AFAIK operating systems delegate reads/writes to their IO subsystem. This subsystem can optimize the IO operations by scheduling them in an order that differs f

AFAIK operating systems delegate reads/writes to their IO subsystem. This subsystem can optimize the IO operations by scheduling them in an order that differs from when they arrived to the IO queue and this improves performance in some cases. Instead of FIFO the subsystem operates on the segment of your storage device that is closest to its current location. Modern IO subsystems are both thread-safe and smarter than the average programmer.