The Fusion Drive system in these iMacs consists of a standard SATA HDD and a smaller cache SSD located separately on the board (generally anywhere from a 32GB to 128GB drive depending on the total Fusion Drive size). Since the SSD acts only as a cache for frequently accessed data, the standard SATA HDD will have the entire file system on it at all times, and the SSD will only contain duplicated data that the system deems necessary for faster access. Assuming that SATA HDD is not dead or defective, data extraction just requires removing that one drive and connecting it to another computer with a standard SATA data/power cable. With these iMacs, that process is the easiest one, as removing the SSD requires removal of the entire logic board, while the standard HDD can be accessed immediately after removing the LCD panel.