Integrated Drive Electronic hard drives use master and slave settings to help the computer tell the two devices apart when connected to the same cable. The IDE interface type connects peripheral devices such as hard drives and optical drives to a computer; also referred to as "Parallel ATA" drives, the IDE standard is the more modern Serial ATA device connection standard's predecessor.

Two Devices on One Cable

Master and slave designations are relevant when two devices share the same cable for manually selecting which drive gets which designation. While the names imply the master drive has priority over the slave drive, the only difference between the two is the name. Master and slave refer to "channel 0" and "channel 1" respectively. According to Apple, neither the master or slave drive has any special status or functional difference over the other. Master and slave designations have no bearing on boot priority. The devices will work in any configuration as long as there's not two master drives or two slave drives. According to Seagate, if both drives are configured using the "cable select" setting instead of the master and slave settings, the computer BIOS assigns the master and slave settings based on which cable plug is connected to which device.

Selecting Device Channels

A computer determines if a hard drive is the master or slave depending on the position of the pin jumper next to the cable connection on the drive. Hard drives usually include some sort of diagram on the device as to which pins designate which configuration. When configuring two drives, set the jumper to match the master position from the diagram for one of the drives and set the second drive's jumper to match its slave position from its diagram. The jumper positions vary from device to device and should be considered independent for the hard drive. Jumpers can be removed and re-positioned by hand or with tweezers.

Setting Up the Drives

The computer case must be opened to configure the hard drives; only work inside a computer with the power off and after donning a static-resistant wrist strap or at least touching metal to discharge any static in your body.

The hard drive jumpers can be difficult to work with if the hard drives are already installed in the computer's case, so remove the hard drives from the case if necessary. The configuration order is: set the jumpers, install the hard drives in the bay, connect the IDE cable to the motherboard and connect the IDE cable to the hard drives.

Drive Management Best Practices

IDE hard drive management best practices include connecting as few devices to a cable as possible and using the master setting for devices with a dedicated cable.
A single hard drive on a dedicated cable will work exactly the same if its set as slave or master; however, setting the drive to master avoids having to change the settings when adding a secondary slave drive later. Master and slave settings are useful for older systems that don't support cable select settings or when only one device supports cable select.