A computer system, which has a host, a surface sensitive input device and an optical reader. The surface sensitive input device can be a display connected to the host for displaying output data of the host on its screen. The surface sensitive input device is divided into plural areas, each area having one or more indexes to represent a respective area code. The indexes are printed on the surface sensitive input device using a readable material to the optical reader. The optical reader is connected to the host and adapted to read the indexes on the surface sensitive input device for sending the indexes read to the host to further process.