel Test System Specifications

Intel Performance

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Compared to the previous JEDEC specifications, the Crucial Classic at 6400 MT/s does well to land at 95,824 MB/s out of the box. A timing reduction hurts AIDA Read throughput, but pushing speed gave us another 23.317 MB/s throughput, closing that gap to the 8200MT/s example.

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AIDA Write performance starts a bit lower, this time at 85,342 MB/s, which is well above the old spec. We gained just 597 MB/s tightening timings, which is essentially a wash, but again, added speed netted us a boost of 11,422 MB/s over JEDEC.

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The Copy results are like the Write results, where we start off at nearly 85,000 MB/s. However, tightened timings delivered 2164 MB/s over the JEDEC result. Smashing our ideas of what sort of performance boost we might see from more speed, we got an astounding 16,513 MB/s more from this kit with the slightest of efforts.

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Latency across the board is worse than we saw with our previous intel system, but if they are all higher, it is still a level playing field worth looking at. The previous JEDEC standard is incredibly slow, setting the high end of the spectrum at over 100ns. While the new Crucial Classic does moderately better, we can see how far we can drop latency lower by what the 8200 MT/s kit provided.

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Super Pi shows that we can complete the 32m run in five seconds less time than the previous JEDEC spec with the new one. Changing the secondaries added 16 seconds to the time to complete, and even with added speed, the test ended at the same time as it does with the new JEDEC setup, right out of the box.

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PCMark 10 runs through a multitude of tests and delivers more of an efficiency rating to the kits tested. As we can see it is much better than the 4800 MT/s results and climbs right up there behind the 8200 MT/s kit, with just a little bit of tuning.

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File compression in 7-Zip gets a nice boost from the upgraded JEDEC standard that Crucial has in this kit. Nearly twenty-three seconds faster than the 4800 MT/s kit is a great start. We removed another eight seconds with tighter timings, and with more speed, we are now thirty-two seconds faster. Great for this kit, but we do see there is a fair bit of room between Crucial and their Viper Extrteme.

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We also see great things in transcoding with Handbrake. We see thirty-one seconds as the performance boost versus the old JEDEC spec, which is great. You can reduce that time by another seven seconds, tinkering with timings, and if that isn't enough, you can increase speed and get another eight seconds of life back.

Final Thoughts

Our first look at CUDIMM DDR5 is a pleasing yet odd ride into new technology. While out-of-the-box performance is better than the old standard, as one would expect, there are new things to learn along the way. With CUDIMM kits, you cannot overvolt the traditional way - we had to use PMIC voltage controls this time. Timings seem to matter even less than in previous iterations, but it does seem to have a huge impact on latency. Specifically, we found that adding voltage pretty much killed any attempts to overclock, and the fact that the CAS timing won't budge is not unusual; we have seen that in the past; we just had hoped to get the CAS somewhere near the ability of the secondaries. While expensive, they have shown some value over previous JEDEC spec kits.

On the other side of things, while performance was sometimes better than expected in the array of tests, the flexibility of this kit is a bit insane. Being able to take the timings down that far on a kit designed to run the minimum is music to our ears. Adding speed has never been easier in any kit of DDR5 we have tested. At some point, you typically need to adjust voltages, but with the Crucial Classic, we took them right up to 7866 MT/s just by changing the speed setting in the UEFI. The motherboard takes over for us and sets the timings, but our voltages never changed. We got all the way there with just 1.10 VDIMM and nothing extravagant in the supporting voltages. As we saw, even at CAS62, this kit was willing and able to put up some impressive results if you are willing to take the time to tinker and test.

As we mentioned earlier, being on the bleeding edge of PC technology is never cheap; just look at the cost of the 5090. However, you won't be dealing in thousands of dollars, but you will have to consider spending hundreds of dollars on what can only be described as a baseline JEDEC standard offering. At $233.99, we did end up with a set of DDR5-7866, but that is not going to happen for everyone. While this is a terrific set of RAM with all things considered, we still must consider the lack of spreaders, ARGB lighting, or the ease of XMP, but the Crucial Classic is designed to work in any situation with any supported parts. That is not something that can be said for all the DDR5 we test.

For those looking for stability, performance, and compatibility with a CUDIMM-supported motherboard, this is not a bad place to start. For the average user, this kit will do anything you need, and not cause any headaches, other than deciding on if you want to shell out this amount of money or wait until things settle down a bit more.