In computers, a DVD-ROM is:

Concept

Storage media are classified two ways. By the recording/read technology, a medium is either optical (data read and written with a laser beam, e.g. CD, DVD, Blu-ray) or magnetic (data stored as magnetised regions, e.g. hard disk, floppy, magnetic tape). By write capability, the suffix tells the story: ROM means Read-Only Memory — the data is mastered (stamped) once at manufacture and cannot be rewritten by the user.

Applying it to DVD-ROM

• "DVD" is a Digital Versatile Disc — its tracks are read by a laser, so the medium is optical, not magnetic.

• The "ROM" suffix means the disc is pressed once at the factory and is read-only thereafter — in the language of these options, it can be "written only once" and never re-written by the user.

Combining both facts: a DVD-ROM is an optical storage medium that can be written only once.

Contrast with the other choices

• Optical + written many times: describes a re-writable optical disc such as DVD-RW/DVD-RAM, not a ROM disc.

• Magnetic + written only once: wrong on both counts — a DVD is optical, and write-once is a property of ROM optical discs, not of magnetic media.

• Magnetic + written many times: fits a hard disk or floppy (magnetic, rewritable), but a DVD is not magnetic.