@sanjyuubi, post #858
@perinoid, post #857
@sanjyuubi, post #858
In the ATA standard, pin 20 is defined as (mechanical) key and is not used. This socket on the female connector is often obstructed, requiring pin 20 to be omitted from the male cable or drive connector, making it impossible to plug it in the wrong way round; a male connector with pin 20 present cannot be used. However, some flash memory drives can use pin 20 as VCC_in to power the drive without requiring a special power cable; this feature can only be used if the equipment supports this use of pin 20.
@micromars, post #864