It's not usually the CDROM, but the chipset it's attached to. A lot of recent motherboards have multiple disk controllers -- usually a standard one that's a part of the motherboard chipset, and a second super-shitty one (often from JMicron) so that they can advertise extra ports (also because Intel chipsets didn't support SATA hotplug for the longest time).

It's fairly common for the CDROM in an 'enthusiast' desktop to be attached to the single PATA port on a secondary controller.