programminne

Programminne, also known as program memory, is a non-volatile storage area that contains the machine code that a processor fetches and executes. In many embedded systems and microcontrollers, programminne is implemented as flash memory or ROM. Unlike data memory, which stores runtime data, programminne retains firmware even when power is removed. In Harvard-architecture devices the program memory is physically separate from data memory, enabling concurrent instruction fetch and data access; in von Neumann architectures the distinction is logical rather than physical.

Typical program memory holds the device firmware, bootloaders, and sometimes a ROM-based startup code. It is often flash memory that allows in-system programming, meaning the device can be reprogrammed without removing it from the circuit. Other forms include ROM (read-only memory), PROM (programmable ROM), EPROM (erasable PROM) and EEPROM (electrically erasable ROM). Modern microcontrollers often use on-chip flash for program memory, with densities from a few kilobytes to several megabytes.

Programming program memory generally requires erasing prior content and writing new code. This can be done during manufacturing or in the field using programmers or in-system programming interfaces (for example SPI, JTAG, SWD). The endurance, write speed, and voltage requirements vary by technology; wear leveling and security features may be implemented to protect code integrity.

The design of program memory affects system boot processes, update mechanisms, and security. Because it stores the essential instructions for startup and operation, reliability and correct update procedures are critical.