Know and understand optical drives including CD, DVD, Blu-ray

Topic: 3 Storage Devices and Media

Objective

Know and understand optical drives including CD, DVD, Blu‑ray.

What is an Optical Drive?

An optical drive reads and writes data using a laser beam. Think of it like a laser pointer that can read the tiny bumps on a disc’s surface, turning them into digital information. The laser’s wavelength determines how small the bumps can be, which in turn affects how much data can fit on the disc.

Compact Disc (CD)

A CD is the original optical format, introduced in the early 1980s. It uses a laser with a wavelength of 780 nm, which limits the data density.

• Capacity: ≈ 700 MB ($1 \text{ CD} \approx 700 \text{ MB}$)
• Typical uses: music, software, small data backups
• Laser type: infrared
• Speed: 1× = 150 kB/s, 2× = 300 kB/s

Digital Versatile Disc (DVD)

DVDs use a shorter‑wavelength laser (650 nm), allowing more data to be stored in the same disc area.

• Capacity: 4.7 GB (single‑layer), 8.5 GB (dual‑layer)
• Typical uses: movies, large software, high‑quality audio
• Laser type: red
• Speed: 1× = 1.32 MB/s, 2× = 2.64 MB/s

Blu‑ray Disc (BD)

Blu‑ray uses an even shorter laser (405 nm), which means the bumps on the disc can be much smaller, so more data fits on the same surface.

• Capacity: 25 GB (single‑layer), 50 GB (dual‑layer)
• Typical uses: 4K video, high‑definition audio, large game installs
• Laser type: blue‑violet
• Speed: 1× = 4.5 MB/s, 2× = 9 MB/s

Comparison Table

Key Terms

• Optical Drive – a device that reads/writes data using a laser.
• Laser Wavelength – determines the size of the data pits; shorter wavelengths = higher density.
• Read/Write Head – the part that moves across the disc surface.
• Capacity – how much data a disc can hold.
• Speed (×) – how fast data is read/written; 1× = base speed.

Quick Quiz

1. Which optical format uses a blue‑violet laser? Answer: Blu‑ray.
2. What is the approximate capacity of a single‑layer DVD? Answer: 4.7 GB.
3. Why do shorter laser wavelengths allow more data on a disc? Answer: They can read smaller pits, increasing data density.