Read-only memory (ROM): Select the most accurate description of ROM usage and data retention in digital systems.

Introduction / Context:
ROM is the canonical storage for fixed firmware, bootloaders, lookup tables, and calibration constants that must persist across power cycles. Clarifying ROM's volatility and use-case helps distinguish it from RAM in architectures and memory maps.

Given Data / Assumptions:

• ROM refers to data that is not routinely altered during normal operation.
• ROM is nonvolatile—contents persist without power.
• Implementation may be mask ROM, OTP, EEPROM/Flash treated as ROM by software.

Concept / Approach:
ROM stores instructions/configuration that remain constant during use. While some systems can field-update flash “ROM,” the operational model is that the code is read, not written, during normal operation, and it is retained after power removal. Therefore, “nonvolatile” and “does not change during operation” best describe ROM.

Step-by-Step Solution:

Verification / Alternative check:
Boot sequences read from ROM even after prolonged power-off; RAM must be initialized anew at each boot.

Why Other Options Are Wrong:

• Nonvolatile but changes during operation: That is more like EEPROM/Flash used as NVM data store, not ROM behavior.
• Volatile options: Contradict persistence requirement of ROM.

Common Pitfalls:
Equating “Flash” with “always writable”; in many systems it is logically treated as ROM, updated only under special procedures.

Final Answer:
nonvolatile, used to store information that does not change during system operation