Mask ROM limitations in system design What is a major disadvantage of mask ROM when system requirements or stored data must change after manufacture?

Introduction / Context:
Mask ROM (Read-Only Memory) is programmed during semiconductor fabrication by customizing photolithographic masks. It is excellent for high-volume, fixed-content applications but poses challenges when data or firmware needs to be updated after production.

Given Data / Assumptions:

• Mask ROM content is physically set by the manufacturer before packaging.
• After fabrication, the stored data cannot be changed in the field.
• Updates would require an entirely new mask set and re-fabrication run.

Concept / Approach:

Because the bit pattern is “hardwired,” mask ROM devices are non-reprogrammable. Any change implies creating new masks (with significant non-recurring engineering cost) and re-manufacturing, which is impractical for small changes or low volumes.

Step-by-Step Solution:

Verification / Alternative check:

Compare with EPROM/EEPROM/Flash that allow erasure and reprogramming. Mask ROM lacks this ability entirely.

Why Other Options Are Wrong:

• Time consuming or very expensive may be true indirectly, but the absolute limitation is non-reprogrammability.
• Short life expectancy is incorrect; ROM content is stable and long-lived.

Common Pitfalls:

• Confusing mask ROM with OTP EPROM (one-time programmable) which can be programmed once by the user.

Final Answer:

cannot be reprogrammed if stored data needs to be changed