Hard disk drives have a microprocessor, with internal “software” that runs them and make the drive work. The firmware instructions are embedded into read-only memory, this code is similar with the system BIOS.

The firmware is not fully resident in PCB, some parts are in sectors forming the so called Service Area (SA).

The firmware stored in SA is modular and we can find 3 kind of modules:

Data Modules – managing data area (eg. P-list and G-List)
Management Modules – managing the hdd basic functionality
Techno Modules – managing SA access operations

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