Previous Year Question
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?
DVD supports Standard Definition video while BD supports High Definition video.
Compared to a DVD, the BD format has several times more storage capacity.
Thickness of BD is 2.4 mm while that of DVD is 1.2 mm.
Which of the statements given above is/are correct?
Only 1
1 and 2
2 and 3
1, 2 and 3
Correct Answer: B
Detailed Solution
Statement 1 is correct. DVD was primarily developed for the storage and playback of Standard Definition video, whereas the greater storage capacity of a Blu-ray Disc made it possible to store High Definition video and high-quality audio.
The usual resolution of DVD video is approximately 720 × 576 pixels in the PAL system and about 720 × 480 pixels in the NTSC system. The Blu-ray format can support High Definition resolutions such as 1280 × 720 and 1920 × 1080. Ultra HD Blu-ray was subsequently developed for a resolution of 3840 × 2160.
Statement 2 is correct. A standard single-layer DVD has a storage capacity of approximately 4.7 GB, while a dual-layer DVD has a capacity of about 8.5 GB. In contrast, a single-layer Blu-ray Disc can store approximately 25 GB, while a dual-layer disc can store about 50 GB of data.
Blu-ray uses a blue-violet laser with a wavelength of approximately 405 nanometres, whereas a DVD uses a red laser with a wavelength of about 650 nanometres. The shorter wavelength of Blu-ray enables data to be read and written in smaller pits with reduced track spacing. Therefore, more data can be stored on a disc of the same size.
Statement 3 is incorrect. Both a Blu-ray Disc and a DVD normally have a diameter of 120 mm and a total thickness of approximately 1.2 mm. Therefore, stating that a Blu-ray Disc is 2.4 mm thick is incorrect. The position of the data layers and the structure of the protective layers may differ between the two formats, but their total standard thickness is the same.