I don't think there is one honestly. Not for the mini cd's, I know what you're referring to. Usually they rest in a small area shaped for them when a drive is mounted horizontally, but there are no retention slots that far in. Many will have very short 'tabs' that will create a tiny groove for full sized discs to rest in for a vertical mounted drive. The solution if the person really wants the 540 air and needs drivers that come on a mini disc is to instead go to the manufacturer's website and download the drivers. Far easier than the other option which is to use a different system with a horizontal drive, copy the mini disc, transfer it to a full size cd and then use it that way - or opting for a usb external cd/dvd rom.