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PROM vs. EPROM: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on February 16, 2024
PROM (Programmable Read-Only Memory) is a type of read-only memory that is programmed after manufacturing; EPROM (Erasable Programmable Read-Only Memory) is PROM that can be erased and reprogrammed.

Key Differences

PROM, or Programmable Read-Only Memory, is a form of digital memory where the data is written permanently and cannot be altered or erased. EPROM, which stands for Erasable Programmable Read-Only Memory, is a type of PROM that allows the data to be erased, typically using ultraviolet light, and reprogrammed.
In PROM, once data is written, it is fixed and cannot be changed, making it ideal for storing firmware or permanent software instructions. EPROM, however, can be erased and reused, offering flexibility for updating or modifying the stored data.
The process of programming a PROM involves burning fuses within the chip, which is irreversible. On the other hand, programming an EPROM involves charging the floating gates in the memory cells, which can be reset through exposure to strong ultraviolet light.
PROM is typically used in applications where the data needs to remain constant and secure, such as in embedded systems. EPROM finds its use in environments where the need for updating the stored information might arise, such as in development systems or early-stage prototypes.
The key distinction lies in their reusability; PROM is a write-once, read-many-times type of memory, while EPROM offers the convenience of being erased and reprogrammed multiple times, making it more adaptable to changes.

Comparison Chart


Programmable once; permanent data storage
Re-programmable; data can be erased and rewritten


Erasable with UV light or electrically

Use Case

Ideal for permanent data storage
Suitable for experimental or evolving projects

Data Stability

Highly stable; no risk of accidental erasure
Data can be intentionally altered

Manufacturing Process

Fuses are burnt to store data
Data stored using floating-gate transistors

PROM and EPROM Definitions


Non-volatile storage used in computers and other devices.
The PROM in this machine contains the basic instructions for starting up.


A reprogrammable memory chip that can be erased using ultraviolet light.
The EPROM was erased and reprogrammed with the updated firmware.


A memory chip storing data permanently.
The device's firmware is stored on the PROM, ensuring it can't be easily altered.


A type of non-volatile memory used in computers and electronics.
The technician used an EPROM to test different versions of the software.


Permanent storage solution for digital devices.
The game's code was burned onto a PROM chip.


A flexible storage solution for electronic devices.
The EPROM's versatility made it perfect for the prototype's memory needs.


A type of read-only memory that is programmed after manufacturing.
They used a PROM to store the software as it doesn’t need regular updates.


Erasable and programmable memory for storing code and data.
They chose an EPROM for easy updates to the control system.


A semiconductor device used for storing data.
The company used a PROM for reliable long-term data storage.


A memory device that allows data correction and updating.
After finding a bug, the developers erased the EPROM to upload the fix.


A kind of read-only memory whose contents can be set after manufacture, but only once.


A programmable ROM that can be erased by exposure to ultraviolet light and then reprogrammed.


A formal dance held for a high-school or college class typically at or near the end of the academic year.


(computer science) a read-only memory chip that can be erased by ultraviolet light and programmed again with new data


(British) A promenade concert.


A promenade.


(US) A formal ball held at a high school or college on special occasions; e.g,. near the end of the academic year.
Would you like to be my prom date?


A formal ball held for a school class toward the end of the academic year


What is PROM?

PROM is a type of read-only memory that is programmed once after manufacturing.

How is data erased from an EPROM?

Data is erased from an EPROM by exposing it to strong ultraviolet light.

What is EPROM?

EPROM is a type of PROM that can be erased with ultraviolet light and reprogrammed.

Are PROM and EPROM still used today?

Yes, though less common, they are still used in certain applications requiring stable, long-term data storage.

Can data in a PROM be modified?

No, once data is programmed into a PROM, it cannot be modified or erased.

Is EPROM more versatile than PROM?

Yes, because EPROM can be erased and reprogrammed, it's more versatile than PROM.

What happens if you try to rewrite a PROM?

PROM cannot be rewritten; any attempt to do so would be ineffective.

What are common uses for PROM?

PROM is commonly used for storing firmware or permanent software in embedded systems.

Is a special device required to program PROM?

Yes, a PROM programmer is required to encode data onto a PROM chip.

What are common uses for EPROM?

EPROM is used in situations where data might need to be updated, like in development systems.

Can PROM be used in consumer electronics?

Yes, PROM can be used in consumer electronics for permanent code storage.

What's a key advantage of PROM over EPROM?

PROM's key advantage is its permanent storage, ensuring data integrity over time.

Can EPROM be used for temporary data storage?

Yes, EPROM can be used for temporary storage since it can be rewritten.

What is the main limitation of PROM?

The main limitation of PROM is its one-time programmability.

Are PROM and EPROM susceptible to data loss over time?

Both PROM and EPROM are quite stable and not prone to data loss over time.

How long does it take to erase an EPROM?

Erasing an EPROM with UV light typically takes 5 to 20 minutes, depending on the intensity of the light.

How many times can an EPROM be reprogrammed?

An EPROM can typically be reprogrammed thousands of times before it wears out.

Can EPROM be erased electrically?

Some EPROM variants can be erased electrically, known as EEPROM.

Is ultraviolet light always needed to erase EPROM?

Traditional EPROM requires ultraviolet light, but EEPROM variants can be erased electrically.

Is EPROM more expensive than PROM?

Generally, EPROM can be more expensive than PROM due to its reusability and technology involved.
About Author
Written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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