How 32-bit system can address more than 4GB of RAM

The answer is Physical Address Extension (PAE)

Read more on the Section 3.8 of intel-sys.pdf.

Basically the page tables are now 64 bits addresses and there is 3 levels of hierarchy. Initial extension supported 36-bit extension, so the processor can address upto 64GiB of memory. Note that the addressing for the user is still 32-bit, so the user cannot use more than 4GiB of virtual address space.