ROM stands for Read Only Memory which is a memory device or storage device that stores information permanently.

Like random-access memory (RAM), Read Only Memory is also the primary memory unit of a computer.

This is called read-only memory because we can only read its program but cannot write to it.

The ROM builder or manufacturer fills or installs the program in Read Only Memory at the time the ROM is created. Subsequently, content or programs loaded in ROM cannot be changed.

This means that you cannot rewrite nor delete its contents or programs later. However, there are some types of ROMs in which you can modify data.

ROM structure and functioning

The ROM consists of special internal electronic circuits that are programmed for a specific interconnection pattern (information).

The information in the chip is in binary form, the binary information in the chip is specified by the designer and then embedded in the unit at the time of creation to create the required interconnection pattern (information).

Once the pattern (information) is established, it remains within the unit even when the power is turned off. Therefore, it is a non-volatile memory because it holds information even when the power is off.

The information inside the ROM is installed in the form of Bits, this is known as programming the Read Only Memory.

For example, when you start your computer, the screen is not immediately visible. It takes time to appear because the ROM contains startup instructions called BIOS, which are necessary to start the computer during the booting process.

The booting process is to start the computer and check the connection and health of all hardware. It loads the operating system into the main memory (RAM) installed on your computer.

The BIOS program, which is also installed in computer memory (ROM), is used by the computer’s microprocessor to start the computer during the booting process.

This allows you to open the computer and connect the computer to the operating system.

Types of ROM (Read Only Memory)

There are five types of ROM (Read Only Memory)

  1. Masked Read-Only Memory (MROM)
  2. Programmable Read-Only Memory (PROM)
  3. Erasable and Programmable Read-Only Memory (EPROM)
  4. Electrically Erasable and Programmable Read-Only Memory (EEPROM)

Masked Read-Only Memory (MROM)

It is the oldest type of read only memory or ROM. It is no longer in vogue, this technology has become outdated. Therefore it is not used anywhere in today’s world.

It is a hardware memory device in which programs and instructions are stored when the manufacturer makes them. It is therefore programmed during the manufacturing process and cannot be modified, reprogrammed, or deleted later.

This type of ROM is known as Masked ROM, which is inexpensive.

Programmable Read-Only Memory (PROM)

PROM is read-only memory that can be modified by the user only once. The user purchases a blank PROM and inserts the desired content into it using a PROM program.

Inside the PROM chip, there are small fuses that burn during programming. It can only be programmed once and is not erasable. Once inserted the program cannot be deleted.

Erasable and Programmable Read Only Memory (EPROM)

EPROM is a type of ROM that can be reprogrammed and erased multiple times. The method of erasing data is very different; It comes with a quartz window through which a specific frequency of ultraviolet light is passed to erase the data for about 40 minutes.

Therefore, it retains its contents until it is exposed to ultraviolet light. You need a special tool called a PROM programmer or PROM burner to reprogram the EPROM.

Electrically Erasable and Programmable Read-Only Memory (EEPROM)

The EEPROM is programmed and electrically erased. It can be erased and rebuilt about ten thousand times. Both erasing and programming take approximately 4 to 10 ms (milliseconds).

In EEPROM, any location can be selectively erased and programmed. The EEPROM can be erased one byte at a time instead of erasing the entire chip. Therefore, the process of reprogramming is flexible but slow.

The BIOS of the computer is stored in this memory.


This is an improved version of EEPROM. It stores information in an arrangement or array of memory cells made from floating-gate transistors.

The advantage of using this memory is that you can block or delete about 512 bytes of data at a particular time. Whereas, in EEPROM, you can delete or write only 1 byte of data at a time. So, this memory is faster than EEPROM.

It can be programmed without removing it from the computer. Its access time is very long, about 45 to 90 nanoseconds. It is also highly durable because it can tolerate high temperatures and intense pressures.

Advantages of ROM

The advantages of ROM are as follows

  • It is non-volatile, meaning data cannot fly.
  • It cannot be changed accidentally. The way your data flies from other memory by mistake, it cannot happen with it
  • It is cheaper than RAM.
  • Easy to test.
  • More reliable than RAM.
  • No need to static and refresh.
  • The content or program is always known and

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