PC Repair and Maintenance: A Practical Guide (Charles River Media Networking/Security)

All standard PC motherboards today come with two EIDE channels, primary and secondary, as evidenced by connectors on the board. Each channel can handle two EIDE devices, one as the master and one as the slave. In this context, the terms master and slave really don't mean much, as everything a master drive can do, a slave drive can do also, although traditionally, the hard drive with the OS/boot files is installed as the primary master. This is not a rule, however. If the BIOS is set to detect any device as a boot device, then any one of the four can have the OS. The only restriction is that each channel cannot have more than one master and one slave drive. EIDE devices that can be connected to the EIDE connectors include hard drives, optical drives (CD and DVD), and Zip drives. Additional EIDE drives can be added to motherboards by using an EIDE expansion card (one manufacturer is Promise Technology, Inc. at promise.com). To use SCSI devices, a SCSI controller expansion card must be installed.

As we said before, many newer boards come with SATA connectors as well. With this interface, there is no such thing as master and slave, and only one device can be attached to each SATA connector.