During the last 20 years an interface IDE (ATA) was used to connect hard disks and CD/DVD-drives, and only during the last years it was changed to Serial ATA (SATA). But all motherboards have one or two connectors to connect IDE-devices together with SATA connectors. The connectors are designated as Primary IDE and Secondary IDE, and they are able to be connected with no more than two IDE-disks by using a loop: the first disk is called Master and the second is Slave. Thus, if you have two connectors, you can connect no more than four devices which would be designated as Primary Master, Primary Slave, Secondary Master and Secondary Slave.
Each IDE-device is equipped with special jumpers with the help of which the configuration Master or Slave is chosen. There is usually a sticker with instructions how to do this correctly on the device case; there also might be symbols directly in the place of jumpers setting. If you connect two devices to one loop, one of them must be configured as Master, another – as Slave. In other case, both devices, most likely, would not operate. All modern motherboards have several SATA connectors, and it is much easier to connect the drives of this standard as they configure automatically. But after the connection of new disks your operating system may not boot and then you must set the boot sequence.
The parameters for hard disks setting are traditionally concentrated in the section “Standard CMOS Features” (or Main – for versions of BIOS with horizontal menu bar). Each device is usually set in a separate sub-menu with the name of channel to which the disk has been connected.