To provide the computer system which can securely protect data by allowing direct access from computers to one fixed magnetic disk and limiting access to data, computer by computer.

The computer system is constituted by connecting computer terminal devices 21 and 22 through a local area network 1. Data storage devices 11 and 13 provided to the computer terminal devices 21 and 22 are accessed directly not through the local area network 1. In addition to the said constitution, the data storage devices 11 and 14 are provided with a protect information area 12 which shows the computer terminal devices 21 and 22 are allowed to gain access, and the terminal devices 21 and 22 are allowed to access only data areas 13 of the data storage devices 11 and 14 specified by the protection information area 12.