WD Black SN850 review: A PCIe 4 powerhouse

A lightning-fast SSD that comes with a selection of great add-ons – and doesn’t cost the earth

A photograph of the WD Black SN850

IT Pro Verdict


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    Outstanding speeds

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    Decent value

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    Useful bundled software


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    Won’t hit top speeds with older systems

If you’re upgrading or building a PC, the WD Black SN850 makes a superb system drive. It takes advantage of the huge bandwidth of the PCI Express Gen4 bus to offer performance rival SSDs can’t match: in our tests it achieved a sequential read speed of almost 6GB/sec, and topped 5GB/sec when writing.

Multi-threaded performance is excellent too. In AS SSD’s 64-thread random-access test, the SN850 kept up a read speed of 2,906MB/sec and a write rate of 2,805MB/sec. In both of the PCMark storage benchmarks it achieved solid first-place rankings, scoring 3,502 in the system disk test and 5,984 as a data disk.

Despite these amazing figures, the SN850 is pretty affordable. True, the 1TB model we tested costs around twice as much as WD’s budget Blue SN550 drive, working out to 18p per gigabyte - but it’s hard to complain about that when you’re getting more than double the performance. There’s also a 500GB model for £80 inc VAT, while the 2TB capacity can be had for £340.

Uniquely, WD also offers variants of all SN850 models with integrated heatsinks to ensure things stay fast and stable during heavy workloads. This adds a lot to the price – the 1TB model costs £234 – and we’re not convinced it’s necessary as the standard drive romped through the intensive PCMark benchmarks without a hitch.

Whichever model you go for, you get a custom edition of Acronis True Image, licensed for five years on both Windows and macOS. It’s an excellent add-on that can simplify the process of cloning your old system drive onto the new SSD, and take care of backups once you’re up and running.

Note that the phenomenal performance of the WD Black SN850 is enabled by the PCI Express Gen4 interface. If you install it in an older PC using PCI Express Gen3 it will still work, but in this configuration we saw read speeds peak at 3,091MB/sec, while the overall system drive score fell to 2,883. At that point, cheaper alternatives like the £114 Kingston KC2500 start to look tempting.

If your motherboard supports PCIe Gen4, however, splash out on the WD Black SN850. It’s the fastest drive around, while the bundled software makes it easy to install and use.

WD Black SN850 specifications

Swipe to scroll horizontally
Cost Per Gigabyte18p
InterfacePCIe 4
Claimed Read2,400MB/sec
Claimed Write1,950MB/sec
Darien Graham-Smith

Darien began his IT career in the 1990s as a systems engineer, later becoming an IT project manager. His formative experiences included upgrading a major multinational from token-ring networking to Ethernet, and migrating a travelling sales force from Windows 3.1 to Windows 95.

He subsequently spent some years acting as a one-man IT department for a small publishing company, before moving into journalism himself. He is now a regular contributor to IT Pro, specialising in networking and security, and serves as associate editor of PC Pro magazine with particular responsibility for business reviews and features.

You can email Darien at darien@pcpro.co.uk, or follow him on Twitter at @dariengs.