updating large table

Hi,

I have two tables tb1(KEY,IDS,col2,col3,col4) and tb2(key,col) each table has 90 milion records and i am updating tab2 data to tb1 using KEy coulmn

UPdate tb1

set IDS=col from tb2

where tb1.KEy=tb2.key

But it is taking to long to load the data in to main table can any one suggest me how to update quickly