Jesper Berg 
In 2022, the WD Black SN850X replaced the SN850 from 2020 as Western Digital’s flagship Gen4 M.2 SSD. Both are still suitable choices for high-end gaming PCs and PS5 consoles in 2023 and both are still widely available.
While the newer SSD lineup offers improvements in certain areas, the difference is by no means large enough to motivate an upgrade from a fully functioning SN850 SSD to an SN850X.
However, if you are choosing between the two for a new build, or to replace an older Gen3 or SATA SSD, it’s good to know how they differ. This is what we intend to explore on this page.
SN850X Vs. SN850: Specifications
First, there are some details worth noting in the official specs.
WD Black SN850 Specifications
| WD Black SN850 Specifications | 500GB | 1TB | 2TB |
|---|---|---|---|
| Form Factor | M.2 2280 | M.2 2280 | M.2 2280 |
| Interface/ Protocol | PCIe 4.0 x4/ NVMe 1.4 | PCIe 4.0 x4/ NVMe 1.4 | PCIe 4.0 x4/ NVMe 1.4 |
| Controller | Proprietary 8-channel | Proprietary 8-channel | Proprietary 8-channel |
| DRAM | LPDDR4 | LPDDR4 | LPDDR4 |
| Memory | 96-layer BiCS4 TLC | 96-layer BiCS4 TLC | 96-layer BiCS4 TLC |
| Sequential Read | 7,000 MB/s | 7,000 MB/s | 7,000 MB/s |
| Sequential Write | 4,100 MB/s | 5,300 MB/s | 5,100 MB/s |
| Random Read | 800K IOPS | 1M IOPS | 1M IOPS |
| Random Write | 570K IOPS | 720K IOPS | 710K IOPS |
| Endurance | 300 TBW | 600 TBW | 1,200 TBW |
| Warranty | 5-Year | 5-Year | 5-Year |
Shopping links: Amazon, Newegg
The original SN850 uses 96-layer BiCS4 NAND memory chips of the TLC (triple-level cell) variety. These have been in production since 2018 and have been superseded by newer types. They offer solid performance nonetheless as well as excellent durability.
All capacities of the SN850 reach 7,000 MB/s in sequential read performance but differ in the sequential write and random IOPS areas. Interestingly, the 1 TB capacity is the fastest of the lot, with slightly better write performance than the 2TB model.
WD Black SN850X Specifications
| WD Black SN850X Specifications | 1TB | 2TB | 4TB |
|---|---|---|---|
| Form Factor | M.2 2280 | M.2 2280 | M.2 2280 |
| Interface/ Protocol | PCIe 4.0 x4/ NVMe 1.4 | PCIe 4.0 x4/ NVMe 1.4 | PCIe 4.0 x4/ NVMe 1.4 |
| Controller | Proprietary 8-channel | Proprietary 8-channel | Proprietary 8-channel |
| DRAM | LPDDR4 | LPDDR4 | LPDDR4 |
| Memory | 112-layer BiCS5 TLC | 112-layer BiCS5 TLC | 112-layer BiCS5 TLC |
| Sequential Read | 7,300 MB/s | 7,300 MB/s | 7,300 MB/s |
| Sequential Write | 6,300 MB/s | 6,600 MB/s | 6,600 MB/s |
| Random Read | 800K IOPS | 1.2M IOPS | 1.2M IOPS |
| Random Write | 1.1M IOPS | 1.1M IOPS | 1.1M IOPS |
| Endurance | 600 TBW | 1,200 TBW | 2,400 TBW |
| Warranty | 5-Year | 5-Year | 5-Year |
Shopping links: Amazon, Newegg
In the WD Black SN850X lineup, the TLC memory chips have been upgraded to 112-layer BiCS5. Performance has also improved somewhat and peaks with the 2TB and 4TB capacities.
SN850X Vs. SN850: Performance
For testing, we have on hand a 1TB WD Black SN850 and a 4TB SN850X. So, while this is not a 100% apples-to-apples comparison, it does represent peak performance from both lineups according to the specifications.
AS SSD
The SN850 manages slightly higher sequential read speeds in AS SSD (which admittedly is not very consistent), whereas the SN850X pulls ahead in the sequential write area.
CrystalDiskMark
Sequential performance in CrystalDiskMark looks similar, but our SN850X takes the lead in terms of read speeds as well, albeit within the margin of error.
Random performance with small files reflects many everyday workloads so it is an important metric. However, the difference is small compared to how it would look for two entirely different models.
Latency/Response Time
We measure response times using Anvil’s Storage Utilities. Again, there is little difference between the SN850X and the SN850.
SN850X Vs. SN850: Gaming Performance
SSD performance in actual games is typically not hugely different between different models. Of course, the SN850X and SN850 share the same (or slightly tweaked version of the same) controller, so these drives should differ even less.
In the standalone Final Fantasy 14: Shadowbringer benchmark, the SN850 was in fact slightly faster than the SN850X (although in fractions of a second and within the margin of error).
The 3DMark storage benchmark measures various gaming-related tasks such as installing, loading, and recording games. These results are more in line with what we would expect, with the SN850X taking the lead.
Conclusion
On average, the SN850X does offer slightly better performance compared to the SN850. However, the difference is typically small and the SN850 even manages to surpass the newer model by a hair in some specific tests. In real-world usage scenarios, like when loading games on a gaming PC or PS5, it is highly unlikely that these differences would be noticeable.
The WD Black SN850X and SN850 are both fast and dependable SSDs. But if prices are identical, you will likely want to opt for the newer SN850X.
Frequently Asked Questions
Does the SN850X/SN850 have DRAM?
Yes, there is an onboard DDR4 DRAM cache/buffer on both the SN850X and SN850 SSDs.
Do I need a heatsink for the SN850X/SN850?
For installation in the PS5, a heatsink is strongly recommended. It doesn't have to be a WD original, however. Gaming PCs typically have integrated motherboard heat spreaders, and in that case, a pre-installed heatsink is not needed.
You can use the SSDs without heatsinks or heat spreaders, but performance may throttle during intensive workloads if the device gets overheated.
What is the life expectancy of an SN850X/SN850?
SSD endurance ratings are specified as TBW (terabytes written or total bytes written) and these values are identical for the SN850 and SN850X lineups. For example, the 2TB models have an endurance rating of 1,200 TBW, meaning that you should be able to write 1,200 TB of data to the drive before memory cells become worn out. This is more than enough to last for the lifetime of most gaming PCs or consoles.
