As of 2019, the nRF52840 is the most advanced SoC of Nordic Semiconductor's nRF52 line. The nRF52840 packs a 32-bit ARM Cortex-M4F at 64MHz with 1MB of NOR flash and 256KB of RAM accessible via its AHB (AMBAv2). 9 distinct AHB slaves are (non-uniformly) connected to memory, and 2 to flash (one to each of data and instruction cache). 3 SPI and 1 QSPI interfaces run at up to 32MHz.
The device cannot support flash pages greater than 512KB in size using its QSPI peripheral.