What is ROM in Computer and Its Types

What is ROM in Computer and Its Types, Types of read only memory in computer, advantages and disadvantages of (ROM) read only memory, geeks help

What is ROM?

ROM stand for "Read Only Memory". ROM is a non-volatile type of computer memory. This type of computer memory is used to store the data which is permanently written during the manufacturing process. The data which is written during the manufacturing process cannot be easily modified or erased by normal computer operations.

Types of Read-Only Memory in Computer

There are different types of ROM with varying levels of permanence. Here is the list of ROM: 

1. Mask ROM (MROM)

In ROM the data is physically programmed during the manufacturing process. And that creates permanent connections and this type of ROM cannot be changed once programmed. This type of memory was not so expensive it was the very first ROM that consists of a grid of word lines.

2. Programmable ROM (PROM)

This type of memory is a form of Digital Memory. And in this memory, each bit is locked by a fuse or an anti-fuse. In PROM users or manufacturers can program data onto the chip using special equipment. However, once programmed, the data cannot be changed or erased in PROM. This type of memory is used in low-level programs like firmware or microcode.

3. Erasable PROM (EPROM)

In this type of memory, the data can be programmed onto the chip and erased using ultraviolet (UV) light. The EPROM is also called EROM and it is a type of PROM but it can be reprogrammed. PROM allows for limited reprogramming, but the process is time-consuming and requires special equipment.

4. Electrically Erasable PROM (EEPROM)

This type of ROM can be erased and reprogrammed using electrical signals. It is more flexible than EPROM but slower and has limited erase/write cycles. This type of ROM is used in microcontrollers and remote keyless systems. In this type of memory, the duration of erasing and programming EEPROM is about 4ms to 10ms.

5. Flash Memory

Flash Memory technically is not a type of ROM, but it is non-volatile and can be electrically erased and reprogrammed. Flash Memory is widely used for storage in devices like USB drives, SSDs, and memory cards.

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Block Diagram of ROM

Block Diagram of ROM

There are 'n' input lines and 'm' output lines in the ROM block. The input variables' bit combinations are referred to as addresses. Words are the name given to each bit combination that leaves the output lines. The number of output lines, m, is equal to the number of bits per word.

A binary number's address is one of the addresses of one of n variables. Therefore, there are 2n potential addresses for 'n' input variables. An output word has a specific address, and as ROMs have 2n different addresses, there are 2n distinct words in each ROM. The address value applied to the input lines determines the words on the output lines at any given time.

Advantages and Disadvantages of ROM


  • ROM is cheaper than RAM, and it is non-volatile memory.
  • It is easy to test.
  • It is more reliable compared to RAM.
  • Its circuit is more simple compared to RAM.
  • ROM doesn't need refreshing time.

  • In ROM, the data cannot be easily modified so it's an effective way to store sensitive information.


  • ROM is read-only memory so it cannot be changed.
  • ROM is slower compared to  RAM.

  • ROM has limited storage capacity.

  • Sometimes the manufacturing process for certain types of ROM can affect the production timeline of devices.

Features of ROM

1. Non-Volatile Memory: ROM is a non-volatile type of memory so when the power source is turned off, ROM still holds onto its data.

2. Permanent Data Storage: In the ROM the data is written during the manufacturing process and is not easily modified or erased by normal computer operations.

3. Firmware Storage: ROM is commonly used to store firmware, which is software closely tied to the hardware of a device.

4. Boot Instructions: A computer accesses the boot instructions which are stored in ROM when it first starts up. These instructions initiate the process of loading the operating system (OS) and other essential software components.

5. Reliability: ROM contents are fixed during the manufacturing process, it eliminates the risk of accidental data corruption or loss that might occur in writable memory types like RAM or flash memory.

6. Embedded Systems: It is a common option for software storage in embedded systems, which are specialized computers made for particular functions or purposes. ROM is frequently used to store control software and firmware in devices including appliances, industrial machinery, and medical equipment.

7. Security and Protection: ROM has read-only nature which can be leveraged to store sensitive information and critical instructions that must not be altered. This can help protect against unauthorized modifications and tampering.

8. Data Stability: ROM provides stable and consistent data storage, which is important for maintaining the functionality of a device over time.

9. Ease of Integration: ROM chips are relatively simple to integrate into electronic devices and systems due to their fixed data storage characteristics.

FAQs on Read-Only Memory

Question-1: What is Read-Only Memory (ROM)?

Answer: Read-Only Memory (ROM) is a type of computer memory that stores data permanently. And it is a non-volatile type of memory.

Question-2: What is the purpose of ROM in a computer?

Answer: ROM serves several purposes in a computer, including storing firmware, which contains low-level instructions for hardware initialization and system booting. ROM also holds essential instructions that help start the computer when powered on.

Question-3: How is ROM different from RAM?

Answer: ROM and RAM both are types of computer memory. But ROM is a non-volatile type of memory and RAM is a volatile type of computer memory.

Question-4: What types of data are commonly stored in ROM?

Answer: ROM commonly stores firmware, boot instructions, and essential software routines.

Question-5: Can data in ROM be changed or updated?

Answer: Data in traditional ROM cannot be changed or updated after manufacturing. However, some variations of ROM allow for limited reprogramming and these are Programmable ROM (PROM), erasable PROM (EPROM), and electrically erasable PROM (EEPROM)

Question-6: What are the advantages of using ROM?

Answer: The advantages of using ROM include non-volatile storage, security for critical data, reliability, stability, and fast data retrieval.

Question-7: What are the disadvantages of using ROM?

Answer: The disadvantages of using ROM include its immutability, limited flexibility for updates, potential waste if obsolete, higher development costs, and limited storage capacity.

Question-8: Can ROM be used for data storage in modern computers?

Answer: While ROM is not the primary choice for data storage in modern computers, it still plays a crucial role in storing firmware and boot instructions. More modern non-volatile memory technologies like flash memory and solid-state drives (SSDs) are commonly used for data storage.

Question-9: Is ROM used only in computers?

Answer: No, ROM is used in a wide range of electronic devices beyond computers, including appliances, industrial equipment, gaming consoles, mobile phones, and more.

Question-10: How is flash memory related to ROM?

Answer: Flash memory is a type of non-volatile memory that can be electrically erased and reprogrammed. While not technically a type of ROM, it shares some characteristics with ROM, such as non-volatility, and is commonly used for data storage in various devices like USB drives, SSDs, and memory cards.

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