Western Digital WD_BLACK SN850P 2TB vs Western Digital WD_BLACK SN850X 2TB
On the measures that settle this, Western Digital WD_BLACK SN850X 2TB never comes out behind, and on at least one it comes out ahead.
| Specification | Western DigitalWD_BLACK SN850P 2TB | Western DigitalWD_BLACK SN850X 2TB |
|---|---|---|
| Capacity (GB) | 2000 | 2000 |
| Sequential read (MB/s) | 7300 | 7300 |
| Sequential write (MB/s) | 6600 | 6600 |
| Current best price | £309.99at Amazon.co.uk · captured 2026-09-13 | £305.23betterat Amazon.co.uk · captured 2026-09-13 |
| Price per TB | £155.00 | £152.62better |
| DRAM cache | Yes | Yes |
| NAND type | tlc | tlc |
| Controller | — | Western Digital in-house 8-channel controller |
How these two compare
Sequential throughput
Western Digital WD_BLACK SN850P 2TB is rated 7300 MB/s read and 6600 MB/s write; Western Digital WD_BLACK SN850X 2TB, 7300 MB/s read and 6600 MB/s write. These are peak sequential rates over PCIe — the speed you would see copying one large file. For boot, app launches and everyday feel, random access matters more than this headline figure.
Price
Western Digital WD_BLACK SN850P 2TB lists at £309.99, or £155.00 per TB; Western Digital WD_BLACK SN850X 2TB at £305.23, or £152.62 per TB.
DRAM cache
Western Digital WD_BLACK SN850P 2TB carries a DRAM cache; Western Digital WD_BLACK SN850X 2TB carries a DRAM cache. A DRAM cache holds the drive's mapping table — the index of where each block physically sits — so the controller places and finds data without an extra flash lookup. A DRAM-less drive borrows a little system memory (HMB) or a slice of its own flash instead, and is likelier to slow once a long run of random writes outlasts its fast cache.
NAND, controller and warranty
NAND: Western Digital WD_BLACK SN850P 2TB uses TLC and Western Digital WD_BLACK SN850X 2TB uses TLC. The tier is bits per cell — SLC, MLC, TLC and QLC from one to four — trading density against endurance and sustained-write speed: QLC is cheapest per gigabyte, TLC the mainstream balance, and the denser the cell the sooner sustained writes taper. On the controller: Western Digital WD_BLACK SN850P 2TB's controller is not stated, and Western Digital WD_BLACK SN850X 2TB uses the Western Digital in-house 8-channel controller. It is the chip handling error correction, wear-levelling and where each write lands — much of how a drive holds up under load — even if the part number on its own tells you little. On the cover: Western Digital WD_BLACK SN850P 2TB does not state one, Western Digital WD_BLACK SN850X 2TB carries a 5-year warranty. The length is the maker's own vote of confidence, and on an SSD it tends to track the endurance rating — a longer warranty usually meaning more rated writes.
Which to buy
Western Digital WD_BLACK SN850X 2TB. It gives up nothing to the other on the measures the site tracks and leads on at least one, so there is no trade to weigh — the sections above show where the margin is.
Common questions about this pair
- Which is faster, Western Digital WD_BLACK SN850P 2TB or Western Digital WD_BLACK SN850X 2TB?
- Western Digital WD_BLACK SN850P 2TB is rated 7300 MB/s read and 6600 MB/s write; Western Digital WD_BLACK SN850X 2TB, 7300 MB/s read and 6600 MB/s write. These are peak sequential rates over PCIe — the speed you would see copying one large file. For boot, app launches and everyday feel, random access matters more than this headline figure.
- Which costs less per terabyte, Western Digital WD_BLACK SN850P 2TB or Western Digital WD_BLACK SN850X 2TB?
- Western Digital WD_BLACK SN850P 2TB lists at £309.99, or £155.00 per TB; Western Digital WD_BLACK SN850X 2TB at £305.23, or £152.62 per TB.
- Should you buy Western Digital WD_BLACK SN850P 2TB or Western Digital WD_BLACK SN850X 2TB?
- Western Digital WD_BLACK SN850X 2TB. It gives up nothing to the other on the measures the site tracks and leads on at least one, so there is no trade to weigh — the sections above show where the margin is.