Hi Vijay,
I have just completed the second chapter.
first of all we need to understand that SAS can only manage data made up of dataset. so when we reading a data from any source SAS will be storing this data resulted from reading to either Temp dataset or a permanent dataset.
so when we are reading data from raw data, SAS needs to create data dataset first (Input buffer, Program data vector and Data descriptor step used in DATA step) while in case of reading from Dataset this step not needed(Data is directly put in PDV).
Feb 17, 2013