RAM Upgrade question

For further clarification, I am adding a 64Meg ram module to my existing 64Meg; the new one is a 133 mhz SDRAM DIMM 168 pin; my existing one is a 100Mhz SDRAM DIMM 168 pin..does the 133 have to go into the FIRST RAM slot or can it go into the currently empty 2nd slot…will the BIOS detect it in the 2nd slot?