Lexar is really making great progress in the SSD market, their NM790 is a smash hit and selling very well. While the company's previous versions of the NM790 lacked a dedicated heatsink, the NM790 in this review comes with a full-size metal cooling solution. While that might be overkill for the majority of users, people still demanded such a variant. Especially gamers who want to expand the storage on their Sony PS5 will benefit from this model, because Sony requires a dedicated heatsink according to their specs list. Internally, nothing has changed, the NM790 with heatsink is powered by the same Maxiotech MAP1602 controller that we saw on other models. There's no change to the NAND flash either, the NM790 is built using YMTC 232-layer 3D TLC flash. A DRAM cache is not included, ensuring the low price point can be achieved.

Synthetic performance results of the Lexar NM790 are uninspiring. While sequential throughput does achieve the promised 5 GB/s, random writes are considerably lower than the competition. With just 26200 IOPS at 4K random write, the NM790 runs this test in SATA territory. It seems that the drive's DRAM-less nature is responsible for these results. Our synthetic tests are performed with a relatively large 32 GB work area, whereas CrystalDiskMark uses a tiny 1 GB size, to show best-case results. Other drives using the same controller, but with 1 TB and 2 TB capacity, use a 32 MB Host-Memory-Buffer area. On the NM790 the HMB is sized at 40 MB, which is relatively smaller. Considering the 4 TB capacity, I would have expected 64 MB, or more. Apparently the maximum HMB size on the MAP1602 is 40 MB, which makes it difficult for the controller to optimize random writes over a larger area. On drives with physical DRAM cache, the DRAM stores the mapping tables of the SSD (to figure out where a given piece of data is located). On DRAM-less drives that's handled by some controller magic, optionally with the help of the Host-Memory-Buffer area.

Still, despite some weak synthetic results, the real-life performance of the NM790 is outstanding. It is able to beat every single PCIe 4.0 drive out there, with the exception of the Samsung 990 Pro, which it is able to match—very impressive! That's why real-life testing is so important. We test actual applications, not replays of disk traces, and the drive is filled to 80% of its capacity, not an empty drive like most reviewers do. This approach puts additional strain on the various algorithms and the SLC cache, just like in real-life. We've seen this in several recent reviews: times have changed and you can no longer dismiss all DRAM-less drives—the controller and how well it handles this configuration matters, too.

Thanks to its pseudo-SLC cache, the NM790 can easily absorb large incoming write bursts. A SLC capacity of 270 GB is "good," maybe a bit small in absolute terms when considering that this is a 4 TB drive. Providing 270 GB in SLC mode, which uses three times the capacity, means that up to 810 GB, or 20% of 4 TB gets occupied by the SLC cache. Filling the whole drive completed at an average speed of 1.28 GB/s, which is good, but weaker than what the best PCIe 4.0 SSDs offer.

Our new power consumption tests are a great match for the Lexar NM790. It is the most energy-efficient drive in the whole test group—more than twice (!) as efficient as your typical Phison E18+Micron 176-layer drive, a bit less in writes, but still topping our charts. Our laptop idle power results show that the drive is able to enter its lowest power state with PCIe ASPM enabled. This was a problem on the Netac NV7000-T, but works on the Acer Predator GM7. It seems that there's still some firmware optimizations that Maxio can do for this scenario.

This high energy-efficiency helps the NM790 stay cool, especially when the big heatsink is installed. In our thermal stress test we saw no thermal throttling, which is a highly impressive result, because we're using a watercooling solution on the CPU, which means there's no airflow from the CPU fan. I really like what Lexar has been doing with the heatsink design visually, too. It's subtle, with a nicely textured black surface.

The Lexar NM790 is widely available everywhere. The 4 TB heatsink model is currently listed online for $280, which is a $30 increase over the variant without heatsink. This is a fairly steep price increase, considering that M.2 NVMe heatsinks can be found for $10 on Amazon. On the other hand you get full warranty for the heatsink and it comes preinstalled, so you can plop the drive right in and start using it. Experienced users can definitely save some money here by opting for an aftermarket heatsink. While there's some 4 TB QLC drives available for $150-$190, these offer terrible write performance once the pseudo-SLC cache is full—not worth the savings. A strong alternative is the Silicon Power XS70 ($220, Phison E18+ Micron 176-layer). Many popular SSDs like the WD SN770, Solidigm P44 Pro and Atom 50 don't exist as 4 TB version. WD Black SN850X 4 TB costs $290 right now, without heatsink, $350 with heatsink—too expensive, just like the Kingston KC3000 for $350 and the PCIe Gen 5 Crucial T700 for $450. The strongest competition for the Lexar NM790 with heatsink is the NM790 without heatsink and similar MAP1602 drives, some of which come at lower pricing, especially if you're willing to shop on AliExpress.