A new optical disc format known as the Blu- ray Disc (BD) is becoming popular. In what way is it different from the traditional DVD?
- 1.DVD supports Standard Definition video while BD supports High Definition Video.
- 2.Compared to a DVD, the BD format has several times more storage capacity.
- 3.The thickness of BD is 2.4 mm while that of DVD is 1.2 mm.
Which of the statements given above is/are correct?
Answer & explanation
Answer: (b) 1 and 2 only
Blu-ray uses a shorter-wavelength blue-violet laser, so it packs data far more densely. That gives it several times the capacity of a DVD and lets it carry high-definition video. The disc is not 2.4 mm thick. Like a DVD, a Blu-ray disc is 1.2 mm thick and 120 mm across; what differs is its much thinner 0.1 mm cover layer.
- ✓ 1. DVD is the standard-definition video format, and Blu-ray was built to carry high-definition video. Its much larger storage capacity is what makes full HD films practical on a single disc.
- ✓ 2. A single-layer Blu-ray disc holds 25 GB and a dual-layer disc 50 GB. A single-layer DVD holds only 4.7 GB, so Blu-ray offers roughly five times the capacity or more.
- ✗ 3. The 1.2 mm figure for DVD is right; the ECMA-267 DVD standard gives 1.20 mm. A Blu-ray disc is also 1.2 mm thick, not 2.4 mm. The thickness difference lies in the protective cover layer over the data: 0.1 mm for Blu-ray against 0.6 mm for DVD.
Remember · Blu-ray: blue-violet 405 nm laser, 25 GB per layer (DVD 4.7 GB), HD video. Both discs are 120 mm across and 1.2 mm thick. In thickness, only the cover layer differs (0.1 mm against 0.6 mm).
Sources
- Encyclopaedia Britannica – Blu-ray ↗ · reference work “A single-layer Blu-ray disc can hold 25 gigabytes, whereas a single-layer DVD holds only 4.7 GB.”
- ECMA-267, 120 mm DVD Read-Only Disk (3rd edition, April 2001) ↗ · reference work “The thickness of the disk, including adhesive layer, spacer(s) and label(s), shall be + 0,30 mm e1 = 1,20 mm - 0,06 mm”
- Hwu, Hacking CD/DVD/Blu-ray for Biosensing, ACS Sensors 2018 (NIH PMC) ↗ “cover layer 16 (CD: 1.1 mm, DVD: 0.6 mm, Blu-ray: 0.1 mm in thickness) protects the data pits from being destroyed by scratching”
Question: UPSC Civil Services (Preliminary) 2011, General Studies Paper I. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). ·
