“Interface an Arduino Mega with an IDE drive or CF Card! It is easier than you might have thought!
The built-in 1 or 4 kilobyte EEPROM memory of an Arduino is quickly used up if you want to permanently store large amounts of data. So it makes sense to connect external mass storage devices in some cases. Fortunately there is already a library and various breakout modules available that allow to connect an SD card to the Arduino. But it is also possible (and not even difficult) to connect CompactFlash and even older hard drives, disk drives or CD- Rom drives to an Arduino Mega. This is due to the fact that CF cards are compatible with the parallel ATA (PATA) specification that was common until 2003. PATA compatible drives are also called IDE drives in common parlance. Unlike SD cards, IDE drives operate at 5V TTL level, so they can be directly connected to the Arduino´s IO Pins.”