What is ROM (Read Only Memory) | Types & characteristics of ROM

Hello friends, today we are going to talking about Computer ROM (Read Only Memory).

Today we will learn in detail about, what is Rom? How many types of ROM and what are the characteristics of ROM.

So without wasting time let’s first understand what is ROM?

ROM (Read Only Memory)
What is ROM (Read Only Memory)

What is ROM in Computer

ROM is a memory device used by computer manufacturers to permanently store information inside a chip. Inside a ROM have some important instructions or programs that are required to start or boot the computer.

All the instructions which are required to boot the computer are stored in ROM by the computer manufacturer.

It is a “Non-Volatile Memory” in which the stored data and instructions are not destroyed even when the power is turned off or the system is turned off.

ROM is a long-term internal memory similar to RAM that is directly accessed by the CPU.

It is slightly slower than RAM, so it is cheaper than RAM.

A simple example of a ROM is the cartridge used in video game consoles that allow the system to run multiple games.

Data stored permanently on computers and other electronic devices like smartphones, tablets, TVs, ACs, etc. is also an example of ROM.

ROM is also used to store firmware, which is a software program that is attached to the hardware.

It provides instructions to a computer device to communicate and interact with other devices.

ROM is a ready-only memory, in which the stored data and information can only be read and no changes can be made in it. However, in recent times, some such ROM memory has been developed in which the store information can be changed if needed.

Let’s understand about all these types of ROM memory.

Types of ROM

  1. MROM
  2. PROM
  3. EPROM


The full form of MROM is Masked Read Only Memory. It is the oldest type of read-only memory which is used by the manufacturer to pre-configure the program or data at the time of manufacturing.

The data stored in MROM cannot be modified, reprogrammed, and erased later by the user.

It is a hardware memory device made up of integrated circuits. This is the oldest type of ROM, which is not used in today’s time.


The full form of PROM is Programmable Read Only Memory. PROM is a blank memory that can be programmed later by the user.

This is a blank version of ROM memory that you can buy and program accordingly. But it can only be programmed once, in which the store information cannot be changed anymore. Due to its nature, it is called a one-time programmable device.

PROM programmer or PROM burner is used to store data or information in PROM chip. The process of programming the PROM chip is called burning.

Uses – It is used in cell phones, video game consoles, medical devices, etc.


EPROM is also a type of ROM, its full form is Erasable and Programmable Read Only Memory, as the name suggests, Erasable and Programmable means that the data stored in it can be reprogrammed by erasing it several times.

The data stored in this is not destroyed unless it is exposed to some intense ultraviolet light.

If we want to erase the data stored in the EPROM and reprogram it, then for this we have to pass it in intense ultraviolet light for 40 minutes, this destroys the information located in the EPROM and it becomes programmable again.

A special device like a PROM programmer or a PROM burner is used to reprogram the EPROM.

It is a non-volatile memory chip in which data can be stored for a minimum of 10 to 20 years even if there is no power supply.

Uses – It is used to store programs in some microcontrollers (eg some versions of Intel 8048 and Freescale 7,711).


EEPROM is also a type of read-only memory, whose full form is Electrically Erasable and Programmable Read Only Memory. As the name suggests, Electrically Erasable and Programmable means that the data stored in it can be reprogrammed by electrically erasing it several times.

Data stored in EEPROM can be reprogrammed by erasing it up to 10000 times.

No ultraviolet light is required to erase the data in EEPROM. In this, the stored data can be erased by passing it in a simple electric field, hence it is called EEPROM (Electrically Erasable and Programmable Read Only Memory).

It takes approximately 4 to 10 milliseconds to erase and reprogram the data stored in the EEPROM.

The data of the entire chip cannot be erased at a time in EEPROM, in which only one byte of data can be erased at a time, due to which reprogramming in EEPROM is flexible but quite slow.

Its data access time is between 45 and 200 nanoseconds.

Uses – The BIOS of the computer is stored in this memory.

5. Flash ROM

FLASH ROM is an advanced version of EEPROM that stores information in memory cells made of floating-gate transistors.

In FLASH ROM you can erase 512 bytes of data at a time whereas in EEPROM only one byte of data could be erased at a time, so flash memory is faster than EEPROM.

The data stored in flash memory can be easily erased without removing it from the computer.

Its access time is 45 to 90 nanoseconds, as well as its life is also longer, it can tolerate high temperatures.

It is used to transfer data between personal computers and digital devices.

It is used to store the BIOS of many modern computers on a flash memory chip, called a flash BIOS. It is also used in USB flash drives, MP3 players, digital cameras, modems and solid-state drives (SSDs), etc.

Characteristics of ROM

  • It is a non-volatile memory in which the stored information is not destroyed even after the power supply is turned off.
  • Data can be stored permanently in ROM.
  • It is easier to test and store large data in ROM than in RAM.
  • Data stored in ROM cannot be changed later. However, the data stored in some types of ROMs can be changed if needed.
  • It is cheaper.
  • It is simple and reliable computer memory.
  • It helps to start the computer and load the OS.



Friends, I hope that after reading this article you will know very well about, what is ROM? How many types of ROMs and what are the Characteristics of ROM.

If you want Complete Tutorial of Computer Fundamentals then see this article Computer Fundamental Tutorial | Here you will get all the topics of Computer Fundamentals step by step.

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If you still have any question or doubt related to ROM, then tell me, I will answer all your questions and you can contact us for more information.

Jeetu Sahu is A Web Developer | Computer Engineer | Passionate about Coding, Competitive Programming, and Blogging

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