Optical storage: pits and lands

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Quick Questions

Shade in the A or B circle for each question.

1. How is data stored on an optical disc?

A As pits and lands along a track

B As tiny magnetised areas on a platter

2. Which describes a pit on an optical disc?

A A flat area of the disc surface

B A tiny dent in the disc surface

3. What happens when the laser shines on a land?

A The light is reflected back to the sensor

B The light is scattered away from the sensor

4. What happens when the laser shines on a pit?

A The light is scattered, so little returns to the sensor

B All of the light is reflected back to the sensor

5. What is the layout of the track on an optical disc?

A Many separate circular tracks that never join

B One long spiral track while the disc spins

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1pit		AA flat area between pits on an optical disc that reflects the laser light straight back to the sensor
2land		BPits and lands are mixed up. A pit is a dent that scatters the light, while a land is the flat area that reflects it back.
3Data on an optical disc is stored along one long spiral track that starts near the centre and winds outwards while the disc spins		Cspiral track
4A laser shines on the spinning disc, and a sensor detects whether the light is reflected back or scattered, which gives the binary data		DA tiny dent in the surface of an optical disc that scatters the laser light instead of reflecting it straight back
5A pit is a flat area that reflects the laser back to the sensor		Elaser reflection
6An optical disc stores data in magnets that are read by a laser		FOptical discs do not use magnetism. They store data as pits and lands, and the laser reads how light reflects off them.

Definitions

pits and lands

Fill in the Blanks

Complete each line of code by filling in the missing parts.

IF surface = PIT THEN light ← _________ ENDIF

IF surface = ____ THEN light ← REFLECTED ENDIF

discSpinning ← TRUE trackShape ← ______

writing ← TRUE IF writing THEN laser.create(____)

changes ← DETECT(laser, disc) data ← CONVERT(changes, ______)

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A disc spins in the drive

B laser shines on the track

C light hits a flat land

D light scatters away

Question 2

A laser reads the spiral track

B a land is a flat area

C a pit reflects all the light

D sensor sees less light

Question 3

A WRITE data to optical disc

B laser aims at spiral track

C laser burns pits where needed

D untouched areas become pits

Question 4

A pits are flat areas on a disc

B lands are flat areas

C laser reads reflected light

Question 5

A disc spins in the drive

B laser moves along the track

C track is concentric rings

D it runs from centre to edge

Answer Key

Optical storage: pits and lands

Section A: Quick Questions

A — As pits and lands along a track

B — A tiny dent in the disc surface

A — The light is reflected back to the sensor

A — The light is scattered, so little returns to the sensor

B — One long spiral track while the disc spins

Section B: Match the Pairs

pit → A tiny dent in the surface of an optical disc that scatters the laser light instead of reflecting it straight back

land → A flat area between pits on an optical disc that reflects the laser light straight back to the sensor

Data on an optical disc is stored along one long spiral track that starts near the centre and winds outwards while the disc spins → spiral track

A laser shines on the spinning disc, and a sensor detects whether the light is reflected back or scattered, which gives the binary data → laser reflection

A pit is a flat area that reflects the laser back to the sensor → Pits and lands are mixed up. A pit is a dent that scatters the light, while a land is the flat area that reflects it back.

An optical disc stores data in magnets that are read by a laser → Optical discs do not use magnetism. They store data as pits and lands, and the laser reads how light reflects off them.

Section C: Definitions

pits and lands — Dents (pits) and flat areas (lands) along a disc's spiral track. A laser reads them by how light reflects: lands reflect it back, pits scatter it. The changes store binary data.

Section D: Fill in the Blanks

IF surface = PIT THEN
    light ← SCATTERED
ENDIF

IF surface = LAND THEN
    light ← REFLECTED
ENDIF

discSpinning ← TRUE
trackShape ← SPIRAL

writing ← TRUE
IF writing THEN laser.create(PITS)

changes ← DETECT(laser, disc)
data ← CONVERT(changes, BINARY)

Section E: Spot the Error

D — A land is a flat area, so it reflects the laser light straight back to the sensor. Pits are the parts that scatter light. The line should be: light reflects back to sensor.

C — A pit is a dent, so it scatters the laser light instead of reflecting it back. Only lands reflect the light cleanly. The line should be: a pit scatters the light.

D — When writing, the laser makes the pits. Areas it does not touch stay flat, so they remain lands. The line should be: untouched areas stay as lands.

A — Pits are dents in the disc surface. Lands are the flat areas. The line should be: pits are dents in the disc.

C — An optical disc has one continuous spiral track, not separate concentric rings. The line should be: track is one long spiral.