E820 Address Map描述(用C与Assembly混编)
OS必须知道系统物理内存的数量，才能够有效的使用和管理这些物理内存。所以在booting阶段，我们必须通过某种手段来检测和获取物理内存的总量。因此我们利用BIOS中断获取内存容量，常用的是INT 15h, AX=E820h - Query System Address Map的中断方法
,E820 Address Map describe (using C and Assembly mixed) OS system must know the number of physical memory in order to effectively use and manage the physical memory. So booting stage, we must by some means to detect and obtain the total amount of physical memory. Therefore, we use BIOS interrupt access to the amount of memory, commonly used is the INT 15h, AX = E820h- Query System Address Map interruption method