18_Memory Management Unit (MMU)

# Memory Management Unit (MMU)

The Memory Management Unit (MMU) is a computer hardware component responsible for handling accesses to memory requested by the CPU. It translates virtual addresses to physical addresses, an essential process in a virtual memory system.

## Memory Translation

Virtual memory is an abstraction of the main memory. It allows processes to believe they have contiguous addresses, while in reality, they might be scattered across the physical memory or even on disk storage. The MMU performs the translation using a Translation Lookaside Buffer (TLB).

```c
// C-like pseudocode
virtual_address = process_address
physical_address = MMU.Translate(virtual_address)
```

## Page Tables

The MMU uses a data structure called a page table to perform the translation. The page table maps virtual pages to physical frames. Each process has its own page table, and these are dynamically updated as processes are swapped in and out of memory.

```c
// C-like pseudocode
struct PageTableEntry {
    unsigned int FrameNumber;
    bool Valid;
    // Other attributes...
}

struct PageTable {
    PageTableEntry entries[MAX_ENTRIES];
}
```

## Memory Protection

The MMU also provides memory protection by assigning access rights for each page, such as read-only, read-write, or execute. When a process tries to access a page it does not have rights to, a fault is raised.

```c
// C-like pseudocode
if (!pageTableEntry.HasRights(requestedRights)) {
    raiseFault();
}
```

## Demand Paging and Swapping

The MMU supports demand paging, where pages are only loaded into memory when they are needed, and swapping, where pages are moved between memory and disk storage as needed.

```c
// C-like pseudocode
if (!pageTableEntry.Valid) {
    pageFaultHandler();
}
```

In summary, the MMU is a key component in modern computer systems, providing memory abstraction, protection, and efficient utilization.