Atmel datasheet

Hey it's really a small simple question, in the Atmel datasheets, when they give a register description they also put the register address, but i see two addresses, like : 0x32 (0x52), why are there two?
Thanks

See Note 4 at the bottom of the table:

  1. When using the I/O specific commands IN and OUT, the I/O addresses 0x00 - 0x3F must be used. When addressing I/O Registers as data space using LD and ST instructions, 0x20 must be added to these addresses. The ATmega48A/PA/88A/PA/168A/PA/328/P is a complex microcontroller with more peripheral units than can be supported within the 64 location reserved in Opcode for the IN and OUT instructions. For the Extended I/O space from 0x60 - 0xFF in SRAM, only the ST/STS/STD and LD/LDS/LDD instructions can be used.