FILE protocol

The FILE protocol can be used to retrieve data that are stored in files residing on your local file system as opposed to being obtained from external web servers. Because of its speed and because it does not rely on external servers, this is the preferred way of retrieving data when working with large datasets.
The FILE protocol currently only supports three data formats: BigBed (for Region Datasets), BigWig (for Numeric Datasets) and 2bit (for DNA Sequence Datasets). All of the data (i.e the whole genome) for a single track (and genome build) must be contained in a single file in one of these formats.