When Director runs low on memory, it removes cast members from memory. You use the Property inspector to specify the priority with which a cast member is removed from memory. When a cast member is available in memory, it appears almost instantly. When it needs to be loaded from disk, the loading can cause a delay. Set your cast members so that frequently used cast members remain in memory as long as possible.
These settings are the same for all types of cast members.
3--Normal sets the selected cast members to be removed from memory after any priority 2 cast members are removed.
2--Next sets the selected cast members to be among the first removed from memory.
1--Last sets the selected cast members to be the last removed from memory.
0--Never sets the selected cast members to be retained in memory; these cast members are never unloaded.