Mapping from Page Table to Main Memory: Address Translation in Paging

Understand the address translation process in paging-based memory management systems. This tutorial details how the CPU uses page tables to map logical addresses (generated by a program) to physical addresses (locations in RAM), enabling efficient memory access in virtual memory systems.

Mapping from Page Table to Main Memory

Address Translation in Paging

In operating systems that use paging as a memory management technique, the CPU generates logical addresses, which need to be translated into physical addresses before the CPU can access the data in main memory. This translation process involves several steps that use a page table to map logical addresses (used by the program) to their corresponding physical addresses (locations in RAM).

Steps in Address Translation

1. Logical Address Generation

The CPU generates a logical address for each memory access. This address has two parts:

  • Page number: Identifies which page in the process's address space contains the data.
  • Offset: Specifies the location of the data within that page.

2. Scaling (Finding the Page Table Entry)

The CPU maintains a special register (a dedicated memory location within the CPU itself) that contains the starting address of the page table. To locate the correct entry in the page table for the requested page, the CPU adds the page table base address (from the register) to the page number from the logical address. This process is called scaling and provides the memory address of the relevant page table entry.

3. Physical Address Generation

The page table entry contains the frame number (the location in main memory) of the requested page. The CPU then combines this frame number with the offset (copied from the original logical address) to create a physical address. The physical address specifies the actual location of the data in RAM.

4. Accessing Main Memory

Finally, the CPU uses the physical address to access the requested data in main memory. The physical address is the actual memory location where the data is stored in RAM.