The WD_BLACK SN850X 4TB is the high-capacity flagship in WD’s Gen 4 NVMe line — for buyers who want both the SN850X’s top-tier speeds and a much larger single-drive capacity. At around $329 it pairs sequential reads up to 7,300 MB/s with a DRAM-backed controller, BiCS 5 TLC, Game Mode 2.0 firmware and 4TB of capacity. This is one of the most popular single-drive choices for serious enthusiasts who want to consolidate their gaming and creative storage onto one fast NVMe SSD. This WD_BLACK SN850X 4TB review covers the speeds, DRAM cache and endurance, real-world use, PS5 compatibility, value and verdict.
WD_BLACK SN850X 4TB NVMe SSD - M.2 2280, Up to 7,300 MB/s Read speeds, Up to 6,300 MB/s write speeds, Gaming Expansion, High Performance Internal Solid State Drive - WDS400T2X0E
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Quick answer: Our top pick in 2026 is the Form factor — our #1 rated choice. See the full ranked comparison, alternatives and buying advice below.
WD_BLACK SN850X 4TB at a Glance
| Component | Specification |
|---|---|
| Form factor | M.2 2280, double-sided at 4TB |
| Interface | PCIe 4.0 x4 NVMe |
| Capacity | 4TB (also 1TB, 2TB and 8TB) |
| Sequential read | Up to 7,300 MB/s |
| Sequential write | Up to 6,600 MB/s |
| Random read IOPS | Up to 1,200K (4K QD32) |
| DRAM cache | Yes — LPDDR4 DRAM |
| NAND type | BiCS 5 3D TLC |
| Warranty | 5-year limited / 2,400 TBW for 4TB |
| Approx price | around $329 |
Speeds & Performance
The 4TB SN850X delivers the same flagship sequential numbers as its smaller siblings — up to 7,300 MB/s read and 6,600 MB/s write — and benefits from having more NAND dies to parallelise writes across, which keeps sustained write performance very strong. Random reads are around 1,200K IOPS. In day-to-day use this is one of the most capable consumer SSDs you can buy.
Real-world feel is excellent: fast Windows boots, near-instant game loads, slick DirectStorage texture streaming. WD’s Game Mode 2.0 firmware adds gaming-tuned optimisations on top of the strong baseline. For an enthusiast who wants both top-tier speed and large capacity in a single drive, the SN850X 4TB is a strong pick. See our best NVMe SSDs for gaming guide for cross-rival comparisons with the Samsung 990 PRO 4TB.
WD also has a long manufacturing-quality reputation behind the WD_BLACK brand specifically. The line is built to the company’s tightest consumer tolerances, supported by WD_BLACK Dashboard monitoring software with firmware updates, drive-health metrics and a one-click Game Mode toggle. For a 4TB drive likely to host a years-spanning library, that ecosystem matters as much as the raw specs.
DRAM Cache & Endurance
The 4TB SN850X uses WD’s in-house controller paired with LPDDR4 DRAM cache — full DRAM-backed design that keeps random write performance and 4K latency excellent under sustained mixed workloads. The BiCS 5 TLC flash is mature, and the larger 4TB NAND array gives the drive more SLC cache headroom than smaller capacities, which translates to longer sustained write windows under heavy load.
Endurance is rated at 2,400 TBW over a 5-year limited warranty — twice the 2TB rating and more than any realistic gaming or creative workload will exhaust. The main fitment caveat is that the 4TB SN850X is double-sided, which can foul cooling or fitment in very slim laptops or compact small-form-factor builds. Check clearance before buying. The combination of in-house WD controller, BiCS 5 NAND from the Kioxia-WD joint venture and the long-running Game Mode firmware development gives the SN850X one of the most cohesive end-to-end engineering stacks in consumer storage.
Gaming & Workstation Use Cases
For gaming, the 4TB capacity is genuinely transformative — modern AAA games regularly run 100-200 GB each, and 4TB comfortably holds a very large library installed at once with no juggling. DirectStorage performance is excellent and texture streaming is smooth. This is the drive for buyers who want to keep their entire active library installed and never have to delete anything.
For workstation use, 4TB at SN850X speeds is one of the best capacity-and-performance combinations available. A single drive can hold large 4K and 8K video projects, RAW photo libraries, AI model files and active development repositories with room to spare, all running at flagship Gen 4 speeds. For a gamer-creator or a single-drive workstation, this is one of the strongest picks. For build pairings see our gaming PC build guide.
Compared with running two 2TB drives in parallel, a single 4TB SN850X gives you simpler storage management, one slot used instead of two, and no risk of mismatched performance between drives. The trade-off is the absolute price — 4TB drives cost more in one purchase than 2x 2TB — but for users who value a clean single-drive build, the convenience is real.
PS5 Compatibility & Heatsink
The 4TB SN850X exceeds the PS5’s 5,500 MB/s read requirement and fits the console’s M.2 expansion slot. 4TB is particularly attractive for PS5 owners because the console’s own internal storage fills quickly — a 4TB expansion effectively quadruples usable PS5 storage and lets you keep a substantial library installed.
Sony requires a fitted heatsink. WD offers an SN850X 4TB Heatsink variant designed to fit the PS5; alternatively, fit a separate heatsink from our best M.2 SSD heatsinks roundup. For Sony-licensed PS5 storage see the WD_BLACK SN850P in our best PS5 expansion SSD guide.
Value & Price Per TB
At around $329 for 4TB, the SN850X works out to roughly $0.082 per gigabyte — competitive with the Samsung 990 PRO 4TB and meaningfully better $/GB than the 1TB and 2TB capacities. For buyers who want flagship speed combined with large capacity in a single drive, the 4TB is the right sweet spot — more capacity per drive but at a higher absolute price than 2TB, and better $/GB than the 1TB. WD also runs aggressive seasonal promotions across the SN850X line, and 4TB capacities are often the most steeply discounted during major sales events.
Verdict
The WD_BLACK SN850X 4TB is one of the best high-capacity Gen 4 NVMe SSDs you can buy. It pairs flagship speeds with full DRAM cache, Game Mode 2.0 firmware, a 5-year warranty and the kind of capacity that lets you stop juggling games and project files entirely. The only caveat is the double-sided design at 4TB. For an enthusiast gaming PC, a single-drive creative workstation or a serious PS5 expansion, it earns a clear recommendation. Compare flagship 4TB options in our best NVMe SSDs for gaming guide, and consider the heatsink variant if you need PS5 fitment or if your build lacks motherboard M.2 cooling.
Frequently Asked Questions
Is the SN850X 4TB worth the price?
For enthusiast buyers, yes. Flagship Gen 4 speeds combined with 4TB of capacity in a single drive is a strong combination, and the per-gigabyte price is competitive at this tier.
Is the SN850X 4TB single-sided or double-sided?
The 4TB SN850X is double-sided to fit the higher capacity. This is normal at 4TB but may foul fitment in very slim laptops or compact small-form-factor builds — check clearance before buying.
Does the SN850X 4TB work in PS5?
Yes. It exceeds the PS5’s 5,500 MB/s read requirement and fits the M.2 expansion slot. Use the heatsink variant or fit a separate heatsink to meet Sony’s requirements.
How does the SN850X 4TB compare with the 990 PRO 4TB?
They are very close — both are top-tier 4TB DRAM-backed Gen 4 drives with similar real-world performance. Pick on price, brand preference and which heatsink/PS5 variants you need.
More NVMe SSD Reviews
- WD_BLACK SN850P 2TB Review: PS5 Licensed Storage Expansion
- WD_BLACK SN7100 2TB Review: Compact Gen 4 NVMe SSD
- Crucial P310 1TB Review: Compact Gen 4 NVMe SSD (7,100 MB/s)
- Samsung 9100 PRO 1TB Review: PCIe Gen 5 NVMe SSD (2026)
- Samsung 990 PRO 4TB Review: Flagship Gen 4 NVMe SSD
- Samsung 990 PRO 2TB Review: Premium Gen 4 NVMe SSD
- Samsung 990 PRO 1TB Review: Premium Gen 4 NVMe SSD
- Samsung 990 EVO Plus 1TB Review: Gen 4×4 / Gen 5×2 NVMe SSD
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