Introduction to security

I/O management

The I/O management subsystem controls all the input and output of the computer system. For the enforcement of security, the most important things that the I/O management subsystem does are

managing the transfer of data.
enforcing access controls (the DAC mechanisms) on data while it is being transferred. See ``Discretionary access control (DAC)'' for more information on DAC.

During the transfer of blocks or streams of data, and during character I/O operation, each I/O transaction is completely separate from all others. It follows a well-known and well-defined path; therefore, the integrity of all data is maintained during data transactions. Moreover, DAC permissions are enforced, securing the data from unauthorized access.