Magnetic disks — track organization: On a rotating magnetic disk, each concentric track is subdivided into which smaller addressable units?

Introduction / Context:
Understanding how magnetic disks organize data physically is essential for topics such as file systems, disk scheduling, and performance tuning. Tracks, sectors, and blocks are foundational terms that map the physical medium to logical storage.

Given Data / Assumptions:

• A disk surface contains concentric circular tracks.
• Each track is further divided for addressable data storage.
• Modern disks may also use zone bit recording, but the basic addressable unit remains consistent.

Concept / Approach:

The smallest addressable physical unit on a track is a sector. Traditionally, sectors store a fixed number of bytes (commonly 512 bytes or 4096 bytes in advanced format drives). File systems build larger logical blocks on top of physical sectors for efficiency and alignment.

Step-by-Step Solution:

Verification / Alternative check:

Disk specifications and low-level formatting utilities reference CHS (cylinders, heads, sectors), confirming sectors are the canonical subdivision of tracks.

Why Other Options Are Wrong:

• Periods / groups: Not standard magnetic disk terms for track subdivision.
• Zones: In zone bit recording, a zone is a collection of tracks with the same sectors-per-track, not the basic subdivision of a single track.
• None of the above: Incorrect because sectors is correct.

Common Pitfalls:

Confusing logical blocks with physical sectors; assuming all tracks have the same number of sectors (not necessarily true in zoned recording).

Final Answer:

sectors