Programmable ROM types: Select the best description of a fusible-link PROM device and its programmability.

Introduction / Context:
Fusible-link PROMs were among the earliest field-programmable nonvolatile memories. Knowing their programming model and limitations helps distinguish them from EPROM, EEPROM, and Flash devices used today.

Given Data / Assumptions:

• PROM is shipped blank and later programmed by the user.
• Programming irreversibly blows selected fuses to encode bits.
• No erase capability exists once programmed.

Concept / Approach:
In a fusible-link PROM, each bit is formed by a tiny link (fuse). Applying a programming current opens the link to change the stored bit. Because this is a physical, destructive change, the device is one-time programmable (OTP). Although some PROMs are programmed by manufacturers (mask ROM), the “fusible-link PROM” specifically refers to a user-programmable OTP technology.

Step-by-Step Solution:

Verification / Alternative check:
Historical datasheets list programming currents and verify that programmed bits cannot be restored, confirming OTP behavior.

Why Other Options Are Wrong:

• Manufacturer programmable, OTP: Describes mask ROM, not fusible-link PROM.
• User programmable, reprogrammable: Describes EEPROM/Flash or UV-erasable EPROM, not fusible-link PROM.
• Manufacturer programmable, reprogrammable: Not applicable to PROMs.

Common Pitfalls:
Confusing mask ROM with PROM, or assuming any PROM can be erased; fusible-link PROM cannot be returned to a blank state.

Final Answer:
user programmable, one-time programmable