Well.. the HD led should light up anyway so I guess it could be a HD/CD indicator. There are a few IDE splitters available that gives the option of adding a indication led for the second IDE chain. If you keep the HD on the first IDE chain and the CD on the second and then that led would do it I think. While you're at it with adding leds to the machine you should concider adding a PCMCIA Activity led aswell (great for when you use a PCMCIA Ethernet card).