Computer system with separable input device

A computer system receives data from a separate input device, e.g. a personal digital assistant (PDA). The computer system is a desktop, laptop or notebook. The input device includes a memory, processor and touch screen. The input device can operate separately or when inserted into a recess in the casing of the computer system. The computer system includes two security features. A first security feature allows the input device to be used to enter data directly into the memory of the computer system. The second security feature permits synchronization of data between the computer system and the input device. The casing of the input device is configured to be compatible with the recess of the computer system casing.