The Western Digital WD Black SN850 is a high-end M.2 NVMe solid-state drive (SSD) released in October 2020, taking aim at gaming and professional workstation applications. As Western Digital’s first PCIe 4.0 consumer SSD, it offers significant improvements over its predecessor, the WD Black SN750, offering substantially improved overall performance.
The WD Black SN850 was positioned as a flagship gaming SSD, competing directly with the Samsung 980 PRO and drives based on the Phison E18 controller. Western Digital marketed the drive specifically toward PC gamers and creative professionals requiring high-speed storage, with particular emphasis on reduced game loading times and improved system responsiveness. The SN850 was among the first SSDs officially compatible with the PlayStation 5 console when Sony enabled M.2 expansion support, requiring drives capable of at least 5,500 MB/s sequential read speeds.
Specifications
| Specification | 500GB | 1TB | 2TB |
|---|---|---|---|
| Model Number (Standard) | WDS500G1X0E-00AFY0 | WDS100T1X0E-00AFY0 | WDS200T1X0E-00AFY0 |
| Model Number (Heatsink) | WDS500G1XHE-00AFY0 | WDS100T1XHE-00AFY0 | WDS200T1XHE-00AFY0 |
| Interface | PCIe Gen4 x4, NVMe 1.4 | PCIe Gen4 x4, NVMe 1.4 | PCIe Gen4 x4, NVMe 1.4 |
| Sequential Read (MB/s) | 7,000 | 7,000 | 7,000 |
| Sequential Write (MB/s) | 4,100 | 5,300 | 5,100 |
| Random Read IOPS (4K QD32) | 810,000 | 1,000,000 | 1,000,000 |
| Random Write IOPS (4K QD32) | 680,000 | 720,000 | 710,000 |
| Controller | WD Black G2 (SanDisk 20-82-10035-A1) | WD Black G2 (SanDisk 20-82-10035-A1) | WD Black G2 (SanDisk 20-82-10035-A1) |
| NAND Type | 96-layer BiCS4/BiCS5 3D TLC | 96-layer BiCS4/BiCS5 3D TLC | 96-layer BiCS4/BiCS5 3D TLC |
| DRAM Cache | 512MB DDR4 | 1GB DDR4 | 2GB DDR4 |
| SLC Cache (Dynamic) | ~138GB | ~277GB | ~554GB |
| Endurance (TBW) | 300 | 600 | 1,200 |
| Form Factor | M.2 2280 (80 x 22 x 2.38mm) | M.2 2280 (80 x 22 x 2.38mm) | M.2 2280 (80 x 22 x 2.38mm) |
| Weight (Standard) | 7.5g ± 1g | 7.5g ± 1g | 7.5g ± 1g |
| Dimensions (Heatsink) | 80 x 23.4 x 8.8mm | 80 x 23.4 x 8.8mm | 80 x 23.4 x 8.8mm |
| Warranty | 5 years limited | 5 years limited | 5 years limited |
Controller
Western Digital’s proprietary second-generation “WD Black G2” controller (officially designated as SanDisk 20-82-10035-A1) is 8-channel design manufactured in-house. This controller is a complete redesign from the first-generation controller used in the SN750, as it’s created for PCIe 4.0 interface speeds. The controller features improved low queue-depth performance optimization and implements Western Digital’s nCache 4.0 technology, a hybrid SLC caching system designed to maintain consistent performance across different workloads.
Cache Architecture
Each model of the SN850 includes DDR4 DRAM at a ratio of 1GB per 1TB of storage capacity for mapping table storage. The nCache 4.0 implementation features both static and dynamic SLC caching, with the dynamic portion comprising approximately one-third of the drive’s available capacity (meaning about 277 GB on the 1TB model). A smaller static SLC cache (approximately 12 GB) provides immediate write acceleration that quickly recovers during idle periods.
NAND Type and Specifications
The SN850 is equipped with 96-layer 3D TLC NAND flash memory, specifically BiCS4 (later production runs used BiCS5) manufactured by Kioxia (formerly Toshiba Memory). All models use a single-sided M.2 2280 form factor design, allowing compatibility with thin laptops and systems with limited clearance. The flash memory operates with a multi-gear Low-Density Parity-Check (LDPC) error correction engine, providing RAID-like protection for full multi-page recovery, internal SRAM ECC, and end-to-end data path protection.
Power Consumption
Active idle power consumption measures approximately 1W, while the deepest idle state (PS4) reduces power draw to approximately 35mW. During sustained writes, the drive consumes approximately 6.6W on average, with peak power draw reaching up to 8.8W under maximum load. The drive implements full APST (Autonomous Power State Transition) support for automatic power management in compatible systems.
Write Endurance and Over-Provisioning
Western Digital rates endurance using industry-standard TBW (Terabytes Written) metrics based on JEDEC client workload specifications (JESD219). The drives feature about 9% over-provisioning to maintain performance consistency and enhance longevity.
All capacities include an industry-standard 5-year limited warranty, with coverage ending at either the warranty period or the rated TBW limit, whichever occurs first.
Other Noteworthy Features
- Game Mode: Available through the WD_BLACK Dashboard software (Windows only), this feature disables low power states to minimize latency during gaming sessions
- Optional Heatsink: Include an aluminum heatsink with customizable RGB lighting controllable via the Dashboard software
- PlayStation 5 Support: Officially compatible with PS5 system software version 21.02-04.00.00 or higher (heatsink model recommended)
- Acronis True Image: Free cloning and backup software included with purchase
Professional Reviews
The WD Black SN850’s overall performance on the mixed random IO test is just behind the Samsung 980 PRO, but still very good for a flash-based SSD.
The WD Black SN850 is the fastest SSD we ever tested thanks to support for the fast PCI-Express 4.0 interface.
The SN850 is an excellent release by the company for pretty much any consumer application… specifically a dominating performance in read activity.
The new drive is the company’s first foray into the PCIe Gen 4 market segment… and it’s a cracker!
GamingPCBuilder – Comparison with successor WD Black 850X
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