In simpler form....
The categories and numbers are sybolic changes for the old Master / slave designation for the position of a drive.
IDE/IEDE is the 40 pin connection (interface connection) on the motherboard for connecting the 40 or 80 wire cable. The channel designation is the replacement of the master/slave designation. where channel 1 is the end of cable connection (master) and channel 2 is the middle cable connection (slave).
This is only for location purposes now as the newer boards and BIOS settings will recognize drives from any of the positions and determine the master / slave as set from the jumpers of the drive...
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