1. The Grand Illusion & Security
Every process thinks it owns the entire computer.
- Compilers assume memory is a clean, infinite, contiguous block. This is Virtual Memory.
- Security: By keeping processes in their own Virtual spaces, they are completely isolated. Process A cannot accidentally read Process B's data because their virtual addresses map to completely different physical locations.
2. Pages and Frames
We don't translate memory byte-by-byte; we move it in chunks.
- The OS chops Virtual Memory into blocks called Pages (e.g., 4KB).
- Physical RAM is chopped into matching blocks called Frames.
- This solves fragmentation! A process can have contiguous Virtual Pages that map to completely scattered, non-contiguous Physical Frames.
3. The Unchanging Offset
The MMU only translates the Page Number. The Offset stays identical.
- When the CPU asks for Virtual Address
0x2A4F, the Memory Management Unit (MMU) splits it.
2 is the Page Number (VPN). A4F is the Offset (the exact byte inside that 4KB page block).- The MMU looks up Page 2 in the Page Table. If it maps to Physical Frame 5, the true physical address becomes
0x5A4F. Notice how the A4F never changed!