The Linear vs. the Physical Memory Address
As discussed in earlier chapters, when addressing memory the post-286 processor forms the 32-bit memory address by adding the 32-bit offset to the segment start address. The resultant 32-bit address is referred to as the linear address. If the OS has not enabled the processor's paging capability (CR0[PG] = 0), the linear address is the address that is used to address memory. In other words, the linear address and physical address are the same.
On the other hand, if the processor's paging capability is enabled (CR0[PG] = 1), the Paging Unit can convert, or map, the linear address to any physical memory address in the 4GB memory space. This is accomplished by using the 32-bit linear address ...