PROM

 PROM stands for Programmable Read-Only Memory. It is a type of memory device that can be programmed by the user to store data permanently. PROMs are non-volatile, meaning they retain their data even when the power is turned off.

Here are some key features of PROMs:

1. **Read-Only Memory**: PROMs are categorized as read-only memory because, once programmed, the data stored in them cannot be modified or erased. The stored data is fixed and can only be read.

2. **Programmability**: PROMs are programmable by the user. They are initially blank, and the user can use a device called a programmer to burn or program the desired data into the memory cells of the PROM.

3. **Fuse or Antifuse Technology**: PROMs use either fuse or antifuse technology to store data. In fuse-based PROMs, a circuit element called a fuse is selectively blown or "programmed" to represent a binary 1 or 0. In antifuse-based PROMs, an initially non-conducting element called an antifuse is selectively "programmed" to become conducting or non-conducting to represent the desired data.

4. **Non-Volatile**: PROMs retain their programmed data even when power is removed. This characteristic makes PROMs suitable for applications where the data needs to be stored permanently and accessed reliably upon power-up.

5. **Limited Programming**: Unlike other types of programmable memory such as EEPROM (Electrically Erasable Programmable Read-Only Memory) or Flash memory, PROMs can only be programmed once. Once the data is programmed, it cannot be erased or modified.

PROMs have been widely used in various applications where fixed data or firmware needs to be stored permanently. Examples include boot code for microprocessors, firmware for embedded systems, lookup tables for digital circuits, and configuration data for electronic devices.

It's important to note that with the advancement of technology, PROMs have been largely replaced by more versatile and reprogrammable memory technologies such as EEPROM and Flash memory, which allow for multiple programming cycles and greater flexibility in data storage and modification.