ROM (Read Only Memory) and its type
ROM stands for reading only memory. The memory from which we can only read but can not write on it. This type of memory is non-volatile. This information is stored permanently in such memories during manufacture. A ROM stores such instruction that is required to start a computer. This operation is referred to as bootstrap. ROM chips are not only used in the computer but also in electron items like washing machines & microwave oven.
* Following are Various type of ROM
1) MROM (Masked Read Only Memory):-
The very first ROM were hard-wired devices that contained a pre-programmed set of data or instructions. These kinds of ROM are known as masked ROM which in inexpensive.
2) PROM (Programmable Read-Only Memory):-
PROM read-only memory that can be modified only on by the user buys a blank PROM & enter the desired content using a PROM program. Inside the PROM chip, there are small fuses that are burnt open during programming. It can be programmed only once & is not erasable.
3) EPROM (Erasable & Programmable Read-Only Memory):-
The EPROM can be erased by exposing it to ultra-violet light for a duration of up to 40 minutes. Usually, an EPROM eraser does this function during programming, an electrical charge is trapped in an insulated gate region. The charge is retained for more than ten years because the charge has no leakage path. For erasing this charge, ultraviolet light is passed through a quartz crystal window(lid). This exposure to ultra-violet light dissipates the charge. During normal use, the quartz lid is sealed with a sticker.
4) EEPROM (Electrically Erasable & Programmable Read-Only Memory):-
The EEPROM is programmed & erased electrically. EEPROM can be selectively erased & programmed EEPROM can be erased one byte at a time, rather than erasing the entire chip. Hence the process of re-programming is flexible & slow.
Advantages of ROM
Non-volatile in nature.
These cannot be accidentally changed.
Cheaper than RAM.
Easy to test.
More reliable than ROM.
These are static & do not require refreshing.
Its content is always known & can be verified.