Briefly discuss the structure of the hard disk with a block diagram.

A hard disk drive (HDD) is a non-volatile secondary storage device that stores data magnetically on rotating platters.

Structure (block diagram):

Platters → Heads → Spindle → Actuator Arm → Controller Board → Interface (SATA)

Components:

1. Platters — Aluminium/glass disks coated with magnetic material. Both sides store data in tracks and sectors. Example: 1 TB disk has 2–3 platters.
2. Read/Write Heads — One per surface, floats nanometres above platter to read/write without touching.
3. Spindle Motor — Spins platters at 5400/7200 RPM for fast access.
4. Actuator Arm — Moves heads to the correct track, like a record-player arm.
5. Controller + Cache — Circuit board with small buffer (64 MB) managing commands via SATA interface.

Data is addressed as Cylinder-Head-Sector. Though SSDs are replacing HDDs, HDDs remain common for bulk backup in Nepal offices due to low cost per GB.