128 Mbit density and the 133 MHz Quad I/O read ceiling
The S25FL128SAGMFBG00: Organized as 16M x 8, the 128 Mbit capacity holds a full firmware image plus a file system partition for an automotive ECU or an industrial controller — the 133 MHz SPI clock with Quad I/O reads at a sustained throughput of roughly 66 MB/s, fast enough for execute-in-place code shadowing without stalling the core. The Quad I/O interface reduces the pin count to six signals (CS, CLK, IO0-IO3) compared to a parallel NOR flash, saving board space and routing layers on a 16-SOIC footprint.