historical log of data records

I need to keep a copy of old data as the rows are changed. 

For a general RDBMS I could think of keeping all the data in the same table with a flag to indicate older copies of updated /  deleted rows or keep a parallel table and copy these rows into the parallel data under program / trigger control. Each has its pros and cons. 

In Postgres would i have to follow the same methods or are there any features / packages available ?