The computer system includes a keyboard having a plurality of keys mounted in a supporting frame; a scanning device for sensing activation of keys; a processing device for generating commands and data units from status changes of the keys; a communication device for transmitting the generated commands and data units from the processing device; a rotatable dial having a center, a rotation axis passing through the center and an exposed operating surface and rotatably mounted in the supporting frame so as to be rotatable by contact of at least one finger of an operator with the operating surface at a plurality of radial positions spaced from the center of the dial; a rotational transducer device for generating an output signal according to an angular rotation speed of the dial in predetermined incremental angular units; a device for generating the sequences of repeated commands and data units from this output signal and a device for modifying the sequences of repeated commands and data units by activation of the keys when the dial is rotated by the operator.