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Hi,when the physical memory is over the 4gb such as 8gb memory,how the cpu recognize the physical address.

In 4gb mem,the max address is 0xffffffff,it is a limitation of 32 bit address,when the memory is over that value,how can i do?

The physical address space can be larger than the virtual address space. For example, 32-bit x86 has PAE and PSE-36, and ARM has LPAE.

Usually a PC with more than 3 gigabytes of ram isn't 32 bits, but rather 64 bits.