Jesper Berg 
The WD_Black SN770 was released in 2022 and quickly became one of the most popular M.2 SSDs among PC builders and upgraders. Although it lacks DRAM and targets the mainstream market with a reasonable price tag, it greatly impressed testers by surpassing high-end SSDs like the Samsung 980 Pro in certain real-world-oriented workloads.
Later in 2022, Western Digital added the SN850X to its lineup – an updated version of the SN850 from early 2021. This drive, on the other hand, is clearly positioned at the high-end and comes with far more impressive specs as well as onboard DRAM.
At the time of writing (2023), NAND and SSD prices have dropped further and brought the SN770 and SN850X closer together in terms of pricing. If you are undecided between the two ahead of a storage upgrade or a new build, here’s how they differ according to our data.
SN770 Vs. SN850X: Specifications
For the sake of simplicity, this table features the 2TB capacities of the SN770 and SN850X, respectively. You can view the specifications of each capacity in the respective lineups further down on this page.
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If you go by the specifications alone, the SN850X appears significantly faster than the SN770 in every area that directly relates to performance. The SN770 tops out at just over 5,000 MB/s in sequential transfer rates, while the SN850X practically maxes out the PCI-Express 4.0 x4 interface. A similar gap can be seen in the random read/write IOPS area.
Of course, the SN770 also has no onboard DRAM buffer but instead uses a share of the system’s RAM in the form of a so-called host memory buffer (HMB).
There are also some similarities, not least that both of these SSDs use the same NAND Flash memory chips of the high-end TLC (triple-level cell) variety. Most likely, they also share some aspects of the proprietary SSD controller. Last but not least, the endurance ratings and warranty terms are identical.
SN770 Vs. SN850X: Performance
As we’ve learned from testing SSDs through the years, spec sheets are not necessarily indicative of how a drive performs in a real-world setting. Note that our testing is done with the largest capacities of each drive, meaning the 2TB SN770 and 4TB SN850X. The performance of the 4TB SN850X is however rated as identical to the 2TB capacity.
AS SSD
Sequential performance with AS SSD is typically well below the specified maximum rates. In relative terms, it is still quite on the mark, with the SN850X being about 35% faster than the SN770.
CrystalDiskMark
A similar gap can be seen in CrystalDiskMark, where sequential transfer rates tend to be closer to the “up to” numbers.
Random 4K Q1T1 data is better at predicting general performance in everyday tasks. Here, the difference is much smaller, and the SN850X is less than 20% ahead of its midrange sibling.
Latency/Response Time
Latency in microseconds, as measured with Anvil’s Storage Utilities, is again better with the SN850X but only by an insignificant amount in the 4K write area.
SN770 Vs. SN850X: Gaming Performance
In actual games, SSD performance usually becomes less of a factor unless DirectStorage is involved.
The combined loading times in the Final Fantasy 14: Shadowbringer benchmark (five levels) see the SN850X coming out ahead of the SN770 by 1,6 seconds – an 18% reduction in load times.
UL’s 3DMark Storage Benchmark measures the average bandwidth utilized in gaming workloads like installing, copying, loading, and recording games. It places the SN850X in the lead by about 22% over the SN770 in our runs.
Conclusion
We have previously concluded that the SN770 is very fast compared to other DRAM-less SSDs – especially entry-level models like the Kingston NV2. However, there is also no question that DRAM still makes a difference to overall performance, and that the WD_Black SN850X is a substantially faster SSD.
Read more:
- Comparison of the WD_Black SN850X Vs. SN850 (non-X)
- Full review of the SN770
- Full review of the SN850X
- Updated listing of the best M.2 SSDs
- Updated listing of the fastest SSDs overall (incl. SATA)
SN770 Lineup: Full Specifications
| WD Black SN770 | 250GB | 500GB | 1TB | 2TB |
|---|---|---|---|---|
| Form Factor | M.2 2280 | 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 | PCIe 4.0 x4 / NVMe 1.4 |
| Controller | Proprietary | Proprietary | Proprietary | Proprietary |
| DRAM | No | No | No | No |
| Memory | 112-Layer TLC | 112-Layer TLC | 112-Layer TLC | 112-Layer TLC |
| Sequential Read | 4,000 MB/s | 5,000 MB/s | 5,150 MB/s | 5,150 MB/s |
| Sequential Write | 2,000 MB/s | 4,000 MB/s | 4,900 MB/s | 4,850 MB/s |
| Random Read | 240K IOPS | 460K IOPS | 740K IOPS | 650K IOPS |
| Random Write | 470K IOPS | 800K IOPS | 800K IOPS | 800K IOPS |
| Endurance | 200 TBW | 300 TBW | 600 TBW | 1,200 TBW |
| Warranty | 5-Years | 5-Years | 5-Years | 5-Years |
| MSRP | $59.00 | $79.00 | $129.00 | $269.00 |
SN850X Lineup: Full 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 |
