RAM, SAM, ROM, and Types of ROM

There are many types of memories. Some of the memories are mentioned below;

            Random Access Memory(RAM)

            Sequential Access Memory(SAM)

            Read-Only Memory(ROM)


It refers to a bad class of semiconductor memories designed for applications where the ratio of reading operations is very high. Technically, a ROM can be written into (programmed) only once and this operation is normally performed at the factory. Thereafter information can only be read from the memory. 

Figure: ROM

Other types of ROM are read-mostly memories (RMM) which can be written into more than once but the write operation is more complicated than the read operation. Therefore the write operation is not performed very often. This type of memory is designed to hold information that is either permanent or will not change frequently. During normal operation, no new data can be written into a ROM, but data can be read from ROM.

For some ROMs, the data can be entered electrically. ROMs are used to store programs that are frequently required and are not to change during the operation of the computer. Because all ROMs are non-volatile, these programs are not lost when the computer is turned off. One of the main functions of the program stored in ROM is to make the computer ready for operations.


There are primarily three types of read-only memory. ROM refers to IC chips that are masked or programmed by the manufacturer.


A PROM(programmed Read Only Memory) is a semiconductor chip that is obtained from the manufacturer in an unprogrammed state and the user programs it according to its desire. A PROM is programmed outside of the circuit where it is to be used and many commercially available machines, called prom programmers are used to program it.


EPROM is a kind of ROM in which instructions are erased with the help of electrical waves.


Another type of ROM is called Electrically Erasable PROM or EEPROM is also being used for ROM applications. The EEPROM can be altered while being used in a logic board by using special power circuits and write pulse generators. The EEPROM can work as a read/write semiconductor memory while retaining the non-volatile nature of ROMs and PROMs.

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