CF cards can operate in three modes: memory mode, PC Card/IO mode, and IDE/fixed disk mode. Since CF cards were originally a type of portable storage for camera

CF cards can operate in three modes: memory mode, PC Card/IO mode, and IDE/fixed disk mode. Since CF cards were originally a type of portable storage for cameras, etc., it makes sense for them to be treated as removable devices. One would plug it into a computer, download the files, then eject the card. The OS would like to know its removable so it can make any writes immediately and not buffer or cache them like it might do for a fixed disk. Some cards, usually marketed as "industrial", support a fixed disk mode. This one for example can be set to fixed disk by grounding pin 9 (output enable): [PDF] https://resources.winsystems.com/datasheets/cflash-g-xxxm-i-ds.pdf https://resources.winsystems.com/datasheets/cflash-g-xxxm-i-...