The arrival of the new Ryzen 7000 CPU family means that PCIe Gen 5 is now a reality on both AMD and Intel platforms. But let's face it. Your current PC most likely does not have a PCIe 5.0 M.2 slot. That's where the WD Black SN850X, the last bastion of Gen 4 SSDs, comes in. [The WD_Black SN850X is reviewed in a 1TB configuration, but it is not exactly a brand new drive, but an improved version of the existing WD_Black SN850 non-X (opens in new tab). This is not a bad thing. After all, the older SN850 was one of our favorite M.2 SSDs (opens in new tab). It is fast, competitively priced, and backed by one of the best brands in the storage industry. However, the old SN850 ran a little hot.

The new WD Black SN850X has a couple of solutions. First, our review configuration is clad head-to-toe in WD's signature armor-plated style cooling system. While the older SN850s offered this cooling solution as an option, the newer drives have a modified thermal profile. This is specific to the SN850X.

Of course, if your motherboard comes with its own M.2 SSD cooling kit, you may not want to pay extra for a self-cooling SSD; WD can accommodate that as well. The new X model, like its predecessor, is available both with and without a heatsink, with the latter option being about $30/£25 cheaper.

In fact, in many ways, this new X model is a meld of the existing SN850. It's now in the ubiquitous M.2 2280 form factor and offers four lanes of PCIe Gen 4 connectivity. However, the 1TB model we reviewed is now an entry-level option; the 512GB model is no longer available; and the 1TB model is now a 4-lane, 4-GB model. Additionally, WD's in-house controller chip has been revised, although detailed specifications have not been disclosed.

The drive's TLC flash memory chips have likewise been upgraded from 96-layer TLC chips to the new 112-layer technology, which is still a bit behind the new 176-layer NAND from the likes of Micron and SK Hynix. Nevertheless, the new SN850X claims higher performance than before. The question is whether the SN850X has the performance to compete with 4th generation speed freaks like the SK Hynix Platinum P41.

For this 1TB model, WD describes an increase in write speed from 7,000MB/sec to 7,300MB/sec and an increase in read speed from 5,300MB/sec to 6,300MB/sec. This is about the same level as the SK Hynix drive. turning to IOPS, the older 1TB SN850 recorded 1M read and 720K write. WD says the revised X models will support 1.1M and 800K read and write, respectively. the SK Hynix's IOPS are 1.4M read and 1.3M write. 1.4 million and 1.3 million writes, not bad.

As for write endurance, this 1TB drive is rated at 600TB, the same as older non-X drives and other big brand 1TB drives like the Samsung 980 Pro. In reality, it will write hundreds of gigabytes daily for over five years.

Unique to this WD drive is the latest 2.0 version of the company's drive management software Game Mode, which WD claims improves game load times and caches game data predictably through a so-called "read look-ahead" algorithm. The company claims that the so-called "read look-ahead" algorithm improves game load times and caches game data predictably. Now, the system detects that a game has been loaded and automatically executes it. It is difficult to say how much difference such a feature would make in the real world. But it is unlikely to be revolutionary.

What we can say with certainty is that the peak sequential throughput is in line with WD's numbers: CrystalDiskMark results clear 7,300 MB/sec read and 6,300 MB/sec write, making it a very fast 1TB drive. This makes it an extremely fast 1TB drive. Only the 2TB models, including the aforementioned SK Hynix P41, are faster.

Lower operating temperatures are another clear advantage of this new drive. The older SN850 recorded 77°C. The new drive is only 58°C under sustained load. This is a very worthwhile improvement. While the SN850 was already a superior drive, there is not much obvious improvement in other respects: the 4K random access results are a bit disappointing, with little improvement. Similarly, no significant improvement can be expected in overall system performance measurements such as PC Mark 10.

Finally, the SLC cache allocation on the new SN850X is unchanged. As a result, an empty drive can write approximately 300 GB worth of data at peak performance before the fundamental performance of the TLC NAND chip is exposed. This should be sufficient for most, if not all, users.

All of this does not necessarily mean that the new WD Black SN850X is a revolutionary leap forward. In fact, in actual use, it would be hard to notice any difference between it and the existing SN850 drive. But that's because the SN850 is a very good SSD. The exception is the operating temperature. Fortunately, this new X model clearly operates at lower temperatures.

For most PC applications, this probably won't be an issue. However, for small form factor rigs and perhaps gaming laptops, it can help a bit. In that regard, most applications would choose the less expensive bare drive over this more expensive model with a heatspreader. The modified SN850X is, after all, essentially a low-temperature operation.