What is ROM ? List out the different types of ROM. [2+3]

What is ROM?

ROM (Read-Only Memory) is a type of non-volatile memory used in computers and other electronic devices. Unlike RAM, which loses its data when power is turned off, ROM retains its data permanently. ROM is primarily used to store firmware, bootloader programs, and other critical system instructions that must be available immediately when the device is powered on.

Types of ROM

ROM comes in several varieties, each with distinct characteristics:

1. Masked ROM (MROM)

   • Data is permanently written during manufacturing.
   • Cannot be altered or reprogrammed.
   • Used in applications where data is fixed (e.g., BIOS in older computers).

2. Programmable ROM (PROM)

   • Blank ROM that can be programmed once using a special device called a PROM programmer.
   • Data cannot be erased or rewritten after programming.
   • Used in early embedded systems where custom firmware was needed.

3. Erasable Programmable ROM (EPROM)

   • Can be erased using ultraviolet (UV) light and reprogrammed.
   • Requires removal from the circuit for erasure.
   • Used in development and prototyping stages.

4. Electrically Erasable Programmable ROM (EEPROM)

   • Can be erased and reprogrammed electrically, without removal.
   • Slower write speeds compared to flash memory.
   • Used in applications requiring frequent updates (e.g., firmware storage in microcontrollers).

5. Flash Memory

   • A type of EEPROM that can be erased and reprogrammed in blocks rather than byte-by-byte.
   • Faster and more cost-effective than traditional EEPROM.
   • Used in USB drives, SSDs, and modern BIOS/UEFI systems.

Each type serves specific purposes based on requirements for permanence, rewritability, and speed.