Q. What is IO Affinity?
A : There are two type of affinity, IO and CPU affinity, they are together called processor affinity.SQL is highly resource intensive, it is sometimes necessary to allocate CPU resource to sql.
If we have 4 CPUs we might need 2 CPUs to allocate to sql just for I/O operation and that is called IO affinity so it would be dedicated to input and output operation. By this way CPUs affinity and IO affinity can be set for all processor available and enhance the usage of CPUs.
It can be set through server-> processor
By default it is set to automatically set processor and IO affinity mask for all processor in this way sql engine can decide how much cpu will be used for different operation (SQL processor and IO modules.)