A cache is a group of files located in the cache directory. Each file contains a single thumbnail. The cache system has a maximum size limit. Once the limit is met, the oldest thumbnails in the cache will be purged for the newly visited thumbnails. The cache system runs automatically.
Catalogs are useful for directories that are used often or that have a large number of images.
Even though the cache will pull up images for frequently visited directories quickly, the storage of these images may keep other images from being cached. Also, you run the risk of purging items from the cache depending on the cache size. On the flip side, numerous catalogs can take up a large amount of disk space which can accumulate quickly if you catalog every image directory. We suggest utilizing a catalog for your frequently used image archives and let the cache handle any temporary or infrequently used image directories. This allows you to interrupt the thumbnail building process.