Introduction to Read-Only Memory (ROM)

Last Updated: 2022-06-14

Resumen: ROM is a storage memory medium where the data cannot be changed and modified. This post will give a general introduction to Read-Only Memory (ROM).


ROM (Read Only Memory) is a memory storage device that is non-volatile and stores data permanently. It is also the computer’s primary memory unit as well as RAM (random access memory). Strictly speaking, read-only memory refers to hard-wired memory, which cannot be changed electronically after manufacture.

After users manufactured this memory device, they can only read what is in the ROM, but cannot change or modify the data stored in the ROM. That’s why it is called Read-Only Memory.

ROM is useful for storing firmware. Firmware is the software that is attached to the programmed or hardware on hardware devices and is rarely changed during the system life cycle.


MROM – Masked Read-Only Memory

The MROM is the oldest and original type of ROM, which becomes obsolete and is popular today. MROM is read-only and cannot be modified or reprogrammed, so once the data is on the MROM, no one can change it. Users need to replace the ROM with another device to boot the equipment differently.

PROM – Programmable Read-Only Memory

The PROM is a blank version of the ROM and can only be modified once. PROM is manufactured as unused memory so that programmers can purchase it without any data or information on it.

Users can use a dedicated device called PROM burner or PROM programmer to write information on the PROM chip. Once they have written the data on the PROM, they can not change, modify, or replace the data later.

EPROM – Erasable and Programmable Read-Only Memory

The EPROM is a ROM type that can be modified, reprogrammed, and erased multiple times. But it requires exposure to ultraviolet light (UV light) through special equipment (a quartz window) for up to 40 minutes to delete the data. A device called a PROM burner or PROM programmer is required to reprogram the EPROM.

EEPROM – Electrically Erasable and Programmable Read-Only Memory

The EEPROM is a read-only memory that can be erased and reprogrammed over and over again up to 10,000 times. Users can erase and reprogram it electrically without exposing it to UV light, but the process will be slow as it can be changed one bit at a time.

EEPROM is the most accessible ROM type to modify. Users can change it thousands of times before it no longer works.

Flash ROM

It is a modern advanced type of EEPROM, which stores data in an arrangement or array of memory units consisting of floating-door transistors. This Flash ROM is faster than EEPROM because users can delete or write about 512 bytes of data at a specific time.

What’s more, users and reprogram the Flash ROM without removing it from their computer. And it is highly durable and can withstand intense pressure and high temperature.


  • los ROM is non-volatile memory, while RAM is volatile.
  • ROM chips read data slower than RAM.
  • As for ROM, data is still on it if you turn off the device. And the data can be accessed after you turn on the device again. But as for RAM, all the data will be deleted if you turn off the device.
  • ROM is required to allow the device to turn on properly.
NOTA: There are similarities and differences between ROM and RAM, if you want to know more about RAM, please click another article about RAM to read: Información básica sobre RAM (memoria de acceso aleatorio).


Ultimas palabras

The above content gives some necessary information about ROM. Currently, ROM is essential in many fields, such as microwaves, computers, smartphones, etc. Anything that requires a program to boot will need ROM for this purpose.

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