Read Only Memory (ROM) || B Tech , BCA , BSc || #ddu

#Computer

Read Only Memory (ROM) || B Tech , BCA , BSc || #ddu

#Computer

ROM stands for Read Only Memory, that is, nothing can be written on it. ROM is a non-volatile memory; the information stored on it is not lost when power goes off. It is used for storing the bulk of the programs that are permanently resident in the computer. The contents of ROM are decided by the hardware manufacturer. The necessary programs are hardwired during the manufacture of computer. It also possesses random access property and stores information which is not subject to change.

ROM is used for storing an initial program called a “Bootstrap loader”. This is a program whose function is to start the computer operating system when power is turned ON. Since RAM is volatile, its contents are destroyed when power is OFF. The contents of ROM remain unchanged after power is turned OFF and ON again. When power is turned ON, the hardware of the computer sets the program counter to the first address of the bootstrap loader. The bootstrap program loads a portion of the operating system from disk to main memory and control is then transferred to the operating system.

ROM is divided into four types. They are distinguished by the methods used to write new data to them and the number of times they can be rewritten. Common feature of these devices is their ability to retain data and programs, even during a power failure. ROM comes in following types:

1.     Programmable ROM  PROM has been programmed once,its content can never be changed. As a result, PROM is known as one-time programmable (OTP) device. To write the data on the PROM chip, a device knoen as PROM programmer or PROM burneris required. It is mostly used in video games and electronic dictionaries.

2.     Erasable PROM  EPROM is a type of ROM in which data can be erased or destroyed using Ultraviolet Light (UL). EPROMs arfe used to store programs which are permanent but need updating. Note that an EPROM eraser is not selective; it will erase the entire EPROM. It is more expensive than PROM.

3.    Electrically Erasable PROM  EEPROM is a type of ROM in which data can be erased or destroyed by exposing it to an electric charge. The chip can be erased and reprogrammed on the board easily on a byte by byte basis, rather than erasing the entire chip with ultraviolet light. Hence, the process of re-programming is flexible, but slow.

4.    Flash ROM  Flash ROM is a type of EEPROM, that can be erased and re-programmed in blocks (rather than byte). Flash memory is often used to hold control code such as the BIOS in a personal computer. This memory is mainly used in the memory cards of mobile phones, digital cameras and ipods for storing data.

Topic Covered :

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