Data reader is usefull when we just want to acccess datas 
from the database not when we want to perform DML 
operations. and  It is usefull when we want to perform 
forward only reading of datas.It wont requires any 
large volume of resources in the Front end.

Datareader is read only or forward only.So it is very fast 
to fetch the data from database.

1)it is used for forward record only.

2)we cannot update or save

3)speed is fast than dataset

4)not persist any record

5)it is usefual in case of display data according to 
critiera on form using control like textbox,label etc.

who to use

in vb.net
dim sqlcmd as new sqlcmd("select ename from tblemp where 
empid=5;
dim dr as new dataReader
dr=sqlcmd.executeReader()
if dr.hasRows then
txtbox1.text(dr("ename"))
end if

this display ename in textbox.

its connection oriented architecture.

Datareader is used to fetch the data frm data source