var file_, map : dword;
    buf: pointer;
begin
  file_ := CreateFile('c:\file1.txt', GENERIC_READ, FILE_SHARE_READ,
  nil, OPEN_EXISTING, 0, 0);
  if file_ <> INVALID_HANDLE_VALUE then
    try
      map := CreateFileMapping(file_, nil, PAGE_READWRITE, 0, 0, nil);
      if map <> 0 then
        try
          buf := MapViewOfFile(map, FILE_MAP_ALL_ACCESS, 0, 0, 0);
          if buf <> nil then
            try

              // now here you have your file1.txt in memory
              // beginning at pointer "buf"

            finally UnmapViewOfFile(buf) end;
        finally CloseHandle(map) end;
    finally CloseHandle(file_) end;
end;

{
This logic maps your complete file into memory. It's not COPIED into memory,
only MAPPED. In the moment where you access the single bytes of the file in
memory, Windows internally reads the file for you in the fastest possible way.
}