What is Read Only Memory (ROM)?

what is read only memory
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There is different storage option on computers and other such electronic devices one of which is Read Only Memory (ROM). It is one of the safest means for storage as data once stored in ROM cannot be altered. It is mainly used to store instruction and other such data which are constant.

ROM is one such storage which does not lose data even after power supply is turned off. ROM is also known as non-volatile memory data stored in chip remains the same and does not get erased even if power is cut off.

Working of ROM

ROM is also known as firmware as it has some data which are stored in the circuit through programming at the time of manufacturing. It is very difficult to rewrite ROM’s chip and so manufacturers make sure that perfect data is written on it.

Today there are ROM chips which give the option to reprogram but it is a very slow and time-consuming task. It may even interrupt the security of data and so manufacturers always avoid to reprogram data stored in ROM.

The type of data which are mostly stored in ROM is BIOS, Bootstrap process, software instruction and many more. These are some instructions which are not required to be changed and so writing them in ROM can make it permanent for devices. ROM is used in compact discs like CD-R, CD-ROM, etc.

Also read – Type of computer memory

Classification of ROM

ROM is mainly for storing non-volatile data. Today there are different types of ROM that are differentiated depending on their functionality.

  • PROM

It is also known as programmable ROM where users can burn information as required. It is also known as a One-time programmable memory where data can be fused just once and if it is inappropriate PROM should be discarded. During manufacturing, it has blank memory where data is to be written later.

Users are required to very careful while infusing data on this type of ROM as data once written cannot be changed. There is a need for special equipment like a ROM burner or ROM programmer to write programs.


As the name suggests Erasable programmable ROM where data can be changed after the content is written in PROM. It gives the option where data erasing and rewriting can be done a thousand times but the only problem is the time-consuming task.

It is mainly used while working on a microprocessor type of project. This type of ROM is also known as UV-EPROM as it uses ultraviolet radiation to erase content written on ROM. Data cannot be erased when EPROM is installed in system board and so it has to be removed for changing.


It removes the disadvantage of EPROM and so known as Electrically erasable programmable Remit can erase data electrically and so takes less time as compared to UV-EPROM. It gives the option to erase and rewrite data while ROM is in system board itself.

EEPROM allows to select the byte which is to be erased and thus complete data is not required to be removed. The cost of erasing and reprogramming is quite high in EEPROM compared to EPROM.

  • Flash Memory EPROM

It is semiconductor memory which is the same is EEPROM where without removing form socket it is possible to erase and rewrite data. It is divided into blocks so it is possible to erase the block and rewrite accordingly. It gives more chances to erase and write data as compared to EPROM and EEPROM. It is used when there is a need to upgrade BIOS of the device.

  • Mask ROM

It is just like the basic ROM where data is written by IC manufacturers itself. It is used when high volume permanent data is to be written on ROM.

It is quite cheaper as compared to other and is used when finalized data of the project is to be written.

Also read – What are Peripheral Devices of a Computer?

The Bottom Line

In computer and other electronic devices, permanent storage ROM is preferred. There was a time when ROM chips were used only in computers but today many electronic devices come with ROM for storage. As mentioned above there are different types of ROM which have its own characteristics and use. ROM can operate at an electronic speed and is a very important part of electronic devices.

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