Virtual Memory in Windows

I. Physical storage and address space

Physical storage and storage address space are two different concepts. However, because the two are closely related, and both use B, kb, MB, and GB to measure their capacity, it is easy to produce confusion. Understanding these two different concepts helps beginners further understand the primary memory and make good use of the primary memory.

Physical memory refers to the memory chip actually exists. For example, the main memory stick installed on the motherboard and the ROM chip with the system BIOS are loaded, the RAM chip is displayed on the display card, and the ROM chip is loaded with the display BIOS, and the RAM chip and ROM chip on a variety of adapter cards are physical memory.

The storage address space refers to the range of memory encoding (encoding address. The so-called encoding is to assign a number to each physical storage unit (one byte), which is usually called a "Addressing ". The purpose of allocating a number to a storage unit is to facilitate data reading and writing. This is the so-called "Addressing" (so someone also calls the address space an addressing space ).

The size of the address space is not necessarily the same as that of the physical storage. For example, the number of 17 rooms on a floor is 801 ~ 817. These 17 rooms are physical, and their address space uses three-digit encoding, with a range of 800 ~ 899 there are 100 addresses in total. It can be seen that the address space is larger than the actual number of rooms.

For a microcomputer of more than 386 grades, the address bus is 32-bit, so the address space can reach the power of 2, that is, 4 GB. But in fact, the physical memory we configured is usually only 1 MB, 2 MB, 4 MB, 8 Mb, 16 MB, 32 MB, etc., far smaller than the range allowed by the address space.

2. Memory ing, memory re ing, memory ing, address ing, address conversion, and other computer terms

Computer technology originated from the west, while the most common language in the west and even the world today is English. Therefore, many professional terms are also English words, chinese people want to keep up with the times to learn computers and use computers. They need to learn from Westerners, learn English, learn English technical materials, and translate English technical materials, however, after learning and translating, many professional English terms are translated into different Chinese meanings and appear in different materials and teaching materials (such as memory
Map, translated into memory ing, memory ing, address ing, etc.), causing everyone to be at a loss when reading these materials, teaching materials, what does it mean? So today I will focus on the above several confusing professional words based on my own opinions.

I. Memory ing, memory ing, and address ing

Before starting, you must first understand the meaning of ing. ing means a one-to-one correspondence, and re- ing means re-allocating this one-to-one correspondence.

Memory Map (which can be translated as memory ing and memory ing, also known as address map ))

One of the most important functional units of a computer is memory, which is a collection of many storage units. In order to make the CPU find a storage unit that stores certain information accurately, each unit must be assigned a unique number, which is the address code. In an embedded processor, multiple types of memory are integrated. We usually call a memory block of the same type. Generally, the processor designer will assign a continuous numerical value for each memory block. The number is equal to the number of storage units, and a 16-digit natural number set is used as the memory
Block address encoding. The correspondence between this natural number set and memory block is memory map (memory ing and memory ing), which is also called address map ). Here, we need to emphasize that memory map is a logical concept established after the computer system is reset (powered on. Memory Map is equivalent to a function in which the input value is address encoding and the output value is the data in the addressing unit. When the computer system powers down or resets, this function no longer exists, leaving only the physical basis for implementing this function-circuit connection. We can also think that memory map is a preparatory action when the computer system is powered on (reset, it is an automatic process of allocating the address encoding resources owned by the CPU to each physical memory block in the system.

Ii. Memory re ing, memory re ing, and address re ing

Memory remap (memory re ing, memory re ing, and address re ing)

Memory remap is closely related to the computer's abnormal (interrupted) processor. A complete computer system must be capable of handling exceptions (Interruptions. When an exception (Interruption) occurs, the CPU jumps to the preset memory unit under the hardware drive mechanism and retrieves the entry address of the corresponding exception handling program, enter the exception handling program based on the address. The memory unit that stores the abnormal program entry address is usually referred to as the "exception entry ". To simplify the chip design, the CPU designer generally places all abnormal entries in non-volatile memory and maps them to a fixed continuous address space when the system is powered on. The abnormal entry set located in this address space is the "abnormal vector table ".

Memory remap is a re-modification to the previously established memory map. In essence, the two are the same. They both allocate address encoding resources to memory blocks, but the two are generated at different times.

The remap technology is introduced to improve the system's real-time response to exceptions, that is, to solve the problem of communication between low-speed non-volatile memory and high-speed CPU.

The complete memory remap process usually starts with the bootload process. The specific execution process is: bootload copies the exception vectors in non-volatile memory to one end of the high-speed volatile memory block, and then runs the memory remap command, maps abnormal vectors in High-Speed volatile memory to the abnormal vector table address space. If the system generates an exception afterwards, the CPU reads the vector from the high-speed volatile memory mapped to the abnormal vector table address space. The typical Boot, memory map, and memory remap time sequence should be: Memory
Map -- boot -- Memory Remap.

Iii. address translation in the operating system (address ing and memory ing in some places)

1. physical address

Each unit in the memory has a unique ID, which becomes the memory address (physical address, absolute address). The set of memory addresses is called the memory space (or physical address space ).

2. Logical Address

The source program is compiled or compiled to form the target program. The addresses in the target program are called logical addresses (relative addresses), and each target program starts from 0 addresses.

3. Address Translation

The function of converting the logic addresses of commands or data in a user program into physical addresses in a bucket is called address conversion or relocation (some are called address ing and memory ing ). This process is generally completed by the memory management unit (MMU. There are two methods for address translation: static relocation and dynamic relocation.

Conclusion: different translations may confuse meanings or use the same professional vocabulary in different places, which makes it difficult for readers to understand the meaning of some professional vocabulary, therefore, I am writing this article here to express my comments. I hope you can give more guidance and unify the meaning of professional words so that everyone can learn more.

Reference: http://blog.csdn.net/songjinshi/article/details/6760708

Http://www.cnblogs.com/mydomain/archive/2011/01/07/1930404.html