MROM(Masked Read Only Memory):

• MROM is the oldest type of read-only memory whose program or data is pre-configured by the integrated circuit manufacture at the time of manufacturing.
• Therefore, a program or instruction stored within the MROM chip cannot be changed by the user.

PROM (Programmable Read Only Memory)

• It is a type of digital read-only memory, in which the user can write any type of information or program only once.
• It means it is the empty PROM chip in which the user can write the desired content or program only once using the special PROM programmer or PROM burner device; after that, the data or instruction cannot be changed or erased.

EPROM (Erasable and Programmable Read Only Memory)

• It is the type of read only memory in which stored data can be erased and re-programmed only once in the EPROM memory.
• It is a non-volatile memory chip that holds data when there is no power supply and can also store data for a minimum of 10 to 20 years.
• In EPROM, if we want to erase any stored data and re-programmed it, first, we need to pass the ultraviolet light for 40 minutes to erase the data; after that, the data is re-created in EPROM.

EEPROM (Electrically Erasable and Programmable Read Only Memory)-

• The EEROM is an electrically erasable and programmable read only memory used to erase stored data using a high voltage electrical charge and re-programmed it.
• It is also a non-volatile memory whose data cannot be erased or lost; even the power is turned off.
• In EEPROM, the stored data can be erased and reprogrammed up to 10 thousand times, and the data erase one byte at a time.

Flash ROM-

• Flash memory is a non-volatile storage memory chip that can be written or programmed in small units called Block or Sector.
• Flash Memory is an EEPROM form of computer memory, and the contents or data cannot be lost when the power source is turned off.
• It is also used to transfer data between the computer and digital devices.

Advantages of ROM-

• It is a non-volatile memory in which stored information can be lost even power is turned off.
• It is static, so it does not require refreshing the content every time.
• Data can be stored permanently.
• It is easy to test and store large data as compared to RAM.
• These cannot be changed accidently
• It is cheaper than RAM.
• It is simple and reliable as compared to RAM.
• It helps to start the computer and loads the OS.

Disadvantages of ROM-

• Store data cannot be updated or modify except to read the existing data.
• It is a slower memory than RAM to access the stored data.
• It takes around 40 minutes to destroy the existing data using the high charge of ultraviolet light.