ROM(Read Only Memory)

ROM : Rom is a read only memory.  ROM is the primary memory of a computer. The instructions and data in the ROM memory are written to the computer while the computer is being written, otherwise the user cannot read and modify the instructions and data in it, so this memory is called read only memory.

          There are some instructions and data stored in Rom, that are needed before the computer can start.  The computer automatically starts receiving such instructions and data as it is turned on automatically.  Nevertheless, it is part of using certain types of programs to continue the process of adoption.Therefore, such memory enhancement is not required as well as it may be harmful to change.  Because of this, the memory is permanently attached to the computer.

Subtypes of ROM :
1. PROM :  Prom is a programmable read only memory.  A PROM is a memory chip on which data can be written at a time.  Some special applications require the user to place their special program in the ROM.  At this point, he can use the prom.  But he needs a special prom burner or prom programmer to write the program to prom.  This allows the user to write programs at a time.  Once written, there is no way to change it.  Only programs written can be read.
          One of the important differences between Prom and ROM is that the Prom is manufactured by Blank Memory.  On which the user can write the program at one time.  But the ROM is a factory-filled memory.  On which the user cannot write programs.  He can only read it.

2. EPROM : EPROM is an erasable programmable read only memory.  Eprom is a special type of memory and the data on it can be wiped with ultraviolet light.  Whenever the ultraviolet light goes through the memory, the bits of that memory are erased and zeroed.  Therefore, programs can be rewritten on such memory using the PRO programmer.  In this way the memory chip can be programmable again.

3. EEPROM : EEPROM is an electrically erasable programmable read only memory.  EEPROM is a special type of memory that can be wiped or written using electrical data. EEPROM is like a flash memory.  Sometimes this is called the Flash EEPROM.
          The important difference between EEPROM and Flash memory is that EEPROM is a single bit writes or reads data.  But flash memory does erase blocks at a time.  Therefore, the speed of comparable flash memory is very high.  When a ROM is electrically erased, it is called an electrically erasable programmable read only memory or an electrically irreversible programmable read only memory.