CD-ROM physical encoding — naming the recessed features On a pressed CD-ROM, the recessed areas that represent a logical 0 are called what?

Introduction / Context:
Optical discs like CD-ROM store data as microscopic features molded into the polycarbonate substrate. Understanding the terminology for these features helps explain how drives read data using changes in reflectivity.

Given Data / Assumptions:

• Two key surface states exist: pits (recessed) and lands (flat).
• The optical pickup detects reflectivity and phase changes between pits and lands.
• Logical encoding uses transitions; however, many explanations informally associate pits with zeros and lands with ones in didactic contexts.

Concept / Approach:
Pits are tiny depressions formed during pressing; lands are the untouched flat areas. The interference of reflected laser light differs between the two, producing the contrast needed for the photodetector to recover the bitstream after decoding and clock extraction.

Step-by-Step Solution:
Identify recessed features: pits.Identify nonrecessed/flat features: lands.Match the question's “recessed areas” to pits.Therefore, select “Pits”.

Verification / Alternative check:
CD standards (Red Book) and technical diagrams label the depressions as pits and the flat regions as lands; photography of disc surfaces under microscopes confirms the naming convention.

Why Other Options Are Wrong:

• Mounds/Holes: Not standard terms for CD features.
• Lands: Refer to the flat, nonrecessed areas.

Common Pitfalls:

• Over-interpreting logical assignments; the drive actually detects transitions rather than static pit/land levels alone.
• Confusing CD-R dye spots with pressed pits; the reading principle is still reflectivity contrast.

Final Answer:
Pits