The IDE (Integrated Drive Electronics) interface is a standardised storage interface bourne out of the collection of competing and limiting standards in the early 90s. The ST-506 interface was cumbersome, requiring detailed knowledge of a hard disk's internals such as the number of heads and tracks/cylinders, and it could be tedious trying to match a CD drive and controller when either could be Matsushita MKE, Mitsumi or Sony (all of which were incompatible). When IDE and ATAPI were introduced, the installation process for both hard disks and CD drives was greatly simplified.
IDE allows the connection of up to two devices per bus, with one designated the master and the other the slave. Typically this is set via jumpers next to each device's IDE connector, however in the late 90s cable-select became common which would configure devices as master/slave depending on their location on the cable. This however required cables that supported the cable-select signals, so it only became practical once UDMA66 introduced 80-conductor cables, as support for cable-select was not guaranteed with earlier 40-conductor cables.
Cable select is implemented by the host adapter connecting pin 28 to GND. If a device sees pin 28 grounded, it will assume the master role. If it sees pin 28 is left floating (not connected) then it will assume the slave role. Thus a cable-select-compatible IDE cable will omit the connector for pin 28 on the connector designated to be the slave.
OAKCDROM.SYS is typically used as it works with many IDE CD drives. It must be loaded in CONFIG.SYS to provide the low-level CD driver. MSCDEX.EXE is then loaded to provide a drive letter for the CD.
These devices provide an IDE interface.