The first two settings are just switches to enable/disable disk caching and prefetching. Zero signifies off, one is on. Disk caching must be enabled for prefetching to take place, but disk caching can be on without prefetching. Next come the prefetching variables. The prefetch window (as defined previously) is the amount of time (in seconds) that is allowed to pass (once a new document is displayed), after which any followed links will not be considered for prefetching. That is to say, if a user accesses a link within the prefetch window, it will be added to the source documents prefetch list.
In making prefetch choices at run time, a destination URL will be prefetched if the ratio of the number of accesses of the destination to the total number of accesses of the source is greater than the prefetch probability (the next prefetching variable). So if the user visits the destination URL with a greater percent frequency than the prefetch probability, the URL will be prefetched (unless it is too big).
The last prefetch indicator is the maximum prefetch size. This is the maximum size (in bytes) that will be prefetched as one URL (image or text). The final user definable setting is the history type, which lets the user specify either the strict chronological history, or a slightly modified version of the original Mosaic global history. This setting can be switched between sessions without problems, although it is best to clear the global history once the change is made.