The US Patent & Trademark Office has just after publishing a patent application Apple filed on May 2006, titled "Memory Disc Adaptor and Methods thereof".  While pretty much all drawer loading optical disc drives are capable of handling both 8cm and 12cm discs, most slot-loading drives will only load standard sized 12cm discs.  So what Apple is trying to patent here is a compactable adapter to allow smaller-sized discs to be loaded in slot-loading drives that only accept standard size discs, such as enabling an 8cm disc to be loaded in a Mac Mini.

While manufacturers can supply an 8cm to 12cm rigid adapter with their 8cm discs to cater for those with slot-loading drives, this would totally defeat the advantage of using 8cm discs in the first place!  A compactable adapter on the other hand could be broken down into several pieces to allow packaging to take advantage of the 8cm disc's smaller size, while still catering for customers who have a slot-loading drive.  This patent includes several embodiments to cover a range of compactable adapter types.

It would be interesting to see if such a compactable adapter would catch on, since if supplying the adapter with 8cm turns out more costly than shipping a 12cm disc on its own or with a product, the product maker would most likely stick with traditional sized 12cm discs to cater for slot-loading drives.

Further in-detail information on this can be read in this Machintosh News Network article.