内存管理

Logical address
Included in the machine language instructions to specify the address of an operand or of an instruction. This type of address embodies the well-known 80 × 86 segmented architecture that forces MS-DOS and Windows programmers to divide their programs into segments. Each logical address consists of a segment and an offset (or displacement) that denotes the distance from the start of the segment to the actual address.

Linear address (also known as virtual address)
A single 32-bit unsigned integer that can be used to address up to 4 GB - that is,up to 4,294,967,296 memory cells. Linear addresses are usually represented in hexadecimal notation; their values range from 0x00000000 to 0xffffffff.

Physical address
Used to address memory cells in memory chips. They correspond to the electrical. signals sent along the address pins of the microprocessor to the memory bus.Physical addresses are represented as 32-bit or 36-bit unsigned integers.
The Memory Management Unit (MMU) transforms a logical address into a linear address by means of a hardware circuit called a segmentation unit; subsequently, a second hardware circuit called a paging unit transforms the linear address into a physical address.
现代操作系统普遍采用虚拟内存管理机制，这需要MMU的支持。MMU通常是CPU的一部分，如果处理器没有MMU，或者有MMU但没有启用，CPU执行单元发出的内存地址将直接传到芯片引脚上，被内存芯片（物理内存）接收，这称为物理地址（Physical Address），如果处理器启用了MMU，CPU执行单元发出的内存地址将被MMU截获，从CPU到MMU的地址称为虚拟地址（Virtual Address），而MMU将这个地址翻译成另一个地址发到CPU芯片的外部地址引脚上，也就是将虚拟地址映射成物理地址