108 MHz Quad I/O — what the speed rating means for the design
The 108 MHz clock rate applies to the SPI interface in both standard and Quad I/O modes. In Quad I/O, the effective read bandwidth approaches 54 MB/s (108 MHz × 4 bits), which is enough to support execute-in-place (XIP) from the Flash for many MCUs without stalling the core. The write-cycle time of 3 ms per word or page is typical for NOR Flash of this generation — adequate for field updates but not for high-frequency logging. The 64 Mbit density gives roughly 8 MB of non-volatile storage, suitable for a single firmware image plus a small filesystem or a pair of redundant images for fail-safe OTA.