MSI MS-5191 Manual page 23

The mainboard has a 32-bit Enhanced PCI IDE Controller that provides
two HDD connectors IDE1 (Primary) and IDE2 (Secondary). You can
connect up to four hard disk drives, CD-ROM, 120MB Floppy and other
devices to IDE1 and IDE2.
IDE1(Primary IDE Connector)
The first hard disk should always be connected to IDE1. IDE1
can connect a Master and a Slave drive.
IDE2(Secondary IDE Connector)
IDE2 can connect a Master and a Slave drive.
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