ROM (read only memory)...

ROM (read only memory)

• ROM is read only memory it is also random access , but only for read.
• ROM is typically used to store thing that will never change for the life of the computer , such as low level portion of an operating system.
• computer almost always contain a small amount of read only memory that hold instruction for starting up the computer.
• it is non_volatin which means once you turn off the computer the information is still there.

 Main three type of ROM:

1.PROM (programmable):Using the program

2.EPROM (erasable programmable):first erased and reprogrammed.

3.EEPROM (electrically erasable programmable):using electrical lesser.

1.PROM (Programmable read only memory):

A PROM is a memory and it is  data can be written only once.

Once a program has been written onto a PROM , its remain there forever.
PROM is manufactured as blank memory.

2.EPROM (Erasable programmable read only memory):

EPROM is a one type of PROM that can be erased by exposing it to ultraviolate light.

once it is erased,its can be reprogrammed.

3.EEPROM (Electrically Erasable programmable read only memory):

EEPROM is a same as the flash memory. 
This make memory faster.

It is also called flash EEPROM.