File searching using variable length keys

Many computer applications require the storage of large amounts of information within the computer's memory where it will be readily available for reference and updating. Quite commonly, more storage space is required than is available in the computer's high-speed working memory. It is, therefore, a common practice to equip computers with magnetic tapes, disks, or drums, or a combination of these to provide additional storage. This additional storage is always slower in operation than the computer's working memory and therefore care must be taken when using it to avoid excessive operating time.