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A stub file is a computer file which appears to be on the end-user's hard drive, but is actually hosted in part on another storage location. The most common secondary location for a stub file is network storage, in which the information is hosted online or on a network server physically connected to the system network. The main advantage to using stub files is that they make additional space available on the end-user's hard drive, allowing more files and programs to be saved on the system. One primary disadvantage is that accessing the stub file requires continual and uninterrupted access to the network computer containing the file.
Stub files take their names from the fact that they only contain "stubs" of their attendant files' actual data. A stub file works as a type of placeholder, reminding the computer — and the computer user — that the file is available for access. Once the end-user accesses a stub file, the computer takes the location information contained within it and routes it to the network device driver. The network card on the computer accesses the network storage location where the full contents of the stub file are stored, returning the information to the end-user's computer and displaying it onscreen like any other active file. From this point on, the end-user can view and modify the file as though it were actually and fully contained on the physical computer's hard drive.
Stub files are generally used as cost-saving devices. They allow organizations with significant amounts of data the capacity to move bulk portions of their data to lower-cost storage solutions, such as magnetic tape storage or lower-speed hard drives. This allows organizations to save their more expensive, faster hard drives for vital files and programs, while moving their archive or record files to the lower-cost storage medium.
Accessing stub files is generally slower than accessing non-stub files, as computers must utilize network resources to retrieve them, as opposed to collecting the data directly from host computers' hard drives. In addition to this, the ability to access stub files depends on constant operation of both the network and the storage medium hosting the full contents of the file; if either goes down, any stub files become inaccessible until the problem is resolved.