Difference Between PROM and EPROM

In computers and other electronic devices, there is an internal storage device called ROM (Read Only Memory). It is a storage device used to store data and instructions permanently. Till date, there are several types of ROMs available such as PROM, EPROM, and EEPROM. There are several differences among all these types of ROMs depending on the manufacturing process, electronic components used, operation, reversibility, etc.

In this article, we will discuss the important differences between PROM and EPROM by considering different parameters. But before that, it is important to get an overview of their basics so that it becomes easier to understand the differences between them.

What is PROM?

PROM stands for Programmable Read Only Memory. It is a slightly advanced variant of ROM in which data can be written at once and can be read many times. Thus, it is also referred to as a WORM (Write Once Read Many) type of memory.

PROM is used in several digital devices and systems to store permanent data and information, usually firmware. PROM is manufactured blank and can be programmed at later using a suitable technology. The device used to program the blank PROM chip is called a PROM programmer.

The primary use of PROMs are in mobile phones, microcontrollers, video game consoles, and in many other automotive electronic devices.

What is EPROM?

EPROM stands for Erasable Programmable Read Only Memory. EPROM is also a type of ROM (read only memory) whose data can be erased optically. Similar to the PROM, EPROM is also manufactured blank and programmed as per requirements. It is a type of computer memory that retains its data and information when its power supply is switched off. Hence, it is a non-volatile computer memory. EPROM is built up of metal-oxide semiconductor (MOS) transistors.

The unique feature of EPROM over PROM is that it can be erased many times and can be programmed again. But, to erase data on the EPROM, it is exposed to a strong source of ultraviolet light like mercury-vapor lamp. EPROMs have a resin (or fuse quartz) window in its construction on the top of the package, through which the IC chip is visible, and can be exposed to ultraviolet light for erasing. EPROMs were extensively used in some microcontrollers before the development of EEPROM and flash memory to store on-chip programs.

Difference between PROM and EPROM

Both PROM and EPROM are types of ROM (Read Only Memory), however there are several differences between them that are listed in the following table −

Parameter PROM EPROM
Full Form PROM stands for Programmable Read Only Memory. EPROM stands for Erasable Programmable Read Only Memory.
Reuse PROM is not reusable. It can be written only at once. EPROM is a reusable ROM as it can be erased and written many times.
Cost PROM is a relatively less expensive type of ROM. EPROM is expensive in comparison to PROM.
Reversibility Once a PROM has been processed, it cannot be reversed. Thus, it stores data permanently. The processes of EPROM can be reversed.
Storage Endurance Storage endurance of PROM is very high. The storage endurance of EPROM is higher in comparison to PROM.
Preservation PROM is completely sheathed in a plastic cowl. EPROM is boxed in a rock crystal window so that ultraviolet radiation rays can transfer through it.
Nature PROM is a WORM type memory, which means it is a write once read many type of memory device. EPROM is a type of ROM that is read and write many times.
Writing error reversibility If there is an error or bug while writing on PROM, it cannot be changed-making it unusable. If there is an error or bug while writing to EPROM, it can be reversed, and used again.
Version PROM is known as the older version of EPROM. It can be considered as the modern version of PROM.
Flexibility & Scalability PROM is better than EPROM in terms of flexibility and scalability. It is less flexible and scalable in comparison to PROM.
Main Electronic Component PROM is constructed by using bipolar junction transistors. EPROM is made up of MOSFET (Metal Oxide Semiconductor Field Effect Transistor).


The most significant difference between the two memories is that PROM (Programmable Read Only Memory) cannot be erased once it is programmed, whereas EPROM can be erased many times using a strong ultraviolet light.