What const Really Is

At the C language level, const is only a type qualifier.
It tells the compiler:
That’s it.
The compiler enforces this rule at compile time, before any code runs.

Key point:

• const does not say where the data is stored
• const does not say the data is physically immutable

It is a promise enforced by the compiler, not by hardware

During compilation, const symbols are typically marked as:

• Read-only
• Non-writable

In the object file:

• The symbol metadata reflects immutability
• The compiler assumes the value never changes

But — and this matters —

• The compiler does not decide whether this lives in Flash or RAM.

That decision belongs to the linker.

The linker uses:

• Section attributes
• Linker script rules
• Target memory map

Common sections:

• .rodata → read-only data
• .data → initialized RAM data
• .bss → zero-initialized RAM

On many MCUs:
So by convention, const data often ends up in Flash.
But that is policy, not law.
Change the linker script, and this changes instantly

This is the most dangerous myth in embedded C.

Reality:

• const means read-only from C's perspective
• Flash placement is a linker decision
• Hardware may still modify the memory

Example:
const uint32_t calibration_value;
This could be:

• In Flash
• In RAM
• In external memory
• In shared memory updated by DMA

const does not imply physical immutability.