What is the difference between master IDE and slave IDE?

Each IDE slot can handle two drives. One drive will be the master and the other will be the slave depending o the configuration. If the jumpers of one drive is configured to set the drive as MA (Master), the second must be configured to SL (Slave). Both drives may be configured as CS (Cable Select), if so, The positioning on the ribbon cable will determine whic one is the master and which is the slave