The MX25R6435FZAIH0 is a 64Mbit (8MB) ultra-low-power SPI NOR Flash from Macronix in WLCSP-24 (1.45×1.95mm), operating from 1.65V to 3.6V with dual/quad SPI support. The R-series (MX25R) is optimized for ultra-low power consumption: active read current is 4mA at 85MHz (vs 15mA for the standard MX25L series), and deep power-down current is only 0.5uA. The dual-supply-range architecture provides two performance modes: 1) High-performance mode (1.65-3.6V): 133MHz clock, fast read with 4 dummy cycles; 2) Ultra-low-power mode (1.65-1.95V): 33MHz clock, reduced current. The mode is selected by the RSTEN/RSTM command sequence. Memory is organized as 128 sectors of 64KB, each with 256 pages of 256 bytes. The 4KB sub-sector erase enables fine-grained updates. Quad SPI (QPI) mode uses all four IO pins for command, address, and data transfer, achieving 4x throughput for code shadowing. The WLCSP-24 package uses 0.4mm pitch bumps, providing the smallest possible footprint for space-constrained designs like wearables, hearables, and IoT sensors. The -I suffix denotes industrial temperature range (-40C to +85C). Security features include OTP area and 3×256-byte security registers with unique ID.