The addresses programs use are virtual addresses. These are translated to real (physical) addresses by the OS and/or the CPU transparently to the program.
The following extract from here says it better.
Address translation
This means the virtual addresses generated by a program are different from the physical addresses that go onto the address bus; to the memory chips. The translation of virtual addresses to physical addresses is performed by special hardware inside the CPU called a memory management unit (MMU).
Address translation can be used for the kernel as well as the tasks. This lets you link the kernel to run at a specific address, but load the kernel anywhere in memory.
Besides address translation, the MMU usually provides memory protection. Ranges of memory can be made to cause a page fault or general protection fault by any combination of writing to the memory range,
accessing the memory range in any way (read, write, execute), access to the memory range by code running at user privilege (ring 3).
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