A personal computer system capable of preventing unauthorized user's access by way of a chip-in card including a card read and write unit for detecting the insertion or ejection of the chip-in card; a card read and write controller for generating an interrupt in response to the insertion or ejection of the chip-in card; at least one input means for allowing the user to input commands and information to gain access to the computer; and a host controller responsive to the interrupt from the card read and write controller, for preventing the input of commands and/or information from the input means, when the chip-in card is ejected, but allowing input of commands and information from the input means, when the chip-in card is inserted in position of the card read and write unit. Accordingly, the personal computer system can be controlled so that access to the computer or designated program cannot be realized without a personal identification card, while other unrestricted programs can be executed during the control of the computer system in order to increase its operation efficiency.