Abstract: A personal computer subsystem, having a hardware module and protection software, is designed to protect files on a personal computer from inadvertent or intentional distortion, and can be used to protect personal computers from programs known as computer viruses. The hardware module is connected to the personal computer system busses and the software has a kernel which ensures the security of one access path to the hard disk controller and utilizes the above-mentioned module to block other access paths to the hard disk controller. The only permitted access path to the hard disk controller is a path which uses the computer's operating system, modular device driver and basic input/output system. All other access paths to the hard disk controller are interpreted by the personal computer subsystem as forbidden.