[Zope] ZODB vs SQL

In "Choosing to store data in SQL vs ZODB" located http://www.zope.org/Members/anthony/sql_vs_ZODB i read : "Will the data be frequently changing? If the data is going to be frequently changing, then it's not a good idea to put it in the ZODB. Every time the data changes, a new record will be appended to the Data.fs file - this could become a problem very quickly." Does that mean that the changes AND the old version of the object are kept in ZODB ? If it's true, is packing a good way to throw away the old versions of the object ? If Not, What are the good ways ? Well i hope that's my last question for today. Thanks Andre