Behavior of SqlBulkCopy with IDataReader in 3.5

How does SqlBulkCopy loads data into destination table in 3.5 when we call WriteToServer with IDataReader ? Does it stream directly to DB or does it load the stream in memory first completely and then sends to Sql ?

IN 4.5 I know there is EnableStreaming Property to control this. (ref: http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlbulkcopy.enablestreaming(v=vs.110).aspx)

But I want to be sure of what it does in 3.5.

Thanks for your help

Jyotsna