Nonvolatile families – which device is user-programmable but cannot be erased and reprogrammed afterward?
Correct Answer: PROM
Introduction / Context: Read-only memory technologies vary in how and when data is written. Recognizing which device is one-time programmable is important for cost, security, and field-update decisions. PROMs are intended for a single programming event after fabrication and then behave as fixed ROMs.
Given Data / Assumptions:
- User needs to write content once post-manufacture.
- No erasure mechanism exists in the target technology.
- Functionally read-only after programming.
Concept / Approach: PROM (Programmable ROM) uses fuses/antifuses to permanently set bits. Once programmed, the physical change cannot be undone electrically or optically. By contrast, EPROMs can be UV-erased; EEPROMs and Flash are electrically erasable and reprogrammable. Mask ROMs are factory-set and not user-programmable at all.
Step-by-Step Solution:
1) Exclude mask ROM (not user-programmable).2) Exclude EPROM/EEPROM/Flash (all erasable by UV or electrically).3) Identify PROM as user-programmable, one-time device.4) Conclude PROM matches the description.Verification / Alternative check: PROM datasheets describe “OTP” operation and lack any erase instructions, unlike EPROM/EEPROM/Flash parts.
Why Other Options Are Wrong: Mask ROM is not programmable by the user; EPROM/EEPROM/Flash are erasable and rewritable.
Common Pitfalls: Confusing PROM with EPROM due to similar names; the key difference is erasability.
Final Answer: PROM