128 Mbit Quad-SPI NOR — the 125°C workhorse
Its headline trick is the Quad I/O interface running at 133 MHz, which pushes read throughput past 66 MB/s without adding pins beyond the standard SPI footprint. That matters when you're doing execute-in-place from flash on a tight PCB layout. That 125°C ceiling is the differentiator versus the 105°C siblings in the same FL-S family — this one keeps working in an engine bay or a hot industrial cabinet where the 105°C parts would be marginal.
125°C rating — not just a spec sheet number
Most of the FL-S 128 Mbit parts (S25FL128SAGMFV010, S25FL128SAGMFV001, S25FL128SAGMFB000) are specced to 105°C. That's the difference between a part that derates in a sealed enclosure at 85°C ambient and one that still meets timing at 105°C junction. If your thermal analysis shows junction temps above 105°C, this is the FL-S variant to quote.