Read Only Memory (ROM): Definition, Types, Features, Differences

Memory

Memory is basically a device that has the capacity to store information. Moreover, it is the most important component of a computer system as it cannot perform even simple tasks without it. Basically, computer memory is of two types namely, primary memory (Random Access Memory (RAM) and Read Only Memory (ROM)) and secondary memory (CD, DVD, hard disk, etc). Let us study the read only memory in detail.

Read Only Memory (ROM)

As the name suggests, we can only read from this memory and cannot write on it. Moreover, it is non-volatile in nature which means that it does not lose data after the power supply is cut off. Furthermore, its main function is to store the program and instructions which are important to boot (start) the system. This is the bootstrap process.

Other than computers, many devices like calculators, washing machines, ovens, etc use the ROM.

Features of Read Only Memory

The ROM has the features as follows:

It is non-volatile in nature.
Less costly than the RAM.
As, only read operation is allowed therefore, no changes can occur.
It is easy to test the ROM.
Due to its nature, it is more reliable than RAM.
Does not require any refreshing.

Types of Read Only Memory

There are 4 types of ROM out of them, 3 are the most common. These are as follows:

MROM (masked read only memory)
PROM (programmable read only memory)
EPROM(erasable and programmable read only memory)
EEPROM(electrically erasable and programmable read only memory)

MROM (Masked Read Only Memory)

These were the very first ROMs. Furthermore, these are hard-wired devices that contain a pre-programmed set of data and instructions. Moreover, they are inexpensive in nature.

PROM (Programmable Read Only Memory)

It is the programmable ROM that the user can program but only once. Furthermore, the user writes the data and instructions using a PROM program. Moreover, after writing once the user cannot change or erase the data and instructions.

EPROM (Erasable and Programmable Read Only Memory)

We can reprogram this memory by erasing the data. Furthermore to erase the data it has to be exposed to ultraviolet light. During the programming, a charge is trapped in the insulated gate region. Besides, on exposing it to the ultraviolet light for around 40 minutes this charge destroys. Hence, in this way, the data gets erased. After erasing the data we can now reprogram the ROM.

EEPROM (Electrically Erasable and Programmable Read Only Memory)

We can program and erase this memory electrically. Furthermore, we do not require any ultraviolet light to erase the data. Moreover, erasing and reprogramming is possible many times. Besides, we can erase any particular location of the memory selectively. At the same time, we can delete only one byte from the memory at a time rather than erasing the whole chip. Therefore, the process of reprogramming is flexible and slow.

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Difference Between PROM and EPROM

PROM	EPROM
PROM is non-reusable.	It is reusable in nature.
Less costly.	More expensive than PROM.
If we write the data once, it is permanent and we cannot erase it.	Data is not permanent, we can erase and rewrite it.
The storage capacity is high.	Storage capacity is less than the PROM.
If there is any error or bug in the PROM’s program it becomes useless as we cannot rewrite it.	Whereas we can erase and fix the previous code in EPROM.
It uses a bipolar transistor.	It uses a MOS transistor.

RAM (Random Access Memory)

RAM stands for Random Access Memory. It is the internal memory in the computer’s CPU which stores different types of data and information as per the requirement. Moreover, we can also call it the main memory, primary memory, or read/write memory. RAM stores all the data that the CPU requires during the execution of a program. Moreover, it is a volatile memory i.e. it loses data as soon as the power is cut off.

Difference Between RAM and ROM

RAM	ROM
It is temporary storage.	It is permanent storage.
Storage capacity is in MBs.	Storage capacity is in GBs.
It is volatile in nature.	It is non-volatile in nature.
Stores the data and information of the programs and applications currently on the system.	On the other hand, it stores programs during the startup of the system.
We can access and change the data.	We can only read the data.
Speed is high.	Speed is much less in comparison to RAM.
It is expensive.	It is less expensive than RAM.
RAM is used as the cache or primary memory.	The firmware uses it as microcontrollers.
Its types are SRAM and DRAM.	Its types are PROM, EPROM, and EEPROM.

Frequently Asked Questions (FAQs)

Q1. What is the full form of ROM?

A1. Read Only Memory

Q2. ROM is:

a) volatile

b) non volatile

A2. b) non volatile

Q3. What is the main function of ROM?

A3. Its main function is to store the program and instructions which are important to boot (start) the system. This is the bootstrap process.

Q4. Where can we use ROM?

A4. Besides, the computer systems, we can use from in calculators, washing machines, ovens and other peripheral devices also.

Q5. What are the different types of ROM?

A5. There are 4 types of ROM out of them, 3 are the most common. These are as follows:

MROM (masked read only memory)
PROM (programmable read only memory)
EPROM(erasable and programmable read only memory)
EEPROM(electrically erasable and programmable read only memory)

Q6. What are the advantages of ROM?

A6. The advantages are as follows:

It is non-volatile in nature.
Less costly than the RAM.
As, only read operation is allowed therefore, no changes can occur.
It is easy to test the ROM.

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Read Only Memory (ROM)

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