WD Polaris MP16

The WD Polaris MP16 (full designation: 20-82-01008-A1) is Western Digital's in-house NVMe controller used in the WD Blue SN550, targeting the mainstream PCIe 3.0 value segment. It is a triple-core ARM 32-bit Cortex-R design manufactured on TSMC's 16nm FinFET process, with 4 flash channels running at 1,200 MT/s and 4 chip-enables per channel.

The Polaris MP16 is a DRAM-less controller that relies on Host Memory Buffer (HMB), borrowing a portion of system RAM to cache the flash translation layer, rather than dedicated on-drive DRAM. This keeps drive cost and idle power draw down while avoiding the worst random-read latency penalties of fully buffer-less designs. The SN550 and SN570 are 4-channel drives, reflecting the controller's mainstream positioning. The higher-performance Polaris MP16+ followed with PCIe 4.0 support, used in the WD Black SN770 and WD Blue SN580.