Launched on February 2, 2022, the Western Digital WD Black SN770 is a mainstream PCIe 4.0 offering within the company’s gaming-oriented Black lineup. It uses a DRAM-less architecture and is available in capacities ranging from 250GB to 2TB.
As a mainstream PCIe 4.0 SSD, the SN770 targets budget-conscious consumers, particularly gamers looking for an affordable upgrade path from earlier generations of PCIe or SATA. Western Digital markets the drive as delivering up to 40% faster performance and up to 20% more power efficiency compared to its predecessor, the WD Black SN750.
Despite carrying the premium “Black” gaming branding, the SN770 sits in a mid-range or value-oriented segment below the flagship WD Black SN850 and SN850X from the same lineup.
In 2023, a SanDisk-branded (likely) variant of this SSD was released under the name SanDisk Extreme M.2 NVMe (not to be confused with the Extreme Pro from 2018).
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 |
Controller
The SN770 features Western Digital’s proprietary SanDisk controller (model 20-82-10081-A1), also known as Polaris MP16+. This is a 4-channel, tri-core design that Western Digital developed in-house, though the company has been less than forthcoming about specific technical details. In spite of its 4-channel design, the controller enables the drive to run at quite impressive PCIe 4.0 speeds. It supports the NVMe 1.4 protocol and includes features such as multi-step LDPC ECC engine and RAID ECC for data integrity.
DRAM-less Design
To reduce manufacturing costs, the WD Black SN770 uses a DRAM-less design, i.e. without the traditional onboard DRAM cache. Instead, it utilizes Host Memory Buffer (HMB) technology, which leverages up to 64MB of system RAM for storing mapping tables and metadata. This approach was once associated with entry-level drives, but advances in controller technology and firmware optimization have mitigated the traditional performance penalties, to an extent. For write acceleration, the drive uses a dynamic pseudo-SLC cache that varies by capacity: approximately 93GB for 250GB model, 188GB for 500GB, 377GB for 1TB, and 650-740GB for the 2TB variant. Once data is written to the entire SLC cache, the drive falls back to its native TLC NAND performance (approximately 560MB/s).
BiCS5 112-layer TLC NAND
Kioxia and SanDisk (at the time a WD subsidiary) is behind the ubiquitous BiCS5 112-layer 3D TLC NAND flash memory used in the WD Black SN770. This fifth-generation BiCS flash features a quad-plane architecture allegedly offers twice the write performance of its BiCS4 96-layer predecessor. For improved scalability, the NAND uses a circuitry under array (CUA) design that, among other benefits, reduces power consumption by up to 40% compared to previous generations. This variation of the NAND operates at 1,200 MT/s. All capacities use a single NAND package configuration: the 1TB model contains sixteen 512Gb dies in one package, while the 2TB variant uses 1024Gb dies.
Power Consumption
Thanks to the aforementioned improvements, the WD Black SN770 is relatively efficient for a PCIe 4.0 drive, though idle power consumption remains a point of discussion. Under sustained load conditions, power consumption varies by workload but remains lower than many competing 8-channel PCIe 4.0 controllers. The BiCS5 NAND contributes to overall efficiency through its optimized 4KB page read operations. The drive supports standard PCIe Active State Power Management (ASPM) for reduced power consumption in compatible systems, which is particularly beneficial for laptops.
Write Endurance and Over-provisioning
Western Digital rates the SN770’s endurance at industry-standard Total Bytes Written (TBW) metrics, ranging from 200 TBW for the 250GB model up to 1200 TBW at 2TB. These figures equate to approximately 0.33 drive writes per day (DWPD) over the 5-year warranty period for most capacities, but the 250GB model offers slightly higher relative endurance at 0.4 DWPD. The drives come over-provisioned at approximately 9.9%, with 24GB out of 1024GB reserved for controller overhead on the 1TB model. This is to assist with wear leveling, garbage collection, and maintaining performance consistency over the drive’s lifespan.
Professional Reviews
WD’s Black SN770 marks the beginning of an era where SSDs capable of 5GBps speeds are mainstream options, while slower SSDs fall into the budget market… all while utilizing a sleeper of an SSD controller that’s akin to a wolf in sheep’s clothing.
The competitively priced Western Digital WD Black SN770 achieves impressive performance results that match the more expensive Samsung 980 Pro, WD Black SN850, and Kingston KC3000. It seems WD has found a solution to overcome the limitations of DRAM-less designs—very impressive.
It’s taken a while for WD to launch another Gen4 drive into the market, but with the Black SN770 WD has introduced a new controller which is used in combination with BiCS5 TLC NAND to good effect.
WD’s price-competitive Black SN770 PCIe 4 NVMe SSD is a good performer and further evidence that DRAM-less (HMB) design has come of age.
If you are building a mid-range workstation or gaming PC on a limited budget, a 2TB SN770 would definitely be suitable as a primary system drive. Although its maximum sequential performance is not up there with the fastest Gen4 SSDs, it performs well where it counts.
If you’re shopping for an affordable, but high-performance SSD for a new gaming rig, the new WD Black SN770 should definitely be on your short list.
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