In
electronics terms, the recommended maximum
fanout of a device is the maximum number of
input loads a given
circuit element's
output can drive without deterioration in performance. The load seen by a given
circuit element's
output driver is a combination of the
input loads of the elements it drives and the
wireload of the
nets connecting these inputs to the
output driver.
Normally, a component's fanout is expressed in terms of a number of "standard load" units. The value of this "standard load" varies from one technology to the next, and is representative of the input load of a typical device from a given logic family. The larger a component's output driver, the higher its maximum fanout will be.
A high fanout net may need to be buffered in order that signals on the net are 'clean' enough to be used by the device inputs it drives.