file size saved on local system is nt same as the server

i have file 
Response.Clear()
Response.ContentType =
"application/octet-stream"
Response.AddHeader(Response.WriteFile(M_FILENAMe, "Content-Disposition", _"attachment; filename=""" & M_FILENAMe & """")True)Response.Flush()
Response.End()
the file is being saved on the  server  & needs to be same on the local system too so used the above code but the actual size is nt being saved on the local sys ...