What is the Device Control Block used for in Unity when configuring IO Scanner?

The Device Control Block is a flat address array of 8 contiguous words with each bit representing an entry in the I/O scanner for up to 128 logical device entries. With the bit set to 0, the IO Scanner operates for that entry. With the bit set to 1, that particular IO Scanner entry is disabled, and the Health bit (on supported controllers), is set to 1, representing an unhealthy state. This allows the developer to turn on or off individual IO Scanner entries based upon the state of each IO Scanner table entry bit