Samsung 990 Pro vs WD Black SN850X

Both drives sit at the top of the PCIe 4.0 class: the 990 Pro quotes up to 7450/6900 MB/s read/write and the SN850X up to 7300/6600. The paper gap is under 3%, and both saturate the interface in benchmarks.

In OS boots, game level loads and application launches the two are indistinguishable in blind testing, usually trading results inside the margin of error. No user would notice which drive was installed in daily use.

Both carry a full DRAM cache and a competent controller, but the 990 Pro's more efficient controller holds write speed a little longer once its pSLC cache fills - visible in multi-hundred-gigabyte transfers. For the small random writes of an OS drive, the difference is negligible.

Both 2TB models are rated around 1200 TBW and carry five-year warranties. Neither has a meaningful endurance advantage for normal use, where reaching that rating would take years of unusually heavy writing.

The SN850X is usually the cheaper of the two at the same capacity and goes on sale more aggressively. Given the near-identical performance, the discount at checkout decides the purchase more often than any specification.