Different Types of ROM
- PROM – Stands for the programmable read-only memory. It stores programs permanently and it is a non-volatile memory. Programming the ROM is something referred to as burning and it requires a special machine called a device programmer or ROM burner. Each binary 1 bit can be thought of like a fuse; when a PROM is programmed, a higher voltage blows or burns the fuses at the desired locations thus turning any given 1 into a 0. For this reason, PROM chips are often referred to as one-time programmable (OTP) chips.
ex- CD or DVD is an example of PROM chip
- EPROM – EPROM is the short form of erasable programmable Read-Only Memory. Ultra-violet (UV) rays can erase the programs from this memory. It can be easily recognized by the clear quartz crystal windows set on the top of the chip. An EPROM eraser is the device that contains a UV light source that erases the chip by causing a chemical reaction, which essentially melts the fuses back together.
Ex- Rewritable CD or DVD
- EEPROM/Flash ROM – EEPROM is the short form of Electrically Erasable Programmable Read-Only Memory. Electrical signal removes the programs from this memory. EEPROM can be erased by an electric field, rather than to exposure to UV. Also, the data can be removed bit by bit allowing only selected portions of the code to be replaced. But in the case of flash ROM, data is generally rewritten in blocks of 512 bytes instead of bit by bit, so rewriting is faster. Flash memory can be erased or reprogram block of bytes whereas EEPROM erases individual bytes. This also called hybrid memory as it read and writes data similar to the RAM but, maintains data similar to the RAM but, Maintains data similar to the ROM. It is a mixture of RAM and ROM
Ex- Pendrive, micro SD memory card etc.