42_KFS/documentation/memory/mmu.md

Memory Management Unit (MMU)

The MMU is a chip which translate virtual memory to physical memory. When you try to access to an address (/!\ only when you try to access) the MMU will get the physical address from the pd.

How translate an address ?

The address will be divid in 3 parts:

• Page Directory index (10bit (cause 1024))
• Page Table index (10bit (cause 1024 too))
• offset (12bit cause page size = 4096)

Example

address: 0b000100000011101011111011101101

Base	PD index	PT index	offset
Binary	00010000	0011101011	111011101101
Decimal	16	235	3821

So to translate this address the MMU will get the 20 first bit of the value store at the 235th PTE of the 16th PDE and will replace the 20 first bit of the virtually address.