What are ROM and its types?

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ROM stands for Read-Only Memory. It is a memory device that is used to stored information permanently during the manufacturing process.ROM stores programs that are required to start a computer, this process is known as bootstrapping or tuning of a computer.

ROM is non-volatile in nature as it holds the information even when the power is turned off. It is called read-only memory as we can only read and store the programs on it but cannot write on it. In older ROMs, once data is written on a chip, it cannot be erased or modified. Now, It has the capability to rewrite and erased data. However, data can’t be rewritten or erased as quickly and easily as with RAM.

ROM chips are not only used in the computer but also in other electronic items like washing machines, calculators, and microwave ovens.

How does ROM work during bootstrapping?

ROM holds programs that are needed for operating the computer system and its hardware components such as a keyboard, mouse, printer, etc.

ROM contains BIOS (Basic Input/Output System), and it is also known as Boot Loader. When the computer starts, the BIOS is loaded into RAM and instructs the CPU to checks the various components of the computer to make sure they all are present and working properly. During this process, you might hear the whirring sound of the hard drive. This process is known as the power-on self-test (POST)

Types of ROM

1) MROM(Mask ROM)

2) PROM(Programmable ROM)

3) EPROM(Erasable and Programmable ROM)

4) EEPROM(Electrically Erasable and Programmable ROM)

MROM

Mask Read-only Memory is a full form of MROM. It is the first and inexpensive Read-only memory. It contains a set of data or instructions that can be programmed during the manufacturing process.

PROM

Programmable Read-only Memory is a full form of PROM. PROM is manufactured as a blank memory and data can be written only once by a user.

The user buys a PROM and writes the desired data on it with a device called a PROM programmer or PROM burner. It can be programmed just once by blowing the fuses. This process is known as burning the PROM. It is not erasable.

EPROM

Erasable and Programmable Read-only Memory is a full form of EPROM. As its name suggested, this read-only memory chip has erased the programmed data. It can be programmed to write data with high voltage, and the data remains until it is exposed to ultraviolet light. 

For erasing the data, ultra-violet light is passed through a quartz crystal window (lid). During normal use, the quartz lid is sealed with a sticker.



EEPROM

Electrically Erasable and Programmable Read-only Memory is a full form of EEPROM. The principle of operation in EEPROM is the same as EPROM but the ways to program and erase the memory are different.

In EEPROM, memory is programmed and erased electrically and any location can be select for erased and programmed. Reprogramming in EEPROM is flexible but slow as only one byte can be erased at a time, rather than erasing the entire chip.



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