Fusion drive works by storing everything on the SSD first. Once the SSD fills up (almost) it starts to move files to the platter drive that are used less often. This makes the Fusion drive faster than Intel's Smart Response Technology.
Intel SRT works by first storing files on the HD, then moving common files to the SSD (cached) drive.
Intel SRT works by first storing files on the HD, then moving common files to the SSD (cached) drive.