What are RAM and ROM? How are they alike? How are they different?

Q. What are RAM and ROM? How are they alike? How are they different? What are EEROM, PROM and EPROM?

Answer :-

RAM (Random Access Memory):-

It is a read/write memory as it is possible to both read from and write to location within RAM. It is used for primary storage in computers to hold active information of data and instructions. The RAM is a volatile memory as it loses its contents when the power is switched off or interrupted.

ROM (Read Only Memory):-

It is a read-only memory, i.e., the data and instructions are placed in the ROM at the time of its manufacturing and can't be changed thereafter.
ROM is slower than RAM and is used to hold certain essential instructions to check basic hardware components such as booting, procedures to load operating system, and frequently-needed functions.

• They are alike because both RAM and ROM are parts of primary memory.

PROM :-
Programmable Read Only Memory (PROM) is a ROM that can be programmed to record information using a facility known as PROM-programmer. Once the chip has been programmed, the recorded information cannot be changed i.e., PROM becomes same as ROM.

EPROM :-
Erasable Programmable Read Only Memory (EPROM) is another type of ROM that can be erased and the chip can be reprogrammed to record different information using a special PROM-program facility. Erasure is achieved by exposing the chip to ultraviolet light. When an EPROM is in use, information can only be "read" and the information remains on the chip until it is erased. EPROM are of two kinds - UPROM (ultraviolet PROM) and EA-PROM (Electrically Alterable PROM).

EEPROM :-
Electrically Erasable PROM (EEPROM). This type of ROM can be programmed and erased by electrical signals. Information loaded in this memory can be retained for many years without any power supplied; one of its new applications is as a back-up to RAM memory whose contents are lost in a power failure. When power is returned, the EEPROM memory can be used to replace the lost contents of the RAM memory and the microcomputer can continue working just as if nothing had happened. Even newer devices are combining RAM and EEPROM memory in a single integrated circuit.