All the different memory units inside a microcontroller can be divided into

two main types: RAM and ROM. RAM (from Random-Access Memory) in

microcontroller-based systems is a volatile memory used to store temporary

data such as the system's firmware variables. ROM (from Read-Only Memory) in

microcontroller-based systems is non-volatile memory used to store permanent

data such as the system's firmware.

source

• Flash
• RAM
• EEPROM