It uses a Quad I/O SPI interface running at 133 MHz clock frequency, giving the designer a straightforward way to increase read throughput without migrating to a parallel NOR interface or adding extra pins.
133 MHz Quad I/O — what it means for read bandwidth
At 133 MHz in Quad I/O mode, the S25FL128SAGMFVR03 delivers a sustained read throughput that keeps a Cortex-M4 or similar MCU fed during code shadowing without wait-state bottlenecks. The Quad I/O interface uses four data lines for both address and data, so the effective throughput is roughly four times that of a single-bit SPI at the same clock rate. This matters when the design executes firmware directly from the Flash (XIP) or loads large lookup tables at boot.