Discussion
Which of these is an example of an optical storage device?
Answer: B
Correct answer: DVD
A DVD is optical storage: data is written as microscopic pits on a reflective layer and read by a laser detecting the change in reflection. CDs and Blu-ray discs work the same way. The three storage technologies are distinguished by how the data is held. Magnetic storage - hard disks, tape - uses the orientation of magnetic domains. Optical storage uses pits read by a laser. Solid-state storage - SSDs, USB flash drives, memory cards - traps charge in floating-gate transistors with no moving parts at all. Optical media have particular strengths: they are cheap to mass-produce by stamping, immune to magnetic fields, and reasonably durable. Their weaknesses are low capacity, slow access and the need for a drive, which is why they have largely disappeared from laptops. RAM is not storage in this sense at all but volatile working memory.
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