PROM vs EPROM vs EEPROM: What’s the Difference?

When you pick the right kind of read-only memory, you must know the main differences between PROM, EPROM, and EEPROM. Each rom type keeps data in its own way. PROM vs EPROM affects how you change or remove data in your device. For example, EEPROM is used the most in embedded systems today, as shown below:

Memory Type	Market Share (%)
EEPROM	45
PROM	N/A
EPROM	N/A

You can see that rom types are not the same in how you set, erase, or use them again. Choosing the best read-only memory for your project helps make sure it works well and lasts long.

Key Takeaways

• PROM is a type of memory you can program only once. After you write data, you cannot change it. PROM is good for data that will never change.

• EPROM can be erased and programmed again with ultraviolet light. This is helpful if you need to update data sometimes.

• EEPROM lets you erase and write new data without taking out the chip. It works well for things that need many updates, like microcontrollers.

• When picking memory, think about how often you will change data. PROM is best if you never need to change it. EPROM is good for rare changes. EEPROM is best for lots of changes.

PROM Overview

What is PROM

You might hear about programmable read-only memory in digital devices. PROM means programmable read-only memory. You use PROM to save data that stays the same after writing. You can only write to PROM one time. After you put in the data, you cannot change or erase it. PROM is non-volatile memory, so it keeps your data even when the power is off.

How PROM Works

PROM has tiny fuses inside its chip. When you program PROM, you burn these fuses. This makes a pattern of ones and zeros. The pattern holds your data. You cannot fix the fuses, so you cannot change the data. This is not like eprom or erasable programmable read only memory, which let you erase and reuse the chip. PROM is easy to use and good for saving fixed information.

PROM Programming

You need a special device called a programmer to set up PROM. The programmer sends electricity to the chip. This burns the fuses to match your data. Here is how PROM programming is different from other memory types:

• PROM uses a programmer and electricity to write data. It is a one-time programmable device.

• EPROM can be erased and programmed again with ultraviolet light. You can use it many times.

• EEPROM lets you erase and rewrite single bytes with electricity. It is more flexible than PROM and EPROM.

You cannot erase or change PROM after you program it. This is why PROM is used when you want your data to stay the same forever.

PROM Characteristics

PROM chips come in many sizes and types. Here is an example from a datasheet:

Part Number	Description	Capacity
74S287	256 x 4 (1024-BIT TTL PROM)	1024 bits

You can find programmable read-only memory in lots of devices. PROM is used in home appliances, cars, and machines. Here are some common uses:

Use Case	Description
Home Appliances	Washing machines and microwaves use PROM for control programs that do not change.
Automotive Systems	PROM stores ECU software and important functions that must stay the same.
Industrial Automation	It keeps machine instructions for steady performance.
Consumer Electronics	PROM saves user settings and factory-default setups in devices.
Digital Signal Processing Devices	It holds lookup tables and values needed for real-time processing.

PROM keeps your data safe for a long time. Studies show PROM works well for at least six months after you program it. PROM is very reliable when you need to save data that never changes. You should pick PROM if you want simple, permanent storage and do not need to erase or update your data like you can with eprom.

EPROM Overview

What is EPROM

EPROM is called erasable programmable read-only memory. This chip stores data even when the power is off. You can erase and rewrite EPROM many times. It is used in computers and cars that need updates. EPROM has a special window for ultraviolet light to erase data.

Note: EPROM is more flexible than PROM. You can erase and rewrite EPROM. This helps you fix bugs or update software.

How EPROM Works

EPROM chips have a grid of transistors. Each transistor holds a 1 or 0 by trapping electrons. To erase EPROM, shine ultraviolet light through the quartz window. The light clears the electrons and sets all bits to 1. You can then put in new data. EPROM keeps data safe for up to twenty years if you cover the window.

Here is a table with EPROM’s main features:

Feature	Description
Non-volatile	Keeps data without power
Erasable	You can erase and rewrite using UV light
Programming Method	Needs a PROM burner and high-voltage pulses
Data Retention	Holds data for up to 20 years
Read Cycles	Supports many reads if the window stays covered
Design Features	Has a quartz window for UV light, covered after programming

EPROM Programming

You need a special device to program EPROM. This device sends high-voltage pulses to the chip. Here are the steps to program EPROM:

1. Erase all bits to set them to 1.

2. Use the programming voltage.

3. Raise the supply voltage if needed.

4. Put your data in a buffer.

5. Set the address and data for each spot.

6. Use a pulse to write each byte.

7. Check each byte to make sure it matches.

You can erase and rewrite EPROM many times. You must use the right tools. This is different from eeprom, which erases and rewrites single bytes with electricity.

EPROM Erasing

To erase EPROM, shine ultraviolet light through the quartz window. Sunlight can also erase EPROM, but it is not reliable. Always cover the window after programming to protect your data. Do not put EPROM on insulating surfaces. This can cause static damage. Use conductive materials to keep the chip safe.

• EPROM lets you erase and rewrite data with UV light.

• eeprom erases and rewrites data with electricity, so it is easier to update.

Tip: Label the window after programming. This keeps your data safe from light.

EPROM is used in many devices. You find it in computer BIOS, embedded systems, electronics, cars, and machines. EPROM helps you test and update code when making products. It is a good choice for prototyping.

EEPROM Features

What is EEPROM

EEPROM is used in many new electronic devices. EEPROM means electrically erasable programmable read-only memory. This chip lets you save important data. You can change the data later if you need to. EEPROM is non-volatile memory, so it keeps data when power is off. You can update EEPROM anytime you want. Many people pick EEPROM because you can use it again and again. It works well for storing small amounts of data.

Tip: You see EEPROM in microcontrollers, embedded systems, and memory cards. It saves settings, calibration data, and firmware updates.

How EEPROM Works

EEPROM has a special way to store and change data. Each cell holds one bit of information. You can erase or write each byte by itself. This makes EEPROM very flexible. You do not need to take out the chip or turn off your device to update data. The chip uses tunneling to move electrons and change the value.

Here is a table with common technical features of EEPROM:

Feature	Description
Performance Measures	Data rate, access time, data retention, endurance, logic family
Power Usage	Supply voltage, power dissipation, operating current, standby current
Important Specifications	Density, number of words, bits per word, bus type, production status

EEPROM Programming

You can program EEPROM while it stays in your device. This is called in-circuit programming. EEPROM uses tunneling to write data. You do not need to erase the whole chip first. You can change just one byte at a time. This is not like EPROM or PROM.

Memory Type	Programming Method	Erasing Method	Operational Requirement
EPROM	Hot electron injection	Remove from circuit	Must erase before reprogramming
EEPROM	Tunneling effect	In-circuit, no power off	Can be reprogrammed in-circuit

• EPROM uses hot electron injection and must be taken out to erase.

• EEPROM uses tunneling and lets you erase and reprogram data without turning off the device.

EEPROM Erasing

You can erase EEPROM fast and easily. The chip lets you erase and reprogram data without turning off your device. You can erase one byte at a time. This gives you lots of flexibility for updates. Erasing one byte in EEPROM takes about 5 milliseconds. This is much faster than block-level memory like SPI flash. EEPROM can be written and erased thousands of times. This makes it great for saving settings or calibration data that change often.

• EEPROM lets you erase and write one byte at a time.

• You get high endurance and reliable performance for small updates.

• EEPROM keeps data when power is off, so your information stays safe even if you unplug your device.

PROM vs EPROM

Programming Comparison

PROM and EPROM are different in how you put in data. You can only program PROM one time. After you write data, you cannot change it. This makes PROM good for saving things that never change. EPROM is not like PROM. You can erase and reprogram EPROM if you need to fix mistakes or update data. The table below shows how they are not the same:

Feature	PROM	EPROM
Reusability	Not reusable	Reusable multiple times
Writing Process	Irreversible	Reversible
Error Handling	Becomes unusable	Can be reused after error
Flexibility	Better for fixed data	More flexible for updates

PROM is best if you want storage that never changes. EPROM is better if you need to update your data.

Erasing Comparison

Erasing data is another big difference between PROM and EPROM. You cannot erase PROM at all. Once you put in data, it stays forever. EPROM is different because you can erase it. You shine ultraviolet light through a window on the chip. This clears all the data so you can write new information. But you must take EPROM out of your device to do this. This makes EPROM harder to use if you need to update data a lot.

Reusability

Many people pick EPROM because you can use it again. PROM is a one-time memory. You cannot use PROM again after writing data. EPROM can be erased and programmed many times. You just need ultraviolet light to clear the chip. This makes EPROM good for testing or changing code. In summary:

• PROM is not reusable. You can only use it once.

• EPROM is reusable. You can erase and program it again.

When you look at PROM and EPROM, think about how often you need to change your data. If you want a chip you can use more than once, EPROM is the better choice.

EPROM vs EEPROM

Erasing Methods

The biggest difference is how you erase data. EPROM needs ultraviolet light to clear all the data. You have to take out the chip from your device. Then you put it under a UV lamp. This takes a few minutes. It erases the whole chip at once. EEPROM uses electric signals to erase data. You do not need to remove the chip. You do not need any special light. You can erase just one byte or a small part. This makes EEPROM easier for updates.

Memory Type	Erasing Method
EPROM	Erased using UV light (entire chip)
EEPROM	Erased using electric signals (byte-level)

Tip: EEPROM lets you update only a small part. This saves time and gives you more control.

Speed and Flexibility

Speed and flexibility matter when you pick memory. EPROM reads and writes data fast. But erasing takes longer because of the UV light. You must remove the chip every time you want to erase or reprogram it. EEPROM is different. You can erase and write data one byte at a time. You do not need to take out the chip. This makes EEPROM much more flexible. You can update data quickly while the chip stays in your device.

• EPROM needs UV light to erase, so it is slower and less flexible.

• EEPROM uses electric signals, so you can erase and write data instantly.

• Most new BIOS chips use EEPROM because it is fast and easy.

Feature	EPROM	EEPROM
Flexibility	Remove chip for reprogramming	In-circuit erase/write at byte level
Speed	Fast read/write, slow erase	Instant erase/write, longer access for serial types

Application Differences

You use EPROM and EEPROM in different ways. EPROM keeps data safe even when power is off. But you need UV light to erase it. This makes EPROM less common now. You might see EPROM in old devices or places where updates are rare. EEPROM also keeps data safe. But you can erase and write data with electricity. This makes EEPROM popular in embedded systems, microcontrollers, BIOS chips, smart cards, and cars. You can store settings, calibration data, and firmware updates with EEPROM.

Memory Type	Characteristics	Typical Applications
EPROM	Non-volatile, UV light for erasure	Limited use, older systems, rare in new designs
EEPROM	Non-volatile, electrically erasable	Embedded systems, microcontrollers, BIOS, smart cards, cars

Note: EPROM is not used much in new projects. EEPROM fits modern needs better and gives you more choices.

PROM vs EPROM vs EEPROM

Comparison Table

It is important to look at memory types before you pick one. Each type has good points and bad points. The table below shows how prom, eprom, and eeprom are different. You can see the cost, speed, use, and how many times you can program each one.

Feature	PROM	EPROM	EEPROM
Programming	One-time only	Many times (after erasing)	Many times (byte-level)
Erasing Method	Not possible	UV light (entire chip)	Electrical (byte or block)
Reusability	No	Yes	Yes
Typical Speed	Fast read, one-time write	Fast read, slow erase	Moderate read/write, fast erase
Program Cycle Lifetime	1	100–1,000 cycles	1,000,000+ cycles
Data Retention	10+ years	10–20 years	10+ years
In-Circuit Update	No	No	Yes
Cost	Higher than eprom	More economical than prom	Much higher than flash memory

? Tip: eeprom costs a lot more than NOR or NAND flash memory. For 1 byte of eeprom, you pay about 10,000 times more than NOR flash. The price is about 10 million times more than NAND flash. If you want to save money, you should use eprom or prom for simple data that does not change.

Typical Uses

You find prom, eprom, and eeprom in many kinds of devices. Each type is good for a different job. Pick the one that fits what you need.

• PROM

  • Use prom when you want to keep data that never changes.

  • You see prom in simple control systems, home appliances, and some car parts.

  • Makers use prom to set factory settings or calibration data.

  • You cannot update prom after you write data, so it is best for instructions that stay the same.

• EPROM

  • Pick eprom if you need to change data sometimes.

  • You find eprom in old computers, early BIOS chips, and test tools.

  • Engineers use eprom for testing and making new things because they can erase and program it again.

  • You must take eprom out of the circuit to erase it, so it is not as flexible as eeprom.

• EEPROM

  • Use eeprom if you need to change data often and keep it safe when power is off.

  • You see eeprom in microcontrollers, smart cards, and new car electronics.

  • Many embedded systems use eeprom to save settings, passwords, or calibration data.

  • You can update eeprom while it stays in the device, which makes things easier and faster.

? Note: eeprom gives you the most choices. You can erase and write single bytes without taking out the chip. This makes eeprom the best pick for new electronics that need lots of updates.

Think about what your project needs. If you want low cost and data that never changes, prom is a good choice. If you need to update data a few times, eprom works well. If you want quick, easy updates and long life, eeprom is the best pick.

Choosing the Right Memory

Application Needs

Think about your project before picking a memory type. PROM is good if you want data that never changes. You see PROM in things like washing machines and control panels. EPROM is better if you need to update data sometimes. EPROM is found in old computers and test tools. EEPROM is best if you change data a lot. You find EEPROM in microcontrollers, smart cards, and car electronics.

? Tip: Write down what your device needs. Ask if you will update data or keep it the same. This helps you pick the right memory.

Pros and Cons

Every memory type has good and bad sides. You should check these before you choose. The table below shows the main pros and cons:

Memory Type	Pros	Cons
PROM	Simple and cheap for one-time programming	Can only be programmed once, no erasing
EPROM	Can be erased and programmed again, keeps data for 10-20 years	Needs UV light to erase, needs a programmer
EEPROM	Can be erased and programmed with electricity, keeps data after power loss	Slower than other types, fewer write cycles than RAM

PROM gives you easy and cheap storage. EPROM lets you fix mistakes and update data, but you need special tools. EEPROM makes updates easy and keeps data safe, but it is slower and wears out after many writes.

Real-World Examples

You see these memory types in lots of devices. PROM stores codes in home appliances. EPROM helps engineers test new software in old computers. EEPROM saves settings in smart cards and car systems. For example, EEPROM is used in car key fobs to keep security codes safe. EPROM is found in old video game cartridges where updates were rare. PROM works in microwave ovens to hold cooking programs.

? Note: If you want to change your device’s settings a lot, pick EEPROM. If you need simple, permanent storage, PROM is best. EPROM is good for testing and small updates.

You have learned how PROM, EPROM, and EEPROM are different. Each memory type works best for a certain job. Look at the table to see which one to use:

Memory Type	Key Characteristics	Application Scenarios
PROM	Programmed once, cannot change data	Best for fixed data that never needs updates
EPROM	Erased and reprogrammed with UV light	Good for rare updates or testing
EEPROM	Erased and reprogrammed easily, no chip removal needed	Perfect for frequent updates, like firmware or BIOS

Think about how much you need to change your data. Pick the memory type that fits your project. If you are not sure, ask someone who knows or read more about it.

 

 

 

 

 

Written by Jack Elliott from AIChipLink.

 

AIChipLink, one of the fastest-growing global independent electronic   components distributors in the world, offers millions of products from thousands of manufacturers, and many of our in-stock parts is available to ship same day.

 

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