Your welcome. Your motherboard has only two IDE slots (Primary slot, Secondary slot). Each IDE cable that goes into the motherboard slots can support 2 IDE devices (hard drives, DVD RWs, CD RWs, Zip drives, or whatever IDE capable devices there are) giving you a total of 4 maximum IDE devices. So you could have 3 CD devices as have mentioned from the thread subject because the other one is used for the hard drive which you must have.
If you have SATA hard drive, you can use all 4 IDE conenctions for your CD ROMs