Operating system note two: virtual address and Physical address/virtual memory

Wiki:

In computer science, the Physical address ( English:Physical Address), also known as the Real addresses , binary addresses (binary address), It is present in electronic form on the address bus, allowing the data bus to access the memory address of a particular storage unit in main memory.

In a computer with virtual memory, the term Physical address is used to differentiate between virtual addresses . In particular, in computers that use the Memory Management Unit (MMU) to convert memory addresses, the virtual and physical addresses refer to the addresses before and after the MMU conversion, respectively .

Baidu Encyclopedia:

Virtual Address (virtual address): After the CPU starts the protected mode , the program runs in the virtual addressing space. Note that not all "programs" are running in virtual addresses. The CPU is running in real mode at boot time, bootloader and the kernel does not use the virtual address before initializing the page table, but instead uses the physical address directly.

For 4G of memory space, each process has its own 4G address space, from 0X00000000-0XFFFFFFFF. Implemented by each process's own set of page catalogs and page tables. Because each process has its own page directory and page table, the physical memory mapped for each process's address space is not the same. The values for the same virtual address of two processes (if all have physical memory mappings) are generally different because they tend to correspond to different physical pages.

virtual Memory is a technology of computer system memory management. It allows the application to assume that it has contiguous available memory (a contiguous, complete address space), and in fact, it is usually separated into multiple physical memory fragments, and some are temporarily stored on external disk storage and exchanged for data when needed. Systems that use this technology make it easier to write large programs than systems that do not use virtual memory technology, and are more efficient at using real physical memory, such as RAM.

Operating system note two: virtual address and Physical address/virtual memory