"Discs
A disc refers to optical media, such as an audio CD, CD-ROM, DVD-ROM, DVD-RAM, or DVD-Video disc. Some discs are read-only (ROM), others allow you to burn content (write files) to the disc once (such as a CD-R or DVD-R, unless you do a multisession burn), and some can be erased and rewritten over many times (such as CD-RW, DVD-RW, and DVD-RAM discs).
All discs are removable, meaning when you unmount or eject the disc from your desktop or Finder, it physically comes out of your computer.
Disks
A disk refers to magnetic media, such as a floppy disk, the disk in your computer's hard drive, an external hard drive. Disks are always rewritable unless intentionally locked or write-protected. You can easily partition a disk into several smaller volumes, too.
Disks are usually sealed inside a metal or plastic casing (often, a disk and its enclosing mechanism are collectively known as a "hard drive")." http://support.apple.com/kb/ht2300
Sorry again for adding to the list, but you're the only one left with this. Please reupload when you have the time, thanks. みずカノ
Also, could you update this to Ver1.31? It wasn't listed, but it definitely got updated. 隷属と解放のラビリンス