Different Types of ROM

ROM is Read-Only Memory and the most important type of electronic storage, which comes in-built to the device during manufacturing. You must have seen ROM chips in your computers and other electronic products; game consoles, VCRs, and even car radios all of them use ROM for completing their functions effectively and smoothly.

ROM chips generally come built-in the external unit – just like flash drives or other auxiliary devices –and are installed in the hardware of a device on the removable chip. The non-volatile memory of ROM stays viable even without the power supply. In this post, we will learn more about ROM and different types of ROM to check out:

What is ROM

ROM is a solid-state memory that will read-only data stored. Its feature is that when data gets stored, it will not be changed and deleted. As mentioned before, it is mainly used in the computer and various electronic devices, even though the power gets turned off, data won’t disappear. The widely used type of primary storage is a volatile form of RAM or random access memory that means content present in RAM can be lost if power gets turned off.

Though ROM is a type of non-volatile memory, it’s not appropriate for use as the primary storage because of some limitations. Generally, the non-volatile memories can be expensive, have got lower performance, and have a limited lifetime when compared to the volatile RAM.

How Does ROM Work?

For its important characteristics like data stored in a ROM is written after manufacture to be read during its working process, rather than being rewritten fast and conveniently like the random memory.

Thus, whatever data gets stored in a ROM will be stable, and stored data will not change even after the power is off; this structure is simple, and reading is convenient, therefore it is used for a task of secondary storage, and long-term storage to store different fixed data and programs.

The CPU reads data only in ROM and traditionally, it has not been possible to modify any data in ROM. But, some ROM chips have rewrite abilities, so data can easily be erased from different kinds of ROM. But, data cannot be rewritten and erased nearly as fast as with RAM.

Way ROM Work During the Bootstrapping Process

Whenever you press a power button, the BIOS chip awakens & checks the different components of the system to ensure they are present and working in the right way. In the process known as a power-on test, BIOS instructs your CPU to check code at various locations. During this test, you may hear the whining of the hard drive & see flashing lights. After this test is done, CPU takes over & launches an operating system.

Different Types of ROM

Different Types of ROM

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Now, let’s go ahead and discuss different kinds of ROMs and their characteristics.

MROM (Masked Read Only Memory)

The first ROMs were the hard-wired devices, which have the pre-programmed data set and instructions. These types of ROMs are called as masked ROMs that cheap.

PROM (Programmable ROM)

PROM can easily be modified once by the user. They can buy the blank PROM & enters desired contents by using the PROM program. Inside a PROM chip, there’re small fuses that are burnt open at the time of programming. This can be programmed just once and cannot be erased. The blank PROM chip enables current to run over all possible pathways, and the programmer selects the pathway for current just by sending the high voltage over unwanted fuses for “burning” it out. Static electricity will create a similar effect by accident, thus PROMs are highly vulnerable to damage than conventional ROMs.

EPROM (Erasable & Programmable ROM)

EPROM can easily be erased just by exposing this to the ultra-violet light and that also for around 40 minutes. Generally, an EPROM eraser attains this function. During the programming, the electrical charge gets trapped in the insulated gate area. This charge can be retained for over 10 years because the charge has got no leakage path. To erase the charge, the ultra-violet light will be passed through the quartz crystal window. And this exposure to UV light dissipates its charge. During normal use, the quartz lid gets sealed with the sticker and this exposure renders a chip blank again, then you may reprogram it as per the similar process as the PROM. The EPROM chips can wear out eventually, however they often have lifetimes of more than 1000 erasures.

EEPROM (Electrically Erasable & Programmable ROM)

EEPROM can be programmed & erased electrically. This type of ROM can be erased & reprogrammed around ten thousand times. Erasing & programming take 4 – 10 milliseconds. In the EEPROM type, any location is selectively erased or programmed. Also, EEPROMs can get erased just 1 byte at a time, instead of erasing the whole chip. Thus, the reprogramming process will be flexible and slow.


It’s the advanced EEPROM version and stores information in the arrangement or range of the memory cells that are made from the floating-gate transistors. One primary benefit of using such memory is you may delete and write blocks of the data over 512 bytes at one time. While, in EEPROM, you may delete or write just 1-byte data at a particular time, thus, this memory type is much faster than the EEPROM.

This memory can be reprogrammed without even removing this from your computer. The access time is a bit high, over 45 – 90 nanoseconds. It’s highly durable since it can easily bear high temperature & intense pressure.

Some Examples of ROM

There’re a few real-life ROM examples, let us see each one:

  • ROM is used in electronics devices such as feature phones Nokia 3310, Handy Games, DVD, VCR, Digital Watches, or more.
  • Because of the permanent data storage, ROM can be used in different kinds of the embedded system as in the embedded system, it doesn’t need changing data.
  • It can also be used in automobiles, where you need data, so data will be saved in a chip.
  • ROM can also be used in various home appliances like microwave, TV, washing machine, refrigerator, and more.
  • ROM can be used in automation toys like singing fish toy and in this particular toy, you can store the preplanned program when push the buttons to generate music.
  • It’s used in various other devices like printers, calculators, FAX machines, plotters, etc.

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