Read only Memory (ROM)

What is ROM (Read only Memory)?

ROM is the abbreviation of Read only Memory. This is a non-volatile memory used in computers where the information is permanently stored.

A ROM can be used in different electronic devices other than computers which actually act as a storage medium. The operating process of it is based on Bootstrap.

Understanding ROM (Read only Memory) in Computer

What is ROM

ROM or Read only Memory is a storage device. Used in computers and other electronic devices, the ROM stores data permanently but the data can only be read but not modified or re-written.

The primary objective of the ROM is to start a computer or to boot it up along with the other programs and software installed in the system. This task is completed with the help of the data stored in the ROM.

Therefore, a ROM can be ideally termed as a storage device that helps a computer system to start up.

The basic job of the ROM is to store the data and software instructions securely and permanently, and, in addition to that, its job also involves doing the major input and output tasks.

Being a Read Only Memory, a ROM is a permanent or non-volatile storage device. This means that the data in it will be stored even if you are not using the computer.

Depending on the make and model of the computer system, the ROM chips may be in different places in the motherboard. In a few specific models, it can also be on the expansion board. The function of these chips is:

As of now, there are many different types of non-volatile memory used in the computer systems.

Each has a distinct specification and comes with different features that determines its functionality. Few of these are even programmable ROMs.

However, if you look at the history of ROMs, the original form of non-volatile memory is the mask-programmed ROM or MROM.

This was specifically designed for a particular data Bootstrap. This usually contained the start-up code. However, the programs of the mask ROM cannot be changed.

The primary objective of this read only mode of program is to activate the Firmware. This is the specific software program or instructions that are installed in the hardware device.

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The ROM provides instructions and determines how a device should perform its task in collusion with other hardware components in it.

This Firmware programs cannot be changed and includes:

ROM is also used in the Optical Storage Media which is usually found in the compact discs such as the Compact Disc Recordable, commonly called CD-R, and the CD-RW or Compact Disc Rewritable.

This specific type of software is known as CD-ROM.


ROM is just like the cartridge used in video game consoles which help the user to play the game either alone or a part of a team who are connected to the game.

The ROM also means a device that has a specific file or software.

This file is actually stored in the EEPROM of the Flash Memory.

EEPROM is ideally the program of ROM which is used in the BIOS of the computer. This is also a variant of ROM.

The ROM consists of the Internal Electronic Fuses, or IEFs. All these fuses can be programmed for a particular interconnection.

In addition to that, there is also a specific chip in the ROM that is designed to store the binary information.

This chip has a few specific characteristics and functionality such as:

The most significant attribute of this non-volatile memory is that it can keep the information stored even when the power of the system is turned off.

It is for this reason a ROM is also referred to as a Programmable Logic Device or PLD.

The programming of the Read Only Memory helps in storing the data in bits in the hardware.

When you switch on the computer the information is sent from the ROM hardware to the RAM as bits.

The functionality of the ROM is very important for a computer.

You may have noticed that when you switch on your computer it does not start off immediately.

In fact, the screen is black and blank for some time.

This is because the computer hardware needs to read the start-up instructions and follow it.

It is these instructions that are actually stored in the ROM.

The instructions help in booting the system, or start the computer, in layman’s terms, and there is a specific process for it.

The hardware of the ROM is also used to store other software programs and sets of instruction for other different components of the computer such as:

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All the relevant information is stored in the flash ROM of the hardware. According to the information stored, further instructions are given to the device.

The Read Only Memory has four output lines that contain four bits of instructions in each.

The instructions are then accessed and determined from the 6 input lines.

This function is overseen and facilitated due to the fact that the ROM has specific addresses for each.

This helps in establishing a communication with the different components of the computer system and enabling an interaction with the other devices.

Types of ROMs

There are different types of ROM and each has its own specific characteristics. These are:

Short for the Masked ROM, these are the first ROMs that were designed. These are inexpensive and hard-wired devices. These ROMs came with a distinct set of instructions and data installed in it.

All these were pre-programmed. The masked ROM is also known as diode matrix and cannot be changed electronically once it is manufactured.

However, the principle of the unattached circuits can be changed by adding the bode wires to replace the components.

However, you cannot change the ICs even then. Therefore, for any update of the software or correction of errors, a new device is required to be manufactured.

This is the short form of Programmable Read only Memory. These ROMs have a unique feature that allows the users to modify the data or instructions but only once.

The PROM chip consists of fuses which are opened during the programming. However, it can be re-programmed only once, after which it will be non-erasable.

This stands for the Erasable Programmable Read Only Memory. This specific type of ROM can modify or erase the program when it is exposed in UltraViolet light for at least 40 minutes.

When the programming is done in EPROM, there is an electrical charge sent that gets trapped in the insulated gate area. This can actually last for more than 10 years.

This is because there will be no leakage in its path. However, to remove the electrical charge you will need to pass the ultraviolet light through the quartz crystal lid. This quartz crystal lid is actually sealed with the help of a sticker.

A short for Electrically Erasable and Programmable Read Only Memory, the name suggests that both programming and erasing are done electrically. It can be re-programmed ten thousand times.

These two functions can be completed in just about 4 to 10 milliseconds. You can erase or program an EEPROM by selecting it from any location.

However, you will be able to erase only 1 byte of data at a particular time and not the entire chip at once. This is the reason the re-programing of this chip is far more flexible but it operates very slowly.

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This is the advanced version of EEPROM. This is actually a modification of the Flash ROM. This stores the information and data in an organized memory cell that is made out of floating gate transistors.

This memory helps to write or delete 1 byte of data at a time. However, the speed at which this task will be performed will be much higher than the standard EEPROM.

This specific ROM is used in storing and transferring data from a personal computer and other digital devices. You will find these advanced ROMs in MP3 Players, USB flash drivers, Digital Cameras and many more.

Functions of ROM

The main function of the ROM is to store data and send it when you start your computer. These stored data can only be read and cannot be edited.

Since the ROM is non-volatile and the data or instructions are stored permanently in it, the data is intact and available as and when required.

The ROM helps in booting the computer with the help of the important programs stored in it. Apart from starting up the computer, the ROM and the data stored in it performs other important functions as well. These functions include:

All these are done using the data that remains stored in the ROM even when the computer is switched off.


ROM or Read-only Memory is a non-volatile storage device used in computers and other electronic devices that stores data permanently but can only be read and not modified or re-written.

The main purpose of the ROM is to boot up a computer along with other software programs installed in it.

There are different types of ROMs available, each with a different set of features and functionality.

The history of ROMs shows that the original form of non-volatile memory is the mask-programmed ROM or MROM.

The ROM is also used to store other software programs and sets of instruction for different components of the computer.

Its functionality is very important for a computer as it stores the start-up instructions and other software programs, and determines how a device should perform its task in collusion with other hardware components in it.