I am not sure what you are working with, or trying to achieve.
The IO is very fast. I can load 500,000 lines from multiple files before you can blink. In order to use IO in vb.net you should import it into the project you are working on. Here are some tips in that area.
at the top, and outside of the bounds of class form.
In order to use the system.io we need to get files.
Dim d As DirectoryInfo = New DirectoryInfo(Application.StartupPath & "\Files")<br />
Dim f As FileInfo<br />
For Each f In d.GetFiles<br />
Dim StreamReader As StreamReader = New StreamReader(F.FullName)<br />
Do Until StreamReader.EndOfStream<br />
Dim Str As String = StreamReader.ReadLine ‘ do something here<br />